Left Channel Static in 4ch modes

[orionspants]

Hello

I'm very much a novice to this whole vintage audio game but have plunged in head first and picked up several systems so far to listen to and see which sound I like the best.

I got a Sansui QRX-3500 just over a week ago, I managed to get the guy down to half his asking since when I had him hook up all 4 speakers it had channels dropping out.

Popped it open and it was immediately apparent that 2 speaker fuses were blown (they were 3.15A instead of 3A) got 2 new ones and it sounds great although the rear right channel needs to be kicked in by way of isolating it on balance and upping the volume (this doesn't need to be done if it was recently used though and warmed up). BTW the 22WRMS seem quite under rated compared with my Pioneer QX-8000a.

So after enjoying the sound on it for almost a week, static/crackling (whatever you want to call it, like radio fuzz) started to occur in the left front channel. Switched speakers and it is def. the FR-LT. Looked again at the fuses and shifted them around, no change, sprayed some Nu-trol Control cleaner (for the 2nd time) around the vital selectors and knobs inside, still nothing. There is no popping sound (unless the channel is isolated and volume tweaked), just static, that increases/decreases with volume control. The static is also not constant, it crackles, seems to come and go at certain intervals.

I switched it over to 2 channel and it's gone (also fine on 4ch discrete). So now I'm quite worried that it's something to do with the matrix/decoder as it only occurs when it's in use. And unfortunately unlike the Pioneer the Sansui does not deliver 2ch sound to all 4 speakers just the front. The inside of this unit shows almost no signs of wear and is in excellent condition. One thing I noticed after opening it up again to check for anything visibly wrong was that when using the Nu-trol all-in-one is that the lubricant does not dissipate, even in open areas, it also built up in places and I wonder if at a certain point too much of this stuff can interfere all at with the current or board?

You may not be able to see it in the photo but the clear wire coverings at these contact points have collected the lube and are full, it totally surrounds the wire. I've since left it open to allow air to move freely and hope some of the excess will dissipate and squeezed most of the deposits out of the ends of the wires, but it made no difference.

It still sounds awesome in 2ch on the front speakers but that's obviously not why I bought a quad.

Hoping the quad folks will know better than on regular audio forums so if anyone could tell me where to start looking for solutions for the static (and dropping channel) I'd really appreciate it!

 

[DuncanS]

Welcome to QQ. Looks a nice piece of kit. The Sansui must be 40 years old (?). Are there any internal connectors between parts of the unit that could have oxidised and give bad/no connections? My gut feeling its due to failures of Electrolytic Capacitors, they age and then fail. It occurs especially after units haven't been used for a long time, or stored in a shed/garage, then powered up. When power is applied they're Ok then they start to leak current, if its in bias circuitry you get amps working then fading out as everything warms up. The capacitors can go short circuit as well. As you can hear noise coming from you 'dead' channel, you're possibly right the fault could be before the power amp. But it could be in an early amplification stage of the power amp, and you're hearing the noise amplified. I tried hunting for a schematic for the unit on line, but no luck. To fault find you really need a signal source and an oscilloscope. Is there a friendly and knowledgeable repair shop near by? as that's probably your best bet.

 

[orionspants]

Thanks for the reply.

After you mentioned Electrolytic Capacitors I took another look on the top and bottom of chassis and underneath I can see some soldering which seems out of place, however knowing nothing about these electronics at all and nothing about how it looked originally I'm not sure. But the 2 uninsulated wires don't look standard at all to me.

How difficult is replacing these components? From looking at the solder points it seems straightforward but I'm sure there are some elements to it that may be tricky? i.e. stored voltage? Looking that the image there is that hard candy-like amber resin on the points and this resin can be found all over some of the other boards as well. Is this something that should be cleaned off?

The only issue I have with going to to a repair shop is knowing nothing about repairs, so the guy could tell me it's a 2 hour job and I wouldn't know any better. I've maxed my budget already picking up a Pioneer QX-8001a and a little Sony SRS 2ch so I need to chose one of the quads (or both and ditch the Sony). The QX tuner is in need of an adjustment (another fix I wouldn't know how to price) and also has an odd issue of all speakers dropping off at random times but seems not to happen when fully warmed up. One stereo will go in the living room as my main audio and the other in basement workshop. I only entered the vintage world just weeks ago and dove in head first, now I have my hands full it seems!

 

[Doug G.]

Those wires are OK. They are what's called "braid" and are just acting as jumpers to ground for those capacitors. No need for insulation around them as they are at ground potential and there are no other uninsulated wires around them anyway.

The "resin" on solder joints is just hardened flux and won't hurt anything. It's just left over from production.

Your earlier observations do, in fact, point to the decoding circuits as the problem area since, when you remove them from the chain (regualar two channel stereo or 4 channel discrete), the crackling disappears. The output circuits are OK. Otherwise you would get the trouble regardless of in which mode the receiver is.

With the unit on and listening to it, take a wood stick and push around on the decoder board to see if you can make the problem come and go. if so, it is most likely a solder connection gone bad.

Doug

 

[orionspants]

Thanks for answering my queries, just sleuthing, looking for anything that seems out of place.

I tried nudging pretty much everything with a small stick to check for any variance in the static but no discernible changes in sound. The only things that 'seem' to effect the static are using the low/high filter buttons, volume and loudness etc. All of which have been thoroughly cleaned.

I also took off the board's metal protectors and cleaned them as well, still nothing. Guess it will have to go to a shop and I'll see if it can be fixed for less than $50 if not I'll have to put it back on the market as I don't think this model is worth pouring too much money into but probably perfect for someone who knows how to do a little work.

At least I have my QX-8001A to listen to however it's also exhibiting strange problems, like cutting/fading in and out entirely for over an hour. I think this relates to it warming up but what would cause this kind of issue?

Seems quads are a harsh mistress and I'm 0/2 thus far. I haven't given up on them yet but am watching the classified daily for other gear.

 

[Doug G.]

Please remember that, if you want quad, you don't have to go the quad receiver route. You can always use separates. I have always done this and like the versatility.The only advantage quad receivers had/have is that all the stuff was/is in one package but that's a minor thing, really (OK, and most of them are absolutely beautiful, so you have that ).

All you need to do is have stand alone decoders/demodulators and enough regular 2 channel stuff to drive both front and back speakers. For instance, my system has a Sony SQ/QS decoder, Panasonic and Technics CD-4 demodulators with associated turntables and Heathkit amplifiers (one of which has a tuner in it so it's the receiver version) to drive the four Advent stacks.

Although I have the technical knowledge to repair all this stuff, it's a lot easier to sub in another amplifier or whatever if one of the pieces develops a problem rather than have to deal with a complete receiver disrupting everything.

Doug

 

[Ralpharoni]

Glad to see this thread. I hope you get it sorted out. Sweet looking unit! I am watching because I have a similar problem with a Technics SA 6800x and have started a thread which is waiting for admin approval. Perhaps you will see useful info there. The nudging with a stick is a good idea and I will try that. I agree with Duncan's advice on Electrolytic Capacitors and plan to recap the board as soon as I can be sire which one it is that has the problem. I'll let you know if I find anything out. If you can solder you can recap. Just be super careful with polarity when you put them back and use just a touch of rosin when soldering and de-soldering. The solder will flow faster and have less chance of overheating the trace on the board and lifting it. I use copper de-soldering braid to remove the old excess solder before soldering the new cap in. Many prefer a solder sucker but the braid is cheap and easy. Good luck! I'll keep an eye on the thread.
Ralph

 

[leevitalone1]

caps are like batteries, they hold current for short bursts of power when needed. They get old dry up and need to be replaced. It's the biggest issue with older amps. If I was you, I would do a little at a time, and soon enough, you will possess a gem! ( diamond in rough now)The old Sansui's are great quad amps.