I should know better by now than to take on power amps for repair....
I've got a pair of these Denon POA-S10 monoblocks- both had bias issues due to the Bias transistor TR221 being installed in reverse orientation.
I replaced the k2013/j313 pair with IRF610/9610 in both amps as they were verified tested bad when i caught the issue with the c4137 and now the one unit is working better than new. Both units had a complete re-cap of all 'lytics.
The problem unit was also powered up for a short time with the output shorted to ground- pre-protection relay. After the swaps it's idling stupidly high at the lowest trimmer setting (like +160mv at the test points, and the amp is drawing 2.5A, and it will intermittently oscillate at ~100kHz- which I think is a symptom not a cause.
I've replaced D221,222,223,224 and the Zeners at 213 and 214 which actually seemed to bring the 'off-load' voltages with TR211/212 removed nearly in line with the working PCB, but still no change to the overall issue when everything is hooked up as expected.
I've (mostly) verified that the issue is NOT in the output devices (TR213-218) or the mosfets at TR211/212, or the PSU or output boards because i swapped the Power amp PCB from the working unit to the chassis of this one and it works beautifully. So i'm working on the assumption that the issue is on this board. But even after shotgunning everything in the bias circuit (and some of the feedback components when i was chasing the oscillation) there's basically no change. I'm tearing out my hair! Solid state power amps are not generally in my wheelhouse but this is for a good friend. Any suggestions, ideas, very welcome!
Attached annotated schematic- Green are voltages that are verified in spec, Blue and yellow are components that have been replaced with direct subs or equivalents as noted.
I've got a pair of these Denon POA-S10 monoblocks- both had bias issues due to the Bias transistor TR221 being installed in reverse orientation.
I replaced the k2013/j313 pair with IRF610/9610 in both amps as they were verified tested bad when i caught the issue with the c4137 and now the one unit is working better than new. Both units had a complete re-cap of all 'lytics.
The problem unit was also powered up for a short time with the output shorted to ground- pre-protection relay. After the swaps it's idling stupidly high at the lowest trimmer setting (like +160mv at the test points, and the amp is drawing 2.5A, and it will intermittently oscillate at ~100kHz- which I think is a symptom not a cause.
I've replaced D221,222,223,224 and the Zeners at 213 and 214 which actually seemed to bring the 'off-load' voltages with TR211/212 removed nearly in line with the working PCB, but still no change to the overall issue when everything is hooked up as expected.
I've (mostly) verified that the issue is NOT in the output devices (TR213-218) or the mosfets at TR211/212, or the PSU or output boards because i swapped the Power amp PCB from the working unit to the chassis of this one and it works beautifully. So i'm working on the assumption that the issue is on this board. But even after shotgunning everything in the bias circuit (and some of the feedback components when i was chasing the oscillation) there's basically no change. I'm tearing out my hair! Solid state power amps are not generally in my wheelhouse but this is for a good friend. Any suggestions, ideas, very welcome!
Attached annotated schematic- Green are voltages that are verified in spec, Blue and yellow are components that have been replaced with direct subs or equivalents as noted.
