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Sansui AU 517 with hum in both channels...

Might be a good idea to check all the grounds. After REALLY looking at the schematic, there are no common points between the channels I can see.
 
Ray Gianelli said:
Might be a good idea to check all the grounds. After REALLY looking at the schematic, there are no common points between the channels I can see.
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This may be a dumb question but when you suggest checking grounds, is that just for continuity or is there something else I should be looking for?
 
jonah1979 said:
This may be a dumb question but when you suggest checking grounds, is that just for continuity or is there something else I should be looking for?
Click to expand...
Sorry, I read this but didn't reply and promptly forgot about it.

It's probably not the root cause, but tighten any screws used as grounds, and check any solder joints.
 
jonah1979 said:
This may be a dumb question but when you suggest checking grounds, is that just for continuity or is there something else I should be looking for?
Click to expand...
To expound a little (is that an oxymoron?) on Ray's comment about the grounds, did you un-solder any ground wires or maybe forget to re-attach any ground screws during your recent work? I think there's a ground screw that sits between the two amp channelson the bottom side of the chassis that provides signal ground for both amp channels. If that's not tight or is dangling, you'll likely hear hum.
 
I was out of town for a wedding and sat with the amp last night. As per your observation @Ray Gianelli TR04 was shorted. I replaced TR04 and TR03 to keep things symmetrical AND replaced their mating transistors TR01 and TR02 with modern equivalents (parts below).

TR01 and TR02: 2SD438 (Replacement: KSC2383)
TR03 and TR04: 2SB560 (Replacement: KSA1013)

I also double-checked all of the grounds, and everything seemed tight.

All to say - and great news - the hum is gone. It seemed that the short in TR04 was the culprit and created issues within the PS and rectification. Voltages in the PS are in line with the schematic and happily listening to the amp as I type this.

Thanks for all of your help!
 
jonah1979 said:
I was out of town for a wedding and sat with the amp last night. As per your observation @Ray Gianelli TR04 was shorted. I replaced TR04 and TR03 to keep things symmetrical AND replaced their mating transistors TR01 and TR02 with modern equivalents (parts below).

TR01 and TR02: 2SD438 (Replacement: KSC2383)
TR03 and TR04: 2SB560 (Replacement: KSA1013)

I also double-checked all of the grounds, and everything seemed tight.

All to say - and great news - the hum is gone. It seemed that the short in TR04 was the culprit and created issues within the PS and rectification. Voltages in the PS are in line with the schematic and happily listening to the amp as I type this.

Thanks for all of your help!
Click to expand...
I was chagrined that I didn't focus on the dual power supply earlier. But one thing I've learned over the years is that if you find a problem, fix it. Even if you don't think it's causing your trouble. Because many times it is.
Glad you got it sorted out!
 
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