Wednesday, December 31, 2014

SHARP LC26GA3E POWER SUPPLY AND SERVICE MODE


                      The adjustment values are set to the optimum conditions at the factory before shipping. If a value should become improper or an adjustment is required due to part replacement, make an adjustment according to the following procedure.

After replacement of any PWB unit and/or IC for repair, please note the following.
When replacing the PWB and IC, pay attention to the following precautions.
When replacing units below, order those where the software has been written.
DVI unit : DUNTKC595FE50
CPU unit : DUNTKC427FE20
LCD CONTROLLER unit : DUNTKC268FE86
Upgrading of each microprocessor software
Caution: Never "POWER OFF" the unit when software upgrade is ongoing.
Otherwise the system may be damaged beyond recovery.
Software version upgrade
This unit has main and monitor microcomputer softwares.
These can be rewritten via a general-purpose SD memory card.
The procedures to rewrite the main and monitor microcomputer softwares are described below.
Main software version upgrade
SD memory card of 16MB or higher capacity
 PC running on Windows 98/98SE/ME/2000/XP operating system
 SD memory card reader/writer with USB connectivity and PC card adapter
SD memory card formatting software

Entering and exiting the adjustment process mode (SERVICE)

1. Before entering the adjustment process mode, press the "TV RESET" button or execute the AV position RESET in the video adjustment menu.

2. Pull out the AC cord to turn off the TV.

3. While holding down the "VOL (–)" and "INPUT" keys at a time, press the POWER switch of the main unit to turn on the power.
The letter " K " appears on the screen.

4 Press the "VOL (–)" and CH (V) keys at the same time. When multiple lines of blue letters are displayed on the screen, the unit has entered the process adjustment mode. If the unit does not enter the process adjustment mode (if the same display as the normal start appears), try again.

5. To exit the adjustment process mode after the adjustment is done, unplug the AC cord from the outlet to make a forced shutdown. (When the power was turned off with the remote controller, once unplug the AC cord and plug it again. In this case, wait 10 seconds or so before plugging.)

Tuesday, December 30, 2014

HITACHI 36UX59B - 32UX59B - 36FX49B - 32FX49B - 36CX39B - 32CX39B - POWER SUPPLY AND SERVICE MODE

POWER SUPPLY CIRCUIT  AND SERVICE MODE 



SERVICE MODE 

 Adjustment Mode Chassis adjustment can be done by using the front control panel buttons with CTV set turned off. 

1. Press “POWER” and “INPUT” keys at the same time, and hold for more than 3 seconds. The CTV set turns on in adjustment mode with OSD

2.Changing Data and Adjustment Code When the CTV set is in adjustment mode, the cursor UP AND DOWN  and MENU keys of the customers remote control  will be the adjustment keys.

3. Use any Hitachi remote control when making an adjustment

4. UP and DOWN keys are used for changing adjustment code.

5. LEFT and RIGHT  keys are used for changing data

6. MENU key is used for changing “Cut Off Mode ”/” Normal mode.”

To  Escape from Adjustment Mode” Press “POWER” button of remote control  or front panel once at anytime. Then set returns to normal state.



Sunday, December 28, 2014

HITACHI - 43F300 - 53F300 -POWER SUPPLY AND SERVICE MODE

POWER SUPPLY CIRCUIT AND SERVICE MODE 



SERVICE MODE 

1.Press and hold INPUT key on control panel and then press POWER key on control panel to access i2c (Service mode) adjustment mode.

2.Use CURSOR UP and DOWN on remote to select data.

3. Use CURSOR LEFT and RIGHT to adjust data.

3. Press EXIT key to exit i2c (Service mode).


Thursday, December 25, 2014

PHILIPS BJ 3.0E CHASSIS- 37 INCH LCD POWER SUPPLY- ERRORS CODES

         PHILIPS  BJ 3.0E CHASSIS- 37 INCH

Error Codes

Introduction
 
                       The error code buffer contains all detected errors since the last time the buffer was erased. The buffer is written from left to right, new errors are logged at the left side, and all other errors shift one position to the right. When an error occurs, it is added to the list of errors, provided the list is not full. When an error occurs and the error buffer is full, then the new error is not added, and the error buffer stays intact (history is maintained), except when the error is a protection error. To prevent that an occasional error stays in the list forever, the error is removed from the list after more than 50 hrs. of operation. When multiple errors occur (errors occurred within a short time span), there is a high probability that there is some relation between them.

Basically there are three kinds of errors:

* Errors detected by the Stand-by Processor. These errors will always lead to protection and an automatic start of the blinking LED for the concerned error (see paragraph “The Blinking LED Procedure”). In these cases SDM can be used to start up (see chapter “Stepwise Start-up”). Note that it can take up to 90 seconds before the TV goes to protection and starts blinking the error (e.g. error 53)

* Errors detected by VIPER that lead to protection. In this case the TV will go to protection and the front LED should also blink the concerned error. Depending on the software version it is possible that this mechanism does not work. See also paragraph “Error Codes” -> “Error Buffer” -> “Extra Info”.

* Errors detected by VIPER that do not lead to protection. In this case the error will be logged into the error buffer and can be read out via ComPair, via blinking LED method, or in case you have picture, via SAM.
How to Read the Error Buffer
Use one of the following methods:

* On screen via the SAM (only if you have a picture). E.g.:
– 00 00 00 00 00: No errors detected
– 06 00 00 00 00: Error code 6 is the last and only detected error
– 09 06 00 00 00: Error code 6 was first detected and
error code 9 is the last detected error

* Via the blinking LED procedure (when you have no picture). See next paragraph.

* Via ComPair.

How to Clear the Error Buffer Use one of the following methods:

* By activation of the “RESET ERROR BUFFER” command in the SAM menu.
* With a normal RC, key in sequence “MUTE” followed by “062599” and “OK”.
* If the content of the error buffer has not changed for 50+ hours, it resets automatically.

Error Buffer

In case of non-intermittent faults, clear the error buffer before you begin the repair (before clearing the buffer, write down the content, as this history can give you significant information).

This to ensure that old error codes are no longer present. If possible, check the entire contents of the error buffer. In some situations, an error code is only the result of another error code and not the actual cause (e.g., a fault in the protection detection circuitry can also lead to a protection).

There are several mechanisms of error detection:
* Via error bits in the status registers of ICs.
*Via polling on I/O pins going to the stand-by processor.
* Via sensing of analogue values on the stand-by processor or the Viper.
* Via a “not acknowledge” of an I2C communication Take notice that some errors need more than 90 seconds before they start blinking. So in case of problems wait 2 minutes from start-up onwards, and then check if the front LED is blinking.

Rebooting. When a TV is constantly rebooting due to internal problems, most of the time no errors will be logged or blinked. This rebooting can be recognised via a compare interface and Hyperterminal (for Hyperterminal settings,). You will see that the loggings which are generated by the main software keep continuing. In this case (rebooting) diagnose has to be done via ComPair.

* Error 1 (I2C bus 1 blocked). When this error occurs, the TV will go to protection and the front LED will blink error 1. Now you can start up the TV via the SDM short-cut pins on the SSB. The TV will start up and ignore the error. Depending on the problem it is even possible that you have picture.

* Error 2 (I2C bus 2 blocked). Due to hardware restriction (I2C bus 2 is the fast I2C bus) it will be impossible to start up the VIPER when I2C bus 2 is blocked. When this error occurs, the TV will not start up (but probably you will seethe green LED). Starting up the TV via the SDM short-cut pins will not work. So it will not be possible to read out error 2 via internal software (allthough it will be logged). Use ComPair for further diagnose (e.g. read out the NVM content).

* Error 3 (I2C bus 3 blocked). There are only three devices on I2C bus 3: VIPER, Stand-by Processor, and NVM. The Stand-by Processor is the detection device of this error, so this error will only occur if the VIPER or the NVM is blocking the bus. This error will also blink when the NVM gives no acknowledge on the I2C bus. Note that if the 12 V supply is missing, the DC/DC supply on the SSB will not work. Therefore the VIPER will not get supplies and could block I2C bus 3. So, a missing 12 V can also lead to an error 3.

* Error 4 (I2C bus 4 blocked). When this error occurs, the TV will go to protection and the front LED will blink error 4. Now you can start up the TV via the SDM short-cut pins on the SSB. The TV will start up and ignore the error. Depending on the problem it is even possible that you have picture.

• Error 5 (VIPER does not boot). This error will point to a severe hardware problem around the VIPER (supplies not OK, VIPER completely dead, I2C link between VIPER and Stand-by Processor broken, etc...).

* Error 7 (8V6 error). In case of a TV with SDI display you will see error 7 blink in case of an audio protection. So except a problem with the 8V6 itself it is also possible that there is something wrong with the audio part. See also paragraph "Hardware Protections" for this.

* Error 14 (Audio protection). The detection is done on theaudio board itself. Several items are monitored: overvoltage, overcurrent, DC level on the speakers and the audio supply voltages. If one of these items fails, the audioprotection will switch off the main supply. All supplies will drop, the standby processor “thinks” there is a mains dip, and will reboot. At the beginning of the boot process, the audio-protection line is monitored: if this line is “active”, the set will go to protection and will blink error 14.

* Error 27 (PNX2015 HD subsystem part). Diagnosing this error will not be possibly via the normal errorcodes. In case this device can not communicate with the Viper via I²C, it will not be possible to initialise the tunnelbus. Hence the software will not be able to start up, and will re-boot constantly. Diagnosing these problems will only be possible via ComPair. In theory it is possible that the error is logged in the NVM (that’s why this error is still mentioned here).

* Error 29 (AVIP 1). Same remark as for error 27.

* Error 31 (AVIP 2). Same remark as for error 27.

* Error 44 (NVM). This error will probably never occur because it is masked by error 3 (I2C bus 3). The detection mechanism for error 3 checks on an I2C acknowledge of the NVM. If NVM gives no acknowledge, the stand-by software assumes that the bus is blocked, the TV goes to protection and error 3 will be blinking..

* Error 46 (Pacific 3). When this errors occurs the TV will go to stand-by. The reason for this is, when there is an occasional boot problem of the Pacific, it will look like the TV has started up in stand-by mode, and the customer can switch it on again. When there is an actual problem with or around the Pacific the TV will go to stand-by every time you try to start up. So this behaviour is an indication of a Pacific problem.

* Error 53. This error will indicate that the VIPER has started to function (by reading his boot script, if this would have failed, error 5 would blink) but initialization was never completed because of hardware peripheral problems (NAND flash, ...) or software initialization problems. Possible cause could be that there is no valid software loaded (try to upgrade to the latest main software version).
Note that it takes 90 seconds before the TV goes to protection in this case.

* Error 55 (SPIDER error). Same remark as for error 27.

* Error 63 (POWER OK). When this error occurs, it means that the POWER-OK line did not became “high”. This error is only applicable for TV’s with a SDI display, a FHP display or a Sharp full HD display. Depending on the software version it is possible that the detection mechanism of this error does not function and that the TV keeps rebooting.

* Error 64 (Display error). When this error occurs it means that there is a problem with the I2C communication towards the display. Allthough several display types communicate via I2C, this error will only work for TV’s with a FHP display.
The Blinking LED Procedure
Introduction

The blinking LED procedure can be split up into two situations:

* Blinking LED procedure in case of a protection detected by the stand-by processor. In this case the error is automatically blinked. This will be only one error, namely the one that is causing the protection. Therefore, you do not have to do anything special, just read out the blinks. A long blink indicates the decimal digit, a short blink indicates the units.

* Blinking LED procedure in the “on” state. Via this procedure, you can make the contents of the error buffer visible via the front LED. This is especially useful for fault finding, when there is no picture. When the blinking LED procedure is activated in the “on” state, the front LED will show (blink) the contents of the error-buffer.
Error-codes > 10 are shown as follows:

1. “n” long blinks (where “n” = 1 - 9) indicating decimal digit,
2. A pause of 1.5 s,
3. “n” short blinks (where “n”= 1 - 9),
4. A pause of approx. 3 s.
5. When all the error-codes are displayed, the sequence finishes with a LED blink of 3 s,
6. The sequence starts again. Example: Error 12 8 6 0 0.
After activation of the SDM, the front LED will show:
1. 1 long blink of 750 ms (which is an indication of the decimal digit) followed by a pause of 1.5 s,
2. 2 short blinks of 250 ms followed by a pause of 3 s,
3. 8 short blinks followed by a pause of 3 s,
4. 6 short blinks followed by a pause of 3 s,
5. 1 long blink of 3 s to finish the sequence,
6. The sequence starts again.



Tuesday, December 23, 2014

HAIER LTF42K1 AND LTF47K1 POWER SUPPLY CIRCUIT WITH POWER FACTOR CORRECTION

  HAIER LTF42K1 AND LTF47K1

SOME NOTES ABOUT POWER FACTOR CORRECTION (PFC)

                        Every year, millions and millions of notebook computers, LCD monitors and LCD televisions are produced. With such a fast growing number of these and other electronic devices using more and more power, actions must to be taken to ensure the functionality of the nationwide power grid. In 2001, the European Union put EN61000-3-2 into effect to set the harmonic regulation standard on any power grid supplied application with power consumption over 75 watts. This essentially requires power factor correction (PFC). Additionally, a standby power dissipation limit is set to conserve power when a load is OFF. “80 PLUS” is an initiative funded by electric utilities to integrate more energy efficient Power Supply Units (PSUs) - especially for desktop computers and servers. 80 PLUS certifies to more than 80% energy efficiency at 20%, 50% and 100% of rated load. To meet the 80 PLUS certification, PSUs require a PFC of 0.9 or greater at 100% load. This means PSUs that waste 20% or less electric energy (as heat at the specified load levels) will lead to reduced electricity consumption and lower bills. Rebates are sometimes given to manufacturers who use 80 PLUS certified PSUs. Implementing power factor correction (PFC) into switch mode power supplies will maximize:

1 .The power handling capability of the power supply

2.Current handling capacities of power distribution networks Input power factor (PF) is defined as:

PFC = REAL POWER (WATTS) / APPARENT POWER (VA )

PF is expressed as decimal number between zero and one (0 and 1). A non-corrected power supply with a typical PF equal to 0.65 will draw approximately 1.5 times greater input current than a PFC supply (PF = 0.99) for the same output loading. The non-corrected supply requires additional AC current to be generated which is not consumed by the load, creating I 2R losses in the power distribution network. There are two types of PFCs:

1. Active

2. Passive

Passive PFC

The simplest form of PFC is passive (Passive PFC). A passive PFC uses a filter at the AC input to correct poor power factor. The passive PFC circuitry uses only passive components > an inductor and some capacitors

Active PFC
 
Active PFC offers better THD and is significantly smaller and lighter than a passive PFC circuit. To reduce the size and cost of passive filter elements, an active PFC operates at a higher switching frequency than the 50Hz/60Hz line frequency.
Active PFC functions include:
1. Active wave shaping of the input current
2. Filtering of the high frequency switching
3. Feedback sensing of the source current for waveform control
4. Feedback control to regulate output voltage




17PW46 TFT LCD POWER SUPPLY CIRCUIT DIAGRAM

                          17PW46 TFT LCD 

                   
SAFETY GUIDANCE 
                These guidelines are to protect you from potentially deadly electrical shock hazards as well as the equipment from accidental damage. Note that the danger to you is not only in your body providing a conducting path, particularly through your heart. Any involuntary muscle contractions caused by a shock, while perhaps harmless in themselves, may cause collateral damage - there are many sharp edges inside this type of equipment as well as other electrically live parts you may contact accidentally.

The purpose of this set of guidelines is not to frighten you but rather to make you aware of the appropriate precautions. Repair of TVs, monitors, microwave ovens, and other consumer and industrial equipment can be both rewarding and economical. Just be sure that it is also safe!

Don't work alone - in the event of an emergency another person's presence may be essential.

1.Always keep one hand in your pocket when anywhere around a powered line-connected or high voltage system. Wear rubber bottom shoes or sneakers.

2.Don't wear any jewelry or other articles that could accidentally contact circuitry and conduct current, or get caught in moving parts.

3.Set up your work area away from possible grounds that you may accidentally contact.

4.Know your equipment: TVs and monitors may use parts of the metal chassis as ground return yet the chassis may be electrically live with respect to the earth ground of the AC line. Microwave ovens use the chassis as ground return for the high voltage. In addition, do not assume that the chassis is a suitable ground for your test equipment!

5.If circuit boards need to be removed from their mountings, put insulating material between the boards and anything they may short to. Hold them in place with string or electrical tape. Prop them up with insulation sticks - plastic or wood.

6. If you need to probe, solder, or otherwise touch circuits with power off, discharge (across) large power supply filter capacitors with a 2 W or greater resistor of 100 to 500 ohms/V approximate value (e.g., for a 200 V capacitor, use a 20K to 100K ohm resistor). Monitor while discharging and verify that there is no residual charge with a suitable voltmeter. In a TV or monitor, if you are removing the high voltage connection to the CRT (to replace the flyback transformer for example) first discharge the CRT contact (under the suction cup at the end of the fat HV wire). Use a 1M to 10M ohm 5 W or greater wattage (for its voltage hold off capability, not power dissipation) resistor on the end of an insulating stick or the probe of a high voltage meter. Discharge to the metal frame which is connected to the outside of the CRT.

7. For TVs and monitors in particular, there is the additional danger of CRT implosion - take care not to bang the CRT envelope with your tools. An implosion will scatter shards of glass at high velocity in every direction. There are several tons of force attempting to crush the typical CRT. While implosion is not really likely even with modest abuse, why take chances? However, the CRT neck is relatively thin and fragile and breaking it would be very embarrassing and costly. Always wear eye protection when working around the back side of a CRT.

8. Connect/disconnect any test leads with the equipment unpowered and unplugged. Use clip leads or solder temporary wires to reach cramped locations or difficult to access locations.
9. If you must probe live, put electrical tape over all but the last 1/16" of the test probes to avoid the possibility of an accidental short which could cause damage to various components. Clip the reference end of the meter or scope to the appropriate ground return so that you need to only probe with one hand.

10. Performe as many tests as possible with power off and the equipment unplugged. For example, the semiconductors in the power supply section of a TV or monitor can be tested for short circuits with an ohmmeter.

11. Use an isolation transformer if there is any chance of contacting line connected circuits. A Variac(tm) is not an isolation transformer! The use of a GFCI (Ground Fault Circuit Interrupter) protected outlet is a good idea but will not protect you from shock from many points in a line connected TV or monitor, or the high voltage side of a microwave oven, for example. (Note however, that, a GFCI may nuisanse trip at power-on or at other random times due to leakage paths (like your scope probe ground) or the highly capacitive or inductive input characteristics of line powered equipment.) A fuse or circuit breaker is too slow and insensitive to provide any protection for you or in many cases, your equipment. However, these devices may save your scope probe ground wire should you accidentally connect it to a live chassis.

12. Don't attempt repair work when you are tired. Not only will you be more careless, but your primary diagnostic tool - deductive reasoning - will not be operating at full capacity.

13. Finally, never assume anything without checking it out for yourself! Don't take shortcuts!

Monday, December 22, 2014

QSC RMX 2450 CIRCUIT DIAGRAM AND BIAS SETTING

  QSC RMX 2450 


RMX 2450 calibration procedures
Setting bias
Always set the bias
> after replacing any output or driver transistor.
> after replacing any diode or resistor in the driver/output circuitry.
>  if the amplifier seems to run too hot at idle.
> if the amplifier exhibits crossover distortion.

The bias network sets the quiescent base current in the NPN and PNP driver transistors, which in turn sets the quiescent current in the output transistors. The driver transistors should both be slightly “on” at idle so that the transitions of the signal voltage between positive and negative are smooth and free of gaps or glitches. Too much bias current will cause the amplifier to run hotter than it should, especially at idle, while too little will cause noticeable crossover distortion, especially at low signal levels. The amplifier circuitry must be cool, or at least within a couple degrees of ambient air temperature, and the top cover must be removed. If the driver and output transistors are significantly warmer than the ambient air, leave the amplifier off and let it cool
before proceeding. Before turning the amplifier on to set bias on one or both channels, familiarize yourself with the locations of the trimpots (R131 and
R231) and the voltage measuring points so you can work quickly but thoroughly. If the amplifier warms up before you finish setting the bias, you will need to shut the amplifier off and let it cool down before you resume.
Tools and resources you will need:
1. Small flat screwdriver (non-conductive) for adjusting trimpots
2. DC voltmeter
3. AC power
Procedure
1. Turn the amplifier’s gain controls all the way down. No test signal is needed.
2. Plug the amplifier into an appropriate AC source. Turn the amplifier on.
3. Channel 1: While measuring the DC voltage across resistor R146, adjust trimpot R131 to obtain the voltage listed in Table 1.
4. Channel 2: While measuring the DC voltage across resistor R246, adjust trimpot R231 to obtain the voltage listed in Table 1.
After setting the bias, calibrate the positive and negative current limiting; instructions for the procedure follow below

Setting positive and negative current limits
Tools and resources you will need
1.Oscilloscope
2. 2-ohm resistive load (rated for at least 1200 watts)
3. Shorting connector for amplifier output
4. Variable AC transformer (e.g., Variac, Powerstat, etc.) rated for 25A (120V) or 12A (230V). Make sure the AC supply is appropriate for the amplifier.
5. 1 kHz audio sine wave generator
6.  Digital multimeter
7. Clamp-on digital current meter (e.g., Fluke 30 Clamp Meter)
8. Small flat screwdriver (nonconductive) for adjusting trimpots

Procedure
1. Set the audio sine generator to 1 kHz at 1 volt RMS and connect it to Channel 1's input. Connect a 2-ohm load and the oscilloscope probe across Channel 1's output.
2. Turn up Channel 1's gain control partway. On the oscilloscope you should see the amplitude of the sine wave increase accordingly.
3. Turn the gain control back down and apply a short circuit across the output terminals of Channel 1. Clamp a current probe either onto one of the brown wires running to the AC switch or onto
4. Turn the gain control all the way up. Adjust trimpots R139 and R140 equally until the current measured falls within the range shown in Table below.
5. Turn the gain control all the way down and remove the short circuit so the channel drives the 2-ohm load. Turn the gain control back up until the output clips. The voltage at which the signal starts to clip should fall within the range shown in Table below. If the clipping is asymmetrical, that is, the signal clips on either the positive or negative side first, adjust R139 to make it symmetrical.
6. Turn the gain control down. If the amp has begun to warm up shut it off and let it cool a few minutes before proceeding with Channel 2.
7. Repeat steps 1 through 5 for Channel 2. Use trimpots R239 and R240 to adjust the current limiting in steps 11 and 12.
8. Turn both channels’ gain controls all the way down. Clamp the ammeter onto one of the amp’s AC wires and check the amp’s idle current. If the amplifier is still at about room temperature, the idle current should match the value shown in Table below.

Removing the channel modules
1. Disconnect the amplifier from AC power and allow at least 10 minutes for internal voltages to bleed down.
2. Using a Philips screwdriver, remove the screws that fasten the top cover to the chassis. Also remove the top cover’s four recessed screws that fasten it to the heat sinks. As you remove screws, set them aside, but also make note of where each type is used so you can properly re-assemble the amplifier.
3. Lift the top cover up at the rear and carefully pull it toward the back, removing the five hooks on the front edge from their slots in the chassis.
4. Pull the gain control knobs straight off from the potentiometer shafts.
5. Tip the amplifier up on its side and remove the four screws that fasten the heat sinks to the chassis.
6. Set the amplifier back down and remove the screws that mount the channel modules to the chassis standoffs. There are six screws in the left module and five in the right one.
7. Remove the four screws that fasten the fan, fan shroud, and fan guard to the chassis. Lift the fan shroud out from the chassis; this will give you room to properly remove the modules from the chassis.
8. Disconnect the wire and cable connections to the channel modules. All of the connections are either detachable headers or ¼-inch quick-connect tabs that are disconnected by pulling them straight up. No unsoldering is necessary.
9. Slide the channel modules toward the back so the potentiometer shafts and front panel LEDs are clear of their holes in the front panel. Lift the channel modules out from the chassis.
10. Re-assembly is the opposite of disassembly.
Removing the AC board
The AC board provides AC voltage selection, rectification of the transformer secondary current, and a regulated DC supply for the cooling fan. It seldom needs to be replaced unless it is physically damaged itself. Most failures involving the AC board can be repaired through replacement of individual components.
WARNING: Regulatory agencies require that any operating voltage conversions from 120 volts to any other voltage be done onlyby QSC’s factory service. Any other operating voltage conversions may be done only by a QSC-authorized service center or international distributor.
1. Disconnect the amplifier from AC power and allow at least 10 minutes for internal voltages to bleed down.
2. Remove the four screws that fasten the fan, fan shroud, and fan guard to the chassis. Lift the fan shroud out from th chassis.
3. Disconnect the wires that connect to the channel modules. All of the large single wires attach to the channel modules with ¼-inch quick-connect tabs that are detached by pulling them straight up. The remaining three black wires disconnect at the left channel module with a detachable header. If you are planning to replace the AC board with another, carefully cut each of the transformer wires connecting to the board just above its solder tab. You must leave enough slack to allow connection to the new AC board. Remove the old heat shrink tubing from the wires and strip the wire ends about 0.25 inch or 6.3 mm.
4. Remove the five screws that attach the AC board to the chassis standoffs. Lift the board out from the chassis.
5. Re-assembly is the opposite of disassembly. If you’re using a new AC board, slide new pieces of heat shrink tubing over the transformer wires before you solder them to the appropriate tabs on the board; after soldering, cover the joints with the tubing and use a heat gun or other heat source to shrink them tightly.


Sunday, December 21, 2014

QSC RMX 850 CALIBARTAION AND BIAS ADJSUTSMNET

QSC RMX 850

MECHANICAL DIS ASSEMBLY AND REASSEMBLY 

Removing the channel modules
 
1. Disconnect the amplifier from AC power and allow at least 10 minutes for internal voltages to bleed down.
2. Using a Philips screwdriver, remove the screws that fasten the top cover to the chassis. Also remove the top cover’s four recessed screws that fasten it to the heat sinks. As you remove screws, set them aside, but also make note of where each type is used so you can properly re-assemble the amplifier.
3. Lift the top cover up at the rear and carefully pull it toward the back, removing the five hooks on the front edge from their slots in the chassis.
4. Pull the gain control knobs straight off from the potentiometer shafts.
5. Tip the amplifier up on its side and remove the four screws that fasten the heat sinks to the chassis.
6. Set the amplifier back down and remove the screws that mount the channel modules to the chassis standoffs. There are six screws in the left module and five in the right one.
7. Remove the four screws that fasten the fan, fan shroud, and fan guard to the chassis. Lift the fan shroud out from the chassis; this will give you room to properly remove the modules from the chassis.
8. Disconnect the wire and cable connections to the channel modules. All of the connections are either detachable headers or ¼-inch quick-connect tabs that are disconnected by pulling them straight up. No unsoldering is necessary.
9. Slide the channel modules toward the back so the potentiometer shafts and front panel LEDs are clear of their holes in the front panel. Lift the channel modules out from the chassis.
10. Re-assembly is the opposite of disassembly.
Removing the AC board

The AC board provides AC voltage selection, rectification of the transformer secondary 
current, and a regulated DC supply for the cooling fan. It seldom needs to be replaced unless it is physically damaged itself. Most failures involving the AC board can be repaired through replacement of individual components.
WARNING: Regulatory agencies require that any operating voltage conversions from 120 volts to any other voltage be done onlyby QSC’s factory service. Any other operating voltage conversions may be done only by a QSC-authorized service center or international distributor.
1. Disconnect the amplifier from AC power and allow at least 10 minutes for internal voltages to bleed down.
2. Remove the four screws that fasten the fan, fan shroud, and fan guard to the chassis. Lift the fan shroud out from th chassis.
3. Disconnect the wires that connect to the channel modules. All of the large single wires attach to the channel modules with ¼-inch quick-connect tabs that are detached by pulling them straight up. The remaining three black wires disconnect at the left channel module with a detachable header. If you are planning to replace the AC board with another, carefully cut each of the transformer wires connecting to the board just above its solder tab. You must leave enough slack to allow connection to the new AC board. Remove the old heat shrink tubing from the wires and strip the wire ends about 0.25 inch or 6.3 mm.
4. Remove the five screws that attach the AC board to the chassis standoffs. Lift the board out from the chassis.
5. Re-assembly is the opposite of disassembly. If you’re using a new AC board, slide new pieces of heat shrink tubing over the transformer wires before you solder them to the appropriate tabs on the board; after soldering, cover the joints with the tubing and use a heat gun or other heat source to shrink them tightly.


SETTING BIAS 

Always set the bias
> after replacing any output or driver transistor.
> after replacing any diode or resistor in the driver/output circuitry.
>  if the amplifier seems to run too hot at idle.
> if the amplifier exhibits crossover distortion.

The bias network sets the quiescent base current in the NPN and PNP driver transistors, which in turn sets the quiescent current in the output transistors. The driver transistors should both be slightly “on” at idle so that the transitions of the signal voltage between positive and negative are smooth and free of gaps or glitches. Too much bias current will cause the amplifier to run hotter than it should, especially at idle, while too little will cause noticeable crossover distortion, especially at low signal levels. 

            The amplifier circuitry must be cool, or at least within a couple degrees of ambient air temperature, and the top cover must be removed. If the driver and output transistors are significantly warmer than the ambient air, leave the amplifier off and let it cool before proceeding. Before turning the amplifier on to set bias on one or both channels, familiarize yourself with the locations of the trimpots (R131 and R231) and the voltage measuring points so you can work quickly but thoroughly. If the amplifier warms up before you finish setting the bias, you will need to shut the amplifier off and let it cool down before you resume.

Tools and resources you will need:
 
1. Small flat screwdriver (non-conductive) for adjusting trimpots
2. DC voltmeter
3. AC power

Procedure
 
1. Turn the amplifier’s gain controls all the way down. No test signal is needed.
2. Plug the amplifier into an appropriate AC source. Turn the amplifier on.
3. Channel 1: While measuring the DC voltage across resistor R146, adjust trimpot R131 to obtain the voltage listed in Table 1.
4. Channel 2: While measuring the DC voltage across resistor R246, adjust trimpot R231 to obtain the voltage listed in Table 1.
After setting the bias, calibrate the positive and negative current limiting; instructions for the procedure follow below

Setting positive and negative current limits

Tools and resources you will need
 
1.Oscilloscope
2. 2-ohm resistive load (rated for at least 1200 watts)
3. Shorting connector for amplifier output
4. Variable AC transformer (e.g., Variac, Powerstat, etc.) rated for 25A (120V) or 12A (230V). Make sure the AC supply is appropriate for the amplifier.
5. 1 kHz audio sine wave generator
6.  Digital multimeter
7. Clamp-on digital current meter (e.g., Fluke 30 Clamp Meter)
8. Small flat screwdriver (nonconductive) for adjusting trimpots

Procedure
1. Set the audio sine generator to 1 kHz at 1 volt RMS and connect it to Channel 1's input. Connect a 2-ohm load and the oscilloscope probe across Channel 1's output.
2. Turn up Channel 1's gain control partway. On the oscilloscope you should see the amplitude of the sine wave increase accordingly.
3. Turn the gain control back down and apply a short circuit across the output terminals of Channel 1. Clamp a current probe either onto one of the brown wires running to the AC switch or onto
4. Turn the gain control all the way up. Adjust trimpots R139 and R140 equally until the current measured falls within the range shown in Table below.
5. Turn the gain control all the way down and remove the short circuit so the channel drives the 2-ohm load. Turn the gain control back up until the output clips. The voltage at which the signal starts to clip should fall within the range shown in Table below. If the clipping is asymmetrical, that is, the signal clips on either the positive or negative side first, adjust R139 to make it symmetrical.
6. Turn the gain control down. If the amp has begun to warm up shut it off and let it cool a few minutes before proceeding with Channel 2.

7. Repeat steps 1 through 5 for Channel 2. Use trimpots R239 and R240 to adjust the current limiting in steps 11 and 12.
8. Turn both channels’ gain controls all the way down. Clamp the ammeter onto one of the amp’s AC wires and check the amp’s idle current. If the amplifier is still at about room temperature, the idle current should match the value shown in Table below.

BIAS TABLE FOR RMX 850
CLICK ON THE IMAGE TO ZOOM IN

QSC RMX 850 CIRCUIT DIAGRAM- BIAS ADJUSTMENTS AND CALIBRATION

          QSC RMX 850

RMX calibration procedures

Setting bias

Always set the bias
> after replacing any output or driver transistor.
> after replacing any diode or resistor in the driver/output circuitry.
>  if the amplifier seems to run too hot at idle.
> if the amplifier exhibits crossover distortion.

The bias network sets the quiescent base current in the NPN and PNP driver transistors, which in turn sets the quiescent current in the output transistors. The driver transistors should both be slightly “on” at idle so that the transitions of the signal voltage between positive and negative are smooth and free of gaps or glitches. Too much bias current will cause the amplifier to run hotter than it should, especially at idle, while too little will cause noticeable crossover distortion, especially at low signal levels. 

            The amplifier circuitry must be cool, or at least within a couple degrees of ambient air temperature, and the top cover must be removed. If the driver and output transistors are significantly warmer than the ambient air, leave the amplifier off and let it cool before proceeding. Before turning the amplifier on to set bias on one or both channels, familiarize yourself with the locations of the trimpots (R131 and R231) and the voltage measuring points so you can work quickly but thoroughly. If the amplifier warms up before you finish setting the bias, you will need to shut the amplifier off and let it cool down before you resume.

Tools and resources you will need:
 
1. Small flat screwdriver (non-conductive) for adjusting trimpots
2. DC voltmeter
3. AC power

Procedure
 
1. Turn the amplifier’s gain controls all the way down. No test signal is needed.
2. Plug the amplifier into an appropriate AC source. Turn the amplifier on.
3. Channel 1: While measuring the DC voltage across resistor R146, adjust trimpot R131 to obtain the voltage listed in Table 1.
4. Channel 2: While measuring the DC voltage across resistor R246, adjust trimpot R231 to obtain the voltage listed in Table 1.
After setting the bias, calibrate the positive and negative current limiting; instructions for the procedure follow below

Setting positive and negative current limits

Tools and resources you will need
 
1.Oscilloscope

2. 2-ohm resistive load (rated for at least 1200 watts)

3. Shorting connector for amplifier output

4. Variable AC transformer (e.g., Variac, Powerstat, etc.) rated for 25A (120V) or 12A (230V). Make sure the AC supply is appropriate for the amplifier.

5. 1 kHz audio sine wave generator

6.  Digital multimeter

7. Clamp-on digital current meter (e.g., Fluke 30 Clamp Meter)

8. Small flat screwdriver (nonconductive) for adjusting trimpots

Procedure
1. Set the audio sine generator to 1 kHz at 1 volt RMS and connect it to Channel 1's input. Connect a 2-ohm load and the oscilloscope probe across Channel 1's output.
2. Turn up Channel 1's gain control partway. On the oscilloscope you should see the amplitude of the sine wave increase accordingly.
3. Turn the gain control back down and apply a short circuit across the output terminals of Channel 1. Clamp a current probe either onto one of the brown wires running to the AC switch or onto
4. Turn the gain control all the way up. Adjust trimpots R139 and R140 equally until the current measured falls within the range shown in Table below.
5. Turn the gain control all the way down and remove the short circuit so the channel drives the 2-ohm load. Turn the gain control back up until the output clips. The voltage at which the signal starts to clip should fall within the range shown in Table below. If the clipping is asymmetrical, that is, the signal clips on either the positive or negative side first, adjust R139 to make it symmetrical.
6. Turn the gain control down. If the amp has begun to warm up shut it off and let it cool a few minutes before proceeding with Channel 2.

7. Repeat steps 1 through 5 for Channel 2. Use trimpots R239 and R240 to adjust the current limiting in steps 11 and 12.
8. Turn both channels’ gain controls all the way down. Clamp the ammeter onto one of the amp’s AC wires and check the amp’s idle current. If the amplifier is still at about room temperature, the idle current should match the value shown in Table below.

BIAS TABLE FOR RMX 850

TREADMILL TIPS


                     

                                   TREADMILL TIPS

BELT LOSES POWER
This condition is when the treadmill operates normally without a person on the belt and then slows down when someone steps on the belt or when the treadmill operates normally for a given period of time with someone on the belt then abruptly begins to slow down.
There are four typical causes for this problem (listed in order of our experience:
1) The walking belt and/or deck are worn. (85% of the time)
2) The walking belt and/or motor belt are too tight- if you have adjusted either recently. (8% of the time)
 3) The motor has lost torque and needs brushes or has demagnetized or has developed high resistance. (5% of the time)
4) The controller is dropping output. (2% of the time)

Walking Belt is Worn: 
The only certain way to test for a worn walking belt is to take a DC amp draw (if you have a DC treadmill) or an AC draw (for AC). Trying to look at the belt or a feel test is highly unreliable. Better tests, if you lack a DC ammeter (they are expensive for a good one), are a coast test or an incline test. To test the deck, go back to the Troubleshooting section and download the belt and deck inspection instructions. The coast test is to get on the treadmill as the lowest incline setting and walk on the treadmill at 3 MPH. Pull the safety key and it should take you 2-3 full steps to stop (this is a general rule…some like a few Tunturi models stop on a dime even with a healthy belt but for most models, this tests works well upon). Fewer steps indicate high friction. The incline test is to put the treadmill at max incline and walk on it at 3 MPH. If the treadmill operates normally at max incline but bogs down at minimum incline, replace the walking belt. Gravity takes over for the drive system eliminating much of the friction problem. On some heavily worn walking belts, this test will not eliminate the problem.
Walking Belt/Motor Belt too Tight: 
If you have adjusted the walking belt or motor belt recently, check for this problem. When the belts start slipping, some people just crank down the belts and on treadmills, tighter is not necessarily better. The tighter the belts, the more the drive system has to work to keep everything moving. You should be able to lift the walking belt (with the treadmill unplugged) in the center of the treadmill about 2-3” without straining. Tighter belts should be loosen but make sure you don’t create a dangerous slipping situation by loosening.
The motor belt (with the treadmill unplugged) should be able to be turned by hand to almost a 90 degree angle from its normal operating position. Loosen the belt if too tight. Make sure to test for slipping and if it does with the proper tension, replace the motor belt.

Needs Brushes / Demagnetized Motor / Resistance Problem:

                Typically when we find a motor that has lost torque; it needs a new set of motor brushes. Typically we can make brushes for almost any motor if we don’t already stock them. Motor demagnetization is not that common but it does happen and it is normally easy to diagnose. If you have confirmed the belt and/or deck is not worn and the belts aren’t too tight, you can test for a motor torque problem. DO NOT USE YOUR HAND OR ANY OTHER BODY PART TO IMPEDE THE MOTOR…YOU WILL LIKELY LOSE YOUR BODY PART IN THE PROCESS IF THE MOTOR IS GOOD. The step to test for the motor is to use a foreign object preferably on a long shaft. First determine the direction of the motor spin (most have directional movement printed on the motor tag), then apply pressure with an object with downward pressure on the flywheel in the direction the flywheel is turning (do not attempt to put force against the rotating direction of the flywheel as you can easily injure yourself). If you can slow the motor, typically you need brush replacement. To test for demagnetization, the motor must be disassembled. Once you have the motor retaining bolts removed, remove the motor core by sliding it out of the end of the housing. If the magnets pull the core against the housing and it is difficult to remove, the magnets are good. If the magnets do not attract the core, the motor has to be replaced. To test for high resistance on DC motors, you must use a multi-meter for accurate testing. Put a test lead in the positive lead (usually red) and the other in the negative lead (usually black) and then set the meter to the ohms scale. Readings that are normal are between 1 and 2. Some small motors will have higher readings and larger motors have lower readings. Readings above the normal range indicate you have high resistance in the motor and we have seen them incredibly high. Since the copper flexes every time it energizes, the ability of the windings to conduct electricity is reduced over time. Large motors typically are more cost efficient to have rewound. Smaller motors are typically cheaper to replace.

Controller:
This is the most uncommon of the causes. Typically replacing a controller in this situation will not solve the underlying problem and then you will end up replacing a belt as well as a control. Normally if a control is dropping output, it will do it with a person on the belt or not. Tests of DC output dropping is normal in many controls since they have a current limiter which will automatically drop output to prevent burning up the board. This is best diagnosed by eliminating the other possible problems first. If you are left with the control as the cause, replace the control.

Walking Belt Friction Problems

 As the walking belt wears, it creates more friction with the deck which creates more heat in the belt causing it to wear further. Additionally, the increased friction requires the motor to work harder to keep the belt moving at the same speed. With this in mind, it causes the motor to draw more electricity and therefore, more power to move the belt. 

The motor has to get rid of this excess energy in some way so the way it normally does it is by releasing it in heat so that's why treadmills with belt problems typically overheat the motor too. All of this to say that if the breaker starts tripping, you know that the belt is causing the motor to pull too many amps and the safety system is working as it should. If the breaker has tripped more than a few times, it will need to be replaced because the breaker weakens every time it trips. Additionally, the walking belt will need to be lubricated at a minimum and if you want to be very aggressive toward the symptoms, replace the walking belt. 

WHY USE TREADMILL BELT CLEANER?

             If your treadmill is properly maintained, you should not have to clean the backing of the belt, unless it is in a normally dirty area (we recommend that you keep your treadmill out of these areas). What you must do to the backing of the belt is lubricate it. We have formulated a lubricant (World Famous Treadmill Lube) that has an agent that actually repels dirt from the underside of the belt. It also has another agent that has a high heat constant which means it takes more energy to heat it up (that keeps the heat lower). So, if you keep it maintained (cleaning, etc.) and lubricated, you shouldn't have a problem with dirt on the underside of the belt. To understand why to use belt cleaner, you first have to understand the dynamics of a conveyor belt driven system. Most home treadmills have a DC controller attached to a DC motor which is belt driven to a front roller which is a belt driven conveyor system. Walking or running on this conveyor system creates heat (from the friction of the belt backing). If you have too little friction, the treadmill will not operate properly (the most evident problem is on an incline the treadmill will keep speeding up). The energy exchange process creates heat. 

The pressure that is exerted against this system from the user, for the average person, equals hundreds of thousands lbs. of pressure every mile. In other words, no matter what the lubricity of the belt is, the potential for heat build up is great. If you combine this with a nice layer of dirt on the top of the belt (acting as an insulator) your heat constant will certainly rise. Removing the dirt layer from the top of the belt helps reduce belt heat and thereby lowers the amp draw requirements of the DC electrical system. This helps the controller and motor run cooler in addition to the heat level of the belt. We have tested treadmills before and after belt cleaning and have seen a 20% reduction in the amp draw of the unit. This could be a major contributor to the longevity of the

1) motor brushes 
2) armature of the motor 
3) DC motor controller.

Since heat is also an enemy of the walking belt and deck, lower operating temps can also extend their life. You don't have to have our belt cleaner to clean your belt. Another way to clean it is to use water and a nylon bristle brush. Make sure to let the belt completely dry before using it again and don’t get water underneath the walking belt.