Sansui 881 Hel Needed

JohnChi

New Member
Hi everybody. Question on my Sansui 881. Thanks to the experts here (dr. Audio) I was able to cure the low volume speaker hum by tightening the screws on the main board. However, I still have a problem sometimes when first powering on. I get a hum from the back of the receiver (not through speakers) which coincides with low volume output. After a few minutes hum goes away and volume returns to normal. Then unit works/sounds perfect. Is it a power supply issue? Everything else works perfectly, so I’d hate to damage it. Thoughts? Thanks for your input.
 
I get a hum from the back of the receiver (not through speakers) which coincides with low volume output. After a few minutes hum goes away and volume returns to normal.
Back of the receiver from the power transformer perhaps.
 
has any work been done on the driver boards? the hum pretty much has to be 120hz PS leakage...I would look at any of the local filters on any boards...does it do this REGARDLESS of the input selector at turn on? (I always expect phono to be the loudest)

there are adjustments on the driver boards - have they been done?
 
No work has been done. I played around with it a bit last night. The volume issue is the same regardless of input or speaker channel. I tried both aux. inputs, both tape monitor inputs, phono input and all three speaker channels. Issue was the same in all. I’m getting very light volume, but I did notice (with my ear next to receiver) that the hum comes and goes as I jiggle the volume. I tried deoxing the pots, but the volume pot is tough to get at. Could it just be a bad/dirty pot or is it a sign of something more serious? Thanks again for the help.
 
if the pot has a back end tap for loudness and that is loose it could affect it...any bad solder joints in the power supply near where it feeds the big caps? there are multiple power supply sections..id check them all . make sure the regulated voltages are spot on during this humming. it might require setup of the DVM while it cools then turn it on.

there is a SM on hifi E for free (might even be one here- have not checked).

I have not done an xx1 series in a few year, especially the larger ones, but just ab out every device in there is replaceable and there is a lot of low hanging fruit you want to go after silicon wise if you are up for a restore.
 
Have you placed hands on the main transformer to see if the vibration is coming from there? The chassis bolts could simply be loose.
 
Recleaned the pots today. They’re tough to get at, so I had to do a lot of disassembling to reach them. I was able to get at them and give them a good cleaning. Waited a while, started up unit and still the same problem, low volume. Left it on for a bit and volume kicked back on. When volume kicks in the hum from receiver stops. Turned unit off and then on there is a 2-3 second volume delay (with hum) then a click (relay?) then normal volume. Thanks again for the help!
 
Maybe hum is slow relay kicking on. Could be R11 (10 ohm has increased, or C11 (47uF) has high ESR or open. Or the relay could be bad (not likely but...) (all are on the power supply board with the relay) The fact that the hum goes away when the relay clicks in suggests that the transformer is not the issue. FWIW the protect circuit is on its own winding from the transformer, and no other power supply circuits are.
Far less likely, but small possibility the power switch is arcing, and sound appears to come from the back but isn't. Lots of Kenwood and Pioneer units have this problem, and some describe it as coming from the transformer but it isn't. Best test is to turn the unit on, plug it into a switched outlet strip, and turn it on and off with the strip and see if problems is still there. My 2 cents.
 
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