Sansui 5000A Right Channel out Left Channel Distortion

[Chris J]

I am new to vintage audio so patience please.

I have a 5000A I want to bring back to life. I ran a line out from the Tape A REC just to see if the radio and phono amp work and everything seems fine when I run it through a separate pre amp/amp.

When I try using any of the three speaker outputs (a, b, or c) via the integrated amp the right channel is out but makes loud pops when I switch the high/low filter and the left channel makes awful noise when I turn it up or down. There is audio from the left - just very low.

I cleaned the pots and switches with a bunch of deoxit. They are very smooth now but that did not help the problem.

I replaced the 4 big capacitors C003 - C006 because the wires looked like they had been hot at one time and because three were discolored and one was an obvious earlier replacement. That did not help but it did not seem to hurt either.

I have the service manual, a digital multimeter, willingness, and lots of time. How do I begin to isolate the issue(s)?

 

[blhagstrom]

Start researching the known problem with the 5000A.
They were flawed in the original design and actually recalled because of a potential fire hazard.

Popping on the filter switch would indicate tired capacitors on that circuit and can probably be left off to the side for now.

"Awful noise" is not really descriptive enough to give us any clues.
Popping, crackling, screeching, hissing, humming, etc... help a little.

Repairing electronics is all about chasing voltages and signals (digital multi meter, o-scope). Testing transistors and diodes, then resisters. Looking for bad solder connections.

Look up dim bulb tester and build one of those.
Look up testing transistors and learn how to do that.

Do you have a good soldering station and skill to do good soldering and unsoldering?
A good work space with good light? It may be a long process and be torn apart a while.

The 5000A is really not a great place to learn electronics. It could be a real trial by fire experience.
I have one in a pile that I don't even really want to see how good/bad it is. It came with a bunch of other stuff that indicates someone was hacking.

 

[Chris J]

Start researching the known problem with the 5000A.
They were flawed in the original design and actually recalled because of a potential fire hazard.

Popping on the filter switch would indicate tired capacitors on that circuit and can probably be left off to the side for now.

"Awful noise" is not really descriptive enough to give us any clues.
Popping, crackling, screeching, hissing, humming, etc... help a little.

Repairing electronics is all about chasing voltages and signals (digital multi meter, o-scope). Testing transistors and diodes, then resisters. Looking for bad solder connections.

Look up dim bulb tester and build one of those.
Look up testing transistors and learn how to do that.

Do you have a good soldering station and skill to do good soldering and unsoldering?
A good work space with good light? It may be a long process and be torn apart a while.

The 5000A is really not a great place to learn electronics. It could be a real trial by fire experience.
I have one in a pile that I don't even really want to see how good/bad it is. It came with a bunch of other stuff that indicates someone was hacking.

I have seen some posts about the 5000A having issues but not fire. The fuses seem to be holding but I will keep an eye on it and do some more research.

So what I hear you saying is leave the high and low filter switched off and I can come back to that later if I get it working.

Awful noise = popping, crackling, screeching, hissing, humming, etc... It seems to do all of these when I play with the volume. I can hear music playing low and kind of in the background and when I turn it up to hear the music better it pops and cracks and scratches and all manner of unpleasing sounds and the music doesn't really get any louder. I don't expect anyone to diagnose the issue by this description. I just thought it is important to note that there is sound (music) coming from the left channel but something is seriously wrong.

I have a digital multi meter and I am ready to start chasing voltages. I'm just not sure where to start or how I can quickly isolate one component from another. For example - there is no pre out or main in on this unit so I cannot really check to see if the preamp works when I run it through a working amp or if the main amp works when I run a working preamp through it. If I could do that and eliminate the preamp then I would focus my efforts on the main amp or vice versa.

Note: I may be missing something very basic but I don't see voltages listed in the service manual. On my pioneer sx-780 the diagrams in the service manual show voltages.

I have a bulb tester somewhere - I am assuming I can easily use that to find a bad transistor without knowing voltages or anything specific. I will look it up.
I can solder and unsolder well enough but there never seems to be enough light..

 

[blhagstrom]

There was concern about them being a fire hazard that Sansui did a recall. Years and years ago.

I haven't looked at the service manual for these yet. I may need to, I have one in a pile in the pile in the garage.

Since you have one channel working, you can to side-to-side checking for voltage. The trouble with that is, one bad transistor or other parts can throw a lot of things off so it gets hard to pin point.

Years ago when I was very noob to repair, I had one of these that had a bad balance pot. It made the channel all sorts of nasty. Just tossing that out there because that was a lot of the problem with mine. I had other issues that I had to deal with later.

You may need to study up on testing transistors. There is a sticky thread in here (AK) about that.

http://audiokarma.org/forums/index.php?threads/bipolar-junction-transistor-testing-basics.43186/

I haven't spent a lot of time inside the 5000 since I learned up electronics. Perhaps someone who has will step up to help more.
May need to be patient. End of summer, holiday, etc...

 

[Chris J]

This is all helpful. I will focus on the left channel first since it kind-of works. Now that you mentioned it the equalizer amp or tone control would be a logical place to start on the left – beginning with the potentiometers and working back towards the driver amp.

I got down in there really good with the Deoxit using the straw and cranked those babies back and forth about 100 times. I have confidence it’s not a dirty pot. But as pointed out one of the pots could be defective or have a bad solder joint. I will inspect it this evening and report back.

One other thing - one of the heat fins on the back is loose - on the right side where the output transistors are mounted. Someone was in here messing with this thing before I got it so no telling. If I get the left working I guess on the right side I would start at the opposite end and work forward? First thing first though.

...And thanks for the link above I will read through that today.

 

[Chris J]

I brought the unit up from the basement to start troubleshooting and now both left and right do not make sound - except when I switch the low filter button I get a pop out of the left speaker. I did a pretty thorough visual inspection and poked around a bit looking for loose or broken solder joints but nothing obvious is jumping out at me. I thought with one side half working I might be able to isolate and track down the issue. Now with both sides completely silent I am less sure.

 

[two.dogs]

Take some pictures and post them. Include some shots of the 2 amplifier boards near the big caps at the back.