This is a 6 channel amp where the right subwoofer channel blew, but the rest of the amp still worked before the repair. I found both IRF540 in the channel blown (Q613 & Q614), as well as the following:
Q609, Q610, Q611, Q612
Q605, Q606, Q603, Q602
R633, R634, R615, R624, All four 0.22ohm emitter resistors, and the 200 ohm resistor right next to the emitter resistors.
I cant get this amp to power up without the current limiting resistor. Q614 gets hot after about 30 seconds of limiting current. For the first few seconds, theres DC voltage on the infected channel's speaker terminals.
Theres larger than average voltage across emitters of Q614 ~0.014
Q609, Q610, Q611, Q612
Q605, Q606, Q603, Q602
R633, R634, R615, R624, All four 0.22ohm emitter resistors, and the 200 ohm resistor right next to the emitter resistors.
I cant get this amp to power up without the current limiting resistor. Q614 gets hot after about 30 seconds of limiting current. For the first few seconds, theres DC voltage on the infected channel's speaker terminals.
Theres larger than average voltage across emitters of Q614 ~0.014
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If the outputs are out of circuit in the affected channel the amp should power up without drawing excessive current. I own one of these that came to me much the same condition as yours.
To simplify my efforts I just gutted both bass channels and then realigned the bias's in each channel after it was able to power up without issues.
The bias control is not connected to the outputs like most Mosfet amps its part of the input diff pairs and I always found those transistors badly damaged on this series of amp when a channel failure had occurred.
My experience with these XS amps is that when they fail like yours has there are damaged components from input to output, and only on rare instances was it possible to get these repaired by simply replacing outputs and gate drivers.
Also any excessive DC on the speaker terminals above 10 to 15 mvdc is a indicator that the input pair are damaged. There are only MPSA-06 and MPSA-56 and a couple 2SC2389 < input diff pair> transistors, but you should also pay close attention to the 1n4148 and associated zeners in the heart of the circuitry. They tend to be way out of spec also after such a hard failure.
Zeners are ; D607 and D608 and they are 15 volt 1N5245B. Zeners D605 and D606 are 6.0 volt 1N5233B. Q604 is the bias control transistor and it gets it -22 volts and bias connection from the Lm339 IC back in the 12 volt side, and Q600 is sink mounted and it is supplied +34 volts from the bass power supply to Q602 and Q603, and Q605 and Q606. This is also the mute circuit for each channel.
PG made this amp very economical to repair cost wise, but in 95% of the failures the whole channel needs to replaced to get like new functionality. As I said I have one right here at my feet in fact under my bench, and it was much like yours when I got it. I suggest you pull all the outputs out of the sub channels, then the amp will turn on without using a current limiter in the supply side.
Resistors are 2% as I recall 1/8 watt except on the output. If you can't read then I can ID them for you. Output rails should be +&-28 volts DC and the front end gets +34 and -22 across that circuitry, all from the sub power supply section, the other four channels are on a separate power supply....Let me know what else you need to know, I will gladly get the info for you....
To simplify my efforts I just gutted both bass channels and then realigned the bias's in each channel after it was able to power up without issues.
The bias control is not connected to the outputs like most Mosfet amps its part of the input diff pairs and I always found those transistors badly damaged on this series of amp when a channel failure had occurred.
My experience with these XS amps is that when they fail like yours has there are damaged components from input to output, and only on rare instances was it possible to get these repaired by simply replacing outputs and gate drivers.
Also any excessive DC on the speaker terminals above 10 to 15 mvdc is a indicator that the input pair are damaged. There are only MPSA-06 and MPSA-56 and a couple 2SC2389 < input diff pair> transistors, but you should also pay close attention to the 1n4148 and associated zeners in the heart of the circuitry. They tend to be way out of spec also after such a hard failure.
Zeners are ; D607 and D608 and they are 15 volt 1N5245B. Zeners D605 and D606 are 6.0 volt 1N5233B. Q604 is the bias control transistor and it gets it -22 volts and bias connection from the Lm339 IC back in the 12 volt side, and Q600 is sink mounted and it is supplied +34 volts from the bass power supply to Q602 and Q603, and Q605 and Q606. This is also the mute circuit for each channel.
PG made this amp very economical to repair cost wise, but in 95% of the failures the whole channel needs to replaced to get like new functionality. As I said I have one right here at my feet in fact under my bench, and it was much like yours when I got it. I suggest you pull all the outputs out of the sub channels, then the amp will turn on without using a current limiter in the supply side.
Resistors are 2% as I recall 1/8 watt except on the output. If you can't read then I can ID them for you. Output rails should be +&-28 volts DC and the front end gets +34 and -22 across that circuitry, all from the sub power supply section, the other four channels are on a separate power supply....Let me know what else you need to know, I will gladly get the info for you....
1moreamp,
I checked through all those components and was not able to locate any more defects. Do you happen to have any recomendations for voltage measurements?
I removed the outputs in the defective sub channel; the amp will power and play on all other 5 channels (Even the 'other' sub channel).
I checked through all those components and was not able to locate any more defects. Do you happen to have any recomendations for voltage measurements?
I removed the outputs in the defective sub channel; the amp will power and play on all other 5 channels (Even the 'other' sub channel).
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