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Sansui 800 Channel Imbalance

W

W.T. Holt

Active Member
Working on a really nice unit right now, Sansui 800, cosmetically very clean, all bulbs light up, everything seems to be great EXCEPT the left channel is very quiet and lacking bass compared to the right.

I have THOROUGHLY cleaned all the knobs and switches on the face plate, checked for poor solder joints and blown fuses and poked around on the left side amp board with my multimeter. No issue has yet to present itself. The problem persists despite my efforts.

What else can I check? Seems like bad volume pots are a very common problem with these 800's, resulting in sound though the speakers with the knob all the way down (an issue my unit also demonstrates)... Could a bad pot cause the opposite problem (not enough volume) on one channel as well? I doubt it but perhaps...

Seeing as the problem is only in the left channel I'm guessing there is a component in the left side signal path gone bad, but I'm not sure which this would be. Are there any usual suspects? Where is the best place to start the hunt for bad parts?

Any and all advice is wanted and welcome!
 
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"ANYTHING" almost is possible but no, imo just a pot causing low output on one channel isn't usually the most common problem. Output at low setting is an entirely different thing, more of a manufacturing problem of its time. Clean the controls as a starter! It's usually a bad component(s) causing the problem and the only way is to first, isolate what section the problem is in. Use different inputs to eliminate that it's in the main amp or another section.
 
I thought about it AFTER I logged off.......... it's been quite a while since I worked on one of these but in reflection they use caps for output coupling. They are the biggest problem with output level and with blown outputs. It'd probably be a good thing to just replace all four of them and be done with it. If you're not sure which caps I'm talking about it's the four lined up next to each other at the very back center inside the unit.

Ron
 
Excellent, thanks for the tip. I haven't worked on cap coupled designs before... its all a bit foreign to me inside this Sansui. Will be replacing those caps soon though!
 
I'm back again... Replaced the output coupling caps. NO difference in sound, the left channel still sounds as weak as ever.

The problem definitely seems to be in the main amp/output section seeing as the problem occurs no matter which input is being used. I have cleaned all the switches and knobs on this thing many times.

I have tested the output transistors - no shorts to be found... I suppose its time to start looking for bad components on the amp board?

ARGHHH, starting to pull my hair out over this one.
 
I saw your post in the other 800 thread, mine has same problem with volume on one channel. When volume knob is set at zero I can still hear sound from one channel. There is an older thread about this problem, I remember someone reporting there that when he replaced the volume pot the problem was gone.
 
Interesting. I have been keeping the volume knob in the back of my mind as a less probable cause, but maybe its time to dig in deeper. Do you remember if, in the older thread, replacing the volume pot fixed the volume discrepancy between the left and right channels, or just took care of the signal coming through the speakers with the volume all the way down. Seems like those are two separate issues to me, but maybe they are both tied to a faulty volume pot...
 
Well look at this way it was a good thing to replace the caps anyhow. The only thing you can do is to track the signal back and find the discrepancy. If you're going to look at replacing things like volume post and the like it'll get hectic in a hurry. Measure and check them out first, pots don't usually add resistance uniformly, more like erratically or open non linear places in the travel.
 
I have a Nikko cap coupled receiver Sta_501la that had the exact problem, turned out it was a bad cap just before the speaker output on the eq board...a tiny little guy
 
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