I'm going to see if there is something in the shop that I can get working well enough to check a few things. These amps have been so simple to repair that I haven't done much testing.
As a side note, one of the few problems I've had other than outputs or the 1D transistors (in the audio section) is the op-amp on the top corner of the driver board. You may want to try replacing it.
As a side note, one of the few problems I've had other than outputs or the 1D transistors (in the audio section) is the op-amp on the top corner of the driver board. You may want to try replacing it.
The thing is, I took an audio driver board from a working amp and installed it, the same problem with this amp. The driver board that I refurbished with new 1D and 2D transistors is working properly in the other amp. So the driver board that is in the amp right now is a known good working board.
I thought there might have been a bad connection with the audio driver transistors but I removed them, double checked all connections and reinstalled them. The C2690 and A1220 driver transistors are brand new from Mouser, and the IRF640N outputs are brand new also.
I am stumped at this point.
I thought there might have been a bad connection with the audio driver transistors but I removed them, double checked all connections and reinstalled them. The C2690 and A1220 driver transistors are brand new from Mouser, and the IRF640N outputs are brand new also.
I am stumped at this point.
Have not found any disconnections from the output drivers to the driver board, or the output transistors themselves.
Amp powers up and idles continuously with 62v of + and - rail voltage, but as soon as a load/speaker is connected, the - rail starts to climb upwards.
PS FETS replaced, outputs replaced, output drivers replaced, ps and output driver cards swapped for known good ones... Don't know what else to check.
Is there any other part I can check or change?
Amp powers up and idles continuously with 62v of + and - rail voltage, but as soon as a load/speaker is connected, the - rail starts to climb upwards.
PS FETS replaced, outputs replaced, output drivers replaced, ps and output driver cards swapped for known good ones... Don't know what else to check.
Is there any other part I can check or change?
What is happening is that when measured with a multimeter with the black probe on the ground terminal of the amp, I get +62v and - 62v on the rails with no speaker or load connected to the output terminals.
As soon as I connect a speaker to the terminals, the reading for the negative rail starts to increase upwards without stopping. I have not let it increase much past -80v before removing the remote power as the capacitor on the negative rail vented when tested after the initial repair. The +62v drops to about +60 or +61v and remains there during this occurrence.
I assume this same issue was occurring but I didn't pick up on it until the capacitor failure. The capacitors are 100v so I assume the voltage climbed past - 100v. I also have replaced all 4 rail capacitors.
As soon as I connect a speaker to the terminals, the reading for the negative rail starts to increase upwards without stopping. I have not let it increase much past -80v before removing the remote power as the capacitor on the negative rail vented when tested after the initial repair. The +62v drops to about +60 or +61v and remains there during this occurrence.
I assume this same issue was occurring but I didn't pick up on it until the capacitor failure. The capacitors are 100v so I assume the voltage climbed past - 100v. I also have replaced all 4 rail capacitors.
I am also certain that it is a drive problem but I don't know how to troubleshoot and diagnose the source of it.
I took some readings from another amp of similar design, that uses the same driver board, output drivers and outputs. On the gates of the outputs, there was almost 4v on both positive and negative outputs. On this one, there is no drive voltage on the gates of the negative outputs, and only 1.8v on the positive gates. The negative output gate legs have the same voltage reading as the drain legs, so no positive drive voltage.
I took some readings from another amp of similar design, that uses the same driver board, output drivers and outputs. On the gates of the outputs, there was almost 4v on both positive and negative outputs. On this one, there is no drive voltage on the gates of the negative outputs, and only 1.8v on the positive gates. The negative output gate legs have the same voltage reading as the drain legs, so no positive drive voltage.
I found the R-GND and the C-GND in between the transformers. There is a solid metal jumper connecting the pads over the resistor shaped outline on the board. I assume this means that it is directly connected from factory?
The audio driver board voltages at idle are:
1) - 62.56
2) - 61.91
3) - 61.92
4) 1.49
5) 1.35
6) 77.34
7) 0.00
8) 0.00
9) - 15.11
10) 14.83
11) 0.14
PIN3: What voltage should be on pin3 of the audio driver board? It is listed on the schematic as -rail+12v. Does that mean that I should be seeing - 50v on this pin? Rail of - 62, taking away +12, leaving - 50?
PIN10: My +15v is only +14.83,is that OK?
I am assuming my problem lies with PIn3 or PIn4 as the other inputs appear close enough to what they are supposed to be, and the outputs can't be faulted if the input is wrong. The driver board is known good as it was swapped from a perfectly working amplifier. I don't know enough about Pin3 and Pin4 to diagnose further.
I measured the voltage on L7812 since this feeds Pin3 and I got:
Gate: - 42. 6
Source: - 62.5
Drain: - 61.8
The audio driver board voltages at idle are:
1) - 62.56
2) - 61.91
3) - 61.92
4) 1.49
5) 1.35
6) 77.34
7) 0.00
8) 0.00
9) - 15.11
10) 14.83
11) 0.14
PIN3: What voltage should be on pin3 of the audio driver board? It is listed on the schematic as -rail+12v. Does that mean that I should be seeing - 50v on this pin? Rail of - 62, taking away +12, leaving - 50?
PIN10: My +15v is only +14.83,is that OK?
I am assuming my problem lies with PIn3 or PIn4 as the other inputs appear close enough to what they are supposed to be, and the outputs can't be faulted if the input is wrong. The driver board is known good as it was swapped from a perfectly working amplifier. I don't know enough about Pin3 and Pin4 to diagnose further.
I measured the voltage on L7812 since this feeds Pin3 and I got:
Gate: - 42. 6
Source: - 62.5
Drain: - 61.8
Yes. Pin 3 should be 12v above the negative rail.
+14.83 is OK
The The 7812 appears to be damaged. Look up the datasheet. It's not an FET. The terminals are
Input
Ground
Output
The ground is on the negative rail. To make troubleshooting simpler, it's best to check the regulators by placing the black probe on its ground terminal. The other terminals will read approximately 20v and 12v when the regulator is working properly.
Pin 4 should read 1 ohm to the output filter inductor. Place one meter probe on the header on the driver board (not on a point on the main board) so that you're confirming that there is a good connection to the driver board at the same time.
+14.83 is OK
The The 7812 appears to be damaged. Look up the datasheet. It's not an FET. The terminals are
Input
Ground
Output
The ground is on the negative rail. To make troubleshooting simpler, it's best to check the regulators by placing the black probe on its ground terminal. The other terminals will read approximately 20v and 12v when the regulator is working properly.
Pin 4 should read 1 ohm to the output filter inductor. Place one meter probe on the header on the driver board (not on a point on the main board) so that you're confirming that there is a good connection to the driver board at the same time.
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