Working on one of these at the moment.
Currently what it is doing is it seems to work correctly from a cold start up powered through 1 ohm current limiting resistor. It draws ~3.2A which seems about appropriate. I have very low DC offset and good audio signal out. All looks good.
If I shut the amp down with the remote lead and restart it, it draws ~8.5A and I have a little DC offset, ~.450VDC between secondary CT and one output inductor and ~.950VDC on the other output inductor. Relay does not engage but it does not light up the protection LED, the green LED is lit. My power supply sags down several volts.
It does need some time even after I shut down my power supply and try to restart it.
What I have done;
Rebuilt the power supply.
Replaced two banks of five IRF9640 gate resistors were fine.
Replaced one bank of three FB31N20, gate resistors were fine.
Removed both audio driver boards to check for any damaged components and found none suspect even removing the specific drivers to the banks of outputs that failed to verify no leakage. One Ohm resistors are good, the diodes checked OK.
With both audio driver boards out, the amp powered up every time I wanted it to drawing ~1.5A
Verified Rail to Rail.
Verified expected signals and voltages on the LM361.
Found a missing resistor at R168 and installed a 2.2K Ohm one there. R168 connects between the KIA431 and the C1027, see pic.
However, upon typing this, I decided to check the voltage drop on the two Zener diodes that I can easily reach and one of them is out of tolerance (~9.5V) when the amp is working correctly. I am going to look for a replacement, in the meantime is there something else going on that may cause these symptoms?
Currently what it is doing is it seems to work correctly from a cold start up powered through 1 ohm current limiting resistor. It draws ~3.2A which seems about appropriate. I have very low DC offset and good audio signal out. All looks good.
If I shut the amp down with the remote lead and restart it, it draws ~8.5A and I have a little DC offset, ~.450VDC between secondary CT and one output inductor and ~.950VDC on the other output inductor. Relay does not engage but it does not light up the protection LED, the green LED is lit. My power supply sags down several volts.
It does need some time even after I shut down my power supply and try to restart it.
What I have done;
Rebuilt the power supply.
Replaced two banks of five IRF9640 gate resistors were fine.
Replaced one bank of three FB31N20, gate resistors were fine.
Removed both audio driver boards to check for any damaged components and found none suspect even removing the specific drivers to the banks of outputs that failed to verify no leakage. One Ohm resistors are good, the diodes checked OK.
With both audio driver boards out, the amp powered up every time I wanted it to drawing ~1.5A
Verified Rail to Rail.
Verified expected signals and voltages on the LM361.
Found a missing resistor at R168 and installed a 2.2K Ohm one there. R168 connects between the KIA431 and the C1027, see pic.
However, upon typing this, I decided to check the voltage drop on the two Zener diodes that I can easily reach and one of them is out of tolerance (~9.5V) when the amp is working correctly. I am going to look for a replacement, in the meantime is there something else going on that may cause these symptoms?
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I replaced the diode that was reading ~9.5V with a new 4742 and it still reads ~9.5V across it.
It is because my power supply is sagging a bit, if I turn it up so there is >12V on the B+ and ground terminals, I get ~12 across that diode then so that's a non-issue.
It is because my power supply is sagging a bit, if I turn it up so there is >12V on the B+ and ground terminals, I get ~12 across that diode then so that's a non-issue.
Well this seems a little bizarre. The amp will operate correctly (switching on and off) ~75% of the time if I turn it over so that I am not looking at the circuit board.
Twisting and turning either of the two transformers does not change anything when its in the high current draw state.
Twisting and turning either of the two transformers does not change anything when its in the high current draw state.
Are any of the heatsink mounted semiconductors getting hot when the amp is drawing greater current?
No, nothing was really getting hot, just my current limiting resistor. I left it in that state for several minutes looking for that.
Seems to be just fine. It powers up every time without the current limiter and does not blow a 10A fuse.
So, I am still sitting on this one.
Everything was working fine during testing up until I put it all back together, back cover and all. I went to test it again and it started to draw significant current and then went into protection. Now it had a shorted output from a new group not previously failed. A new set of 31N20D needed replaced. A little over a week later and I have the new ones.
I just got done replacing that set and going through all the same testing as before and put the back cover on to pop another one of the 31N20Ds from the exact same group.
I post this to save some time and effort for someone else. I circled a capacitor that the top of was touching the legs of the set of drivers causing the failure. There is not enough room in there to just bend it out of the way, so I put it on the other side of the board. This was probably a result from me removing the two driver boards earlier and I may not have put them back in their original location or with enough "tilt" away from that cap.
Amp is now working as it should fully assembled.
Everything was working fine during testing up until I put it all back together, back cover and all. I went to test it again and it started to draw significant current and then went into protection. Now it had a shorted output from a new group not previously failed. A new set of 31N20D needed replaced. A little over a week later and I have the new ones.
I just got done replacing that set and going through all the same testing as before and put the back cover on to pop another one of the 31N20Ds from the exact same group.
I post this to save some time and effort for someone else. I circled a capacitor that the top of was touching the legs of the set of drivers causing the failure. There is not enough room in there to just bend it out of the way, so I put it on the other side of the board. This was probably a result from me removing the two driver boards earlier and I may not have put them back in their original location or with enough "tilt" away from that cap.
Amp is now working as it should fully assembled.
