Sansui Amp Problem

[edward897]

It is an AU 717. the power on the left channel is scratchy at low volume then it comes on if your turn it way up. Then it goes in and out again. Putting power to it brings the sound back. When it is out you can barely hear the sound. Is this a bad power transistor?

Ed

[Wardsweb]

sounds more like a dirty protection relay.

[edward897]

the protection flashes when you turn it on and it stays on.

Ed

[edward897]

the relay looks shiney and clean.

[RobV]

Bet it's the connected/separated switch. I had the same problem with my AU-819. You can get to it with no more than a phillips, and clean it with contact cleaner. Try flipping the switch a time or two to see if it helps.

[edward897]

where is it?
Ed

[edward897]

ok, found it. should I spray cleaner in it? Or wait until to farts our again and jiggle it?

Thanks,
Ed

[RobV]

On the back panel. To clean it you will need to take off the top cover and probably a dust cover near the back to get to it. To flip the switch, you just need to remove a phillips screw on the back holding a clear plastic piece.

[edward897]

I took the cover thingie off and sprayed into the switch without removing the interior dust cover. It's going well now. Hope this does it. Thanks.

Ed

[RobV]

Spraying contact cleaner at it from the back won't help. If switching it back and forth will does the trick, BEWARE, it is only temporary. I did this enough and now I need a new switch.
To clean it you have to remove the top cover, the dust cover for the rear jacks, so you can get a clean. I found it helpful to also to remove the screws holding the tape and phono RCA jacks so I could safely pull the pre/main board (that the switch is on) up enough to get a good shot at it. Use a towel under it to catch the drippings and flood it it with a stream of c.c. while flipping it to each position.

[edward897]

Will do, thanks again. You're helping me and building your post count at the same time, what a deal.

Ed

[john_w]

If this doesn't do the trick, check out the balance control.

My AU 9500 had the same symptoms. I took it in to have it professionally repaired, and the problem did APPEAR to be the speaker relays. They cleaned the relays, and everything else exposed in the system. Not only did it fix the problem, but the sound quality seemed to improve significantly -- much more clean, and less "grainy". But, they also cleaned every control in the system, so it was impossible to tell what actually did the trick.

This worked for 8 months or so, and I'd have to send it back in. (I'd do it myself, but that's a lot of labor and time to spend on that beast!) I repeated the process several times, then settled on just cranking it up to clear up the signal every once in a while.

Many years (maybe 15?) later, I noticed another complication. The balance control was creating a lot of static when I adjusted it, and I could reproduce the same "cut-out" symptom in the same channel (reduces to very low volume, like you described), just by wiggling the balance control. And, cranking up the volume still fixed it.

This time, having everything cleaned (by a different repair guy) DID NOT fix the problem -- the balance is not noisy anymore, but I can still reproduce the problem by wiggling it horizontally, without turning it. (It still cuts out by itself occasionally, too.)

So...Anyone know where I can get a balance control unit for this amp?

Having it cleaned by a better repair guy might help. I wasn't sure about this guy, since he never reproduced the problem anyhow; he wasn't willing to let it run in his shop long enough to reveal it, and insisted that the problem didn't exist! ("If there was a problem, I would find it.") :mad: He also insisted that the speaker relays could NEVER cause this problem! If anyone knows a really good high-end Sansui repair guy in the Denver area, I'd really appreciate the contact.

[edward897]

Cleaning the connected/separated switch appears to have fixed it. It's been cranking in my garage for several hours over the last two days without the problem occurring. Prior to even cleaning the switch all I had to do was touch it and it cleared right up. I took it apart and sprayed it out just to be safe. All other controls work clean without static.

While I have the top removed should I go ahead and give all the switches a spray of cleaner? The volume control looks like it would have to be removed and disassembled to clean, is that correct?

Ed

[john_w]

Properly cleaning whatever you can while you've got it open can't hurt. But, I'm always a bit leary of spraying cleaner on any controls while they're still in place - especially potentiometer-based ones (like volume, and probably balance). I haven't really looked at Sansui's controls from the inside, but if it looks like you can do so without completely trapping fluid where it could cause a problem, go ahead. Of course, today's highly evaporative cleaners usually don't cause a problem on exposed surfaces; I'd just wonder about getting the stuff trapped where it won't dry up very quickly. Even canned air can blast dust further down into the inner workings, and really mess you up. So, I'd say if nothing else gives you any trouble or noise, you might want to just see how it goes for a while.

Properly cleaning controls often involves desoldering and removing the control unit and perhaps partially disassembling it before cleaning it. If you want to play with it, go for it. It just seems like too much work for routine maintenance to me, unless you're doing it for a living and really have it down to a routine.

BTW: My amp has gone over a decade between cleanings, and only the balance control even hints at any problem.