Has anyone seen one of these?
This amp is using 7-legged devices in the PS, though legs 2,3, 5, 6,7 are all tied together on the PCB. I have not seen FETs like this before if they are even fets.
The amp only briefly powers for 1/4 second and displays amber LEDs on the pre-amp board. I believe that is in protection but not fully sure.
There is PS drive on the gates of these strange fets for the brief moment. Nothin shorted in the amp. I was thinking maybe removing the main rectifiers to see if the PS side will fully power up.
Otherwise I guess I'll ask; is there a schematic for this amp by chance?
The amp seems to not be making proper negative rail voltage at D21, and D22. I'm 95% sure both of these rectifiers are duds.
This amp is using 7-legged devices in the PS, though legs 2,3, 5, 6,7 are all tied together on the PCB. I have not seen FETs like this before if they are even fets.
The amp only briefly powers for 1/4 second and displays amber LEDs on the pre-amp board. I believe that is in protection but not fully sure.
There is PS drive on the gates of these strange fets for the brief moment. Nothin shorted in the amp. I was thinking maybe removing the main rectifiers to see if the PS side will fully power up.
Otherwise I guess I'll ask; is there a schematic for this amp by chance?
The amp seems to not be making proper negative rail voltage at D21, and D22. I'm 95% sure both of these rectifiers are duds.
Yes thats probably the one. PS Fets seem to be OK.
I replaced the rectifiers which were MUR1620CT/CTG but the amp still cycles. My guess is these rects originally failed because they were being hammered on/off every second. Rail voltage is getting to +-48vDC now. Regulated voltage looks good about +-15vDC. I tried powering the amp with neither pre-amp board and no different. Pulse/cycles about every second. Nothing getting hot and nothing really jumping out at me as failed.
The amp is using IRS20957S for output drivers for each of the 4 channels. The output fets appear to have proper voltages on legs. No significant resistance on any caps near the IRSs. No DC on any speaker terminal.
A modified Type 3 is my guess at this. I need to do more research...
I replaced the rectifiers which were MUR1620CT/CTG but the amp still cycles. My guess is these rects originally failed because they were being hammered on/off every second. Rail voltage is getting to +-48vDC now. Regulated voltage looks good about +-15vDC. I tried powering the amp with neither pre-amp board and no different. Pulse/cycles about every second. Nothing getting hot and nothing really jumping out at me as failed.
The amp is using IRS20957S for output drivers for each of the 4 channels. The output fets appear to have proper voltages on legs. No significant resistance on any caps near the IRSs. No DC on any speaker terminal.
A modified Type 3 is my guess at this. I need to do more research...
4 channels all measuring the same way. G-S measuring 3M-15M. G-D measuring 20K on the high side fets and 3.5M on the low side fets. All 4 channels similar.
OK there may be something wonky in the PS section of this amp still. I was wondering why the amp was pulling 0.07A without REM, and just found the 1n5402 polarity protection diode cracked and shorted at 35 ohms. I replaced it and now amp draws 0.00A without REM but the amp still has the same cycling problem. So, this amp seems to have suffered reverse connect.
I'll check more in reference to that image as well now.
I'll check more in reference to that image as well now.
Ohming out the 4x IRS20957S. All 4 are the same readings and seem to be OK. The lowest reading was 21k from HO to VS. Outputs are still in circuit. All seem to be ok there too.
CSD on all 4x 20957s have 1vDC on them when powered, and peak hold on the meter shows pulse out to 1.8vDC every second. Then when I remove all power to the amp; CSD goes straight to 10.5vDC after a 5 second count and then falls to zero after about 10 seconds.
Look at them with the scope on 2v/div.
Is one of the 4 pulsing with a bit more amplitude than the other 3?
Is one of the 4 pulsing with a bit more amplitude than the other 3?
All 4 pulsing identically. Scope is pulsing out to about 4.1v on each. It is like a flash wave though. Maybe only a few cycles. Barely visible on the scope.
Can you find the circuit that's driving the CSD terminals?
If you can, disable it to see if the amp powers up.
If you can, disable it to see if the amp powers up.
The CSD terminals are connected each to 2 diodes such as example D107 and D108. Each channel has a pair of diodes, and the on the opposite sides of these diodes they're all connected. From there, the diodes are connected back to U19 which is an LM393. I replaced U19 and also tried powering the amp without it but same result of cycling. With U19 removed, CSD terminals receive a much higher pulse voltage of about 12vDC
Attachments
Still pulsing with the 393 removed?
When the voltage on the CSD terminals goes higher. do you see any oscillation on the outputs?
When the voltage on the CSD terminals goes higher. do you see any oscillation on the outputs?
Still pulsing without the 393. Oscillation is on the outputs except when there is a pulse.
Unfortunately I was testing oscillation on the very last output FET and my probe happened to slip but made no spark against C123 in the above photo. Now I believe that IRS20957 has failed and I dont have a spare.
Unfortunately I was testing oscillation on the very last output FET and my probe happened to slip but made no spark against C123 in the above photo. Now I believe that IRS20957 has failed and I dont have a spare.
Were you seeing rail-rail oscillation on the outputs with the low-amplitude pulsing when the 393 was in the circuit?
When is there oscillation, when the CSD is high or when it's low?
When is there oscillation, when the CSD is high or when it's low?