Julian12345
Active Member
Hey team
I'm working on my friend's Pioneer SX-440 and trying to work out why I'm getting low voltages.
You can see in the attached doc I'm down on volts especially on pin 2 that should be 42v. Not sure why. I've tested the transistors on this board and are OK. I checked the diodes too and seem to check out OK but replaced them (the SD-1/SE-05 spec, not the Zener 1S337 though, I don't have one) with 1n4007's at any rate because I had some nearby and other's on other forums had done the same.
I have 35.7v at the filter capacitor.
Also recapped the PSU, filter and amp carefully.
Checked the outputs for shorts, and output trans tested well on diode mode in DMM
I checked all the transistors on the main amp board, tested OK. BUT if you suspect an issue send me back to dive deeper.
I'm not sure where to check idle current. I've put the DMM across emitter resistors but seem to get 0.02 ish volts on one channel and something like 0.3v on the other which seems whack. Both channels will distort at full volume but one of them is weaker and distorts much earlier, like half volume at best. Music via headphones sounds just fine, really good actually, even no balance issues and no distortion.
Radio works well
Would someone mind pointing out on the photo attached of the underside exactly where I should test for idle current? I think I have it wrong perhaps.
It's in really nice condition this unit so can't imagine it's totally whacked.
I know there's a lot of posts on this amp and I have read some of them but the PSU issue has prompted me to start this thread.
Thanks heaps!
Julian
I'm working on my friend's Pioneer SX-440 and trying to work out why I'm getting low voltages.
You can see in the attached doc I'm down on volts especially on pin 2 that should be 42v. Not sure why. I've tested the transistors on this board and are OK. I checked the diodes too and seem to check out OK but replaced them (the SD-1/SE-05 spec, not the Zener 1S337 though, I don't have one) with 1n4007's at any rate because I had some nearby and other's on other forums had done the same.
I have 35.7v at the filter capacitor.
Also recapped the PSU, filter and amp carefully.
Checked the outputs for shorts, and output trans tested well on diode mode in DMM
I checked all the transistors on the main amp board, tested OK. BUT if you suspect an issue send me back to dive deeper.
I'm not sure where to check idle current. I've put the DMM across emitter resistors but seem to get 0.02 ish volts on one channel and something like 0.3v on the other which seems whack. Both channels will distort at full volume but one of them is weaker and distorts much earlier, like half volume at best. Music via headphones sounds just fine, really good actually, even no balance issues and no distortion.
Radio works well
Would someone mind pointing out on the photo attached of the underside exactly where I should test for idle current? I think I have it wrong perhaps.
It's in really nice condition this unit so can't imagine it's totally whacked.
I know there's a lot of posts on this amp and I have read some of them but the PSU issue has prompted me to start this thread.
Thanks heaps!
Julian
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