Bought the amp from ebay, seller did not make no secret of what was going on in the amp, still I decided to give it a try.
Amp is missing: RCA jacks, cooling fan (which is a critical part of this amplifier as I have heard), some PS caps, all PS FETs, most of their drivers, loads of resistors, rectifier, some of the big jumpers which connect PS FETs to ground and as a added bonus: FETs went out in flames and board is carbonized where they used to be and some traces do not exist anymore because of the heat.
I get a good signal on pads of power supply FETs drivers, so the first thing I will do is replace them, try to clean out the carbonized board, remove rectifiers, install PS FETs and see if I can get power supply running, any other recommendations?
Any idea what could have caused this kind of failure?
Amp is missing: RCA jacks, cooling fan (which is a critical part of this amplifier as I have heard), some PS caps, all PS FETs, most of their drivers, loads of resistors, rectifier, some of the big jumpers which connect PS FETs to ground and as a added bonus: FETs went out in flames and board is carbonized where they used to be and some traces do not exist anymore because of the heat.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
I get a good signal on pads of power supply FETs drivers, so the first thing I will do is replace them, try to clean out the carbonized board, remove rectifiers, install PS FETs and see if I can get power supply running, any other recommendations?
Any idea what could have caused this kind of failure?
Installed one IRFZ44N in each bank (4 in total), new rectifiers, 3 new PS caps. It was impossible to find the right size caps, I found a bit bigger caps, only a few millimeters but it made it quite difficult to fit them in the amp. I had to leave 3 old ones in at the moment. Amp does not draw excessive current. There is +/-60V on rectifiers center legs.
But there is no output on speaker terminals.
On one bank of outputs there was square on 2 legs and rail voltage on 1 leg.
On the other bank I see rail voltage on one leg, square on other and something weird on third leg.
Do they look right?
First picture is signal on speaker terminal, no input or input, output is the same.
2ms/0,1V.
Second picture is square on ouputs, 2us/10V.
Third picture is signal on third leg on one bank of outputs, 1us/10V.
I did not check signals on driver board, I checked the two drivers on the board which are likely to overheat and fail, they were not shorted but I will replace them anyway like Perrys tutorial suggests.
But there is no output on speaker terminals.
On one bank of outputs there was square on 2 legs and rail voltage on 1 leg.
On the other bank I see rail voltage on one leg, square on other and something weird on third leg.
Do they look right?
First picture is signal on speaker terminal, no input or input, output is the same.
2ms/0,1V.
Second picture is square on ouputs, 2us/10V.
Third picture is signal on third leg on one bank of outputs, 1us/10V.
I did not check signals on driver board, I checked the two drivers on the board which are likely to overheat and fail, they were not shorted but I will replace them anyway like Perrys tutorial suggests.
Attachments
Waveform which I did not get a lock on earlier:
This time settings are 1ms/10V.
In the tutorial one of the driver board outputs has similar waveform, so it is correct?
I did not have time to troubleshoot it further today, I had to put together Hifonics Brutus first, that is for a paying customer, SPL is mine at the moment.
Tomorrow I will try to trace input signal, see if it makes it to the driver board.
Shorted output filter inductor should cause the amp to draw current?
This time settings are 1ms/10V.
In the tutorial one of the driver board outputs has similar waveform, so it is correct?
I did not have time to troubleshoot it further today, I had to put together Hifonics Brutus first, that is for a paying customer, SPL is mine at the moment.
Tomorrow I will try to trace input signal, see if it makes it to the driver board.
Shorted output filter inductor should cause the amp to draw current?
Attachments
It looks OK.
If you're unsure about the output filter inductors, look at the signal on the terminals of the inductors. They are in series. The point on the board that connects the inductors should have exactly 1/2 of the amplitude of the square wave on the terminal that's connected to the FETs. The inductor terminal that's connected to the filter capacitors should have essentially no square wave visible (scope set to 5v/div or higher).
If you're unsure about the output filter inductors, look at the signal on the terminals of the inductors. They are in series. The point on the board that connects the inductors should have exactly 1/2 of the amplitude of the square wave on the terminal that's connected to the FETs. The inductor terminal that's connected to the filter capacitors should have essentially no square wave visible (scope set to 5v/div or higher).
Inductors are probably OK, waveforms are like you described.
From the tutorial I did not understand whether the input of the driverboard should have audio signal or already PWM.
I traced audio from RCA jacks and already on the second opamp IC102 there is no clean audio. Scope was grounded to RCA shield.
Only clear waveform I could find on that opamp is on the picture, that waveform was constant, no matter if input was 100 Hz sine or just music.
I replaced the opamp, just in case, but that made no difference.
Is it safe to say that output and PS are working correctly and the fault is in preamp/driver board?
Scope settings: 1V/1us.
From the tutorial I did not understand whether the input of the driverboard should have audio signal or already PWM.
I traced audio from RCA jacks and already on the second opamp IC102 there is no clean audio. Scope was grounded to RCA shield.
Only clear waveform I could find on that opamp is on the picture, that waveform was constant, no matter if input was 100 Hz sine or just music.
I replaced the opamp, just in case, but that made no difference.
Is it safe to say that output and PS are working correctly and the fault is in preamp/driver board?
Scope settings: 1V/1us.
Attachments
A Power Acoustic A3000db came in for repair. These are the voltages from the various ICs. I used the RCA shield as the reference. You can read the 3-5mv readings as 0v.
Let me know if you have trouble reading it. I was too lazy to type it out.
http://www.bcae1.com/temp/a3000db - AC voltages.jpg
Let me know if you have trouble reading it. I was too lazy to type it out.
http://www.bcae1.com/temp/a3000db - AC voltages.jpg
Found the problem. When I got the amp it was already disassembled, when I was searching for audio on opamps I turned the pots and tried different switch positions, but I did not notice that phase switch was missing, installed a switch in empty postition and now I get clean loud output even with only 4 PS FETs installed.
Now the tedious work: install remaining FETs replace MPSA42s, install fan etc.
Can you take measurements of the bracket on which the fan is mounted? I do not have one I have to make it myself, fan I bought looks like this:
40*40*10mm, also I have to modify the plug, it has three wires.
Now the tedious work: install remaining FETs replace MPSA42s, install fan etc.
Can you take measurements of the bracket on which the fan is mounted? I do not have one I have to make it myself, fan I bought looks like this:
An externally hosted image should be here but it was not working when we last tested it.
40*40*10mm, also I have to modify the plug, it has three wires.
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