Stereo receiver cutting randomly in and out

[msintros]

This started happening a few days ago. It is a Sony STR-DE185. Right and left channels cut out independently of one another. At first it seemed to just be the right that was cutting out, now it can be either one or both. The amp doesn't click or go into protection mode, the audio just cuts out either momentarily or until I move things. What I have figured out so far:

1. Doesn't matter what RCA input I am going into in the back, it still does this.
2. Doesn't matter which set of speaker outputs I use (A or B).
3. I don't think it's the cables and it's definitely not the device I'm inputting, as I have tried several.
4. Headphone output is normal. Only speaker wire outputs seem affected.

At first I thought it was just a bad input because when I kinda twisted or otherwise manipulated the RCA cable connector at the right input, it would go away, but now I realize that basically doing anything at all will cause it to either cut out or come back. I have dismantled the thing to clean it and check for bad solder joints and realized that touching or moving half the things on the board will make the output cut in or out erratically.

I thought maybe it was something grounding out to the chassis, so I lifted the entire board out and placed a book under it so that it doesn't contact the chassis in any way. Behavior is the same. Tapping the tops of most of the capacitors or other components on the board will cause it to cut in or out. If the board is in position, even pushing down on it a little bit will cause it to do this. Sometimes even knocking or tapping on the whole thing will cause it to happen. Jiggling either the input or the output speaker cables will sometimes make it happen (sometimes not).

I took the board out and resoldered all the joints for both the input and output jack components with no change. I added solder to any connections that looked even remotely suspect with no change.

The total randomness of the behavior is bewildering to me. If anyone has any bright ideas, I'd be incredibly grateful.

 

[dorke]

When it cuts out ,do you hear a relay clicking?
Try "taping" the board with no input signal,it will make it easier for you to hear the relay click if present.

Have you looked at the flat cables connecting the main board and the display front panel board?
Look for cable tilted or not fully inserted,also inspect connections for corrosion.

 

[KJ6EAD]

When it cuts out ,do you hear a relay clicking?
Try "taping" the board with no input signal,it will make it easier for you to hear the relay click if present.

Have you looked at the flat cables connecting the main board and the display front panel board?
Look for cable tilted or not fully inserted,also inspect connections for corrosion.

Exactly what I was thinking. Sony receivers of a certain era had a lot of problems with speaker relays, either cold solder joints, bad relays or weak power supplies for the coils.

To isolate a mechanical intermittent, try poking the board very gently with a thin non-conductive probe. A bamboo skewer is a good choice.

 

[msintros]

Thanks for the response.

I don't hear any clicking. I've connected and disconnected all the flat cables several times. I've even run it without the cables connected. It obviously won't let me change the volume or use the display, etc. but it still behaves the same. I don't see any corrosion either.

 

[msintros]

Exactly what I was thinking. Sony receivers of a certain era had a lot of problems with speaker relays, either cold solder joints, bad relays or weak power supplies for the coils.

To isolate a mechanical intermittent, try poking the board very gently with a thin non-conductive probe. A bamboo skewer is a good choice.

It does usually do it if I push on the board or often even if I tap on any of the components (doesn't even seem to really matter which ones).

Are the relays the medium-sized rectangular things? I think it says NAIS "Thailand" Spule: 12V on them.

I guess I will have to listen more careful for the clicking you mention. I haven't heard any yet and I have pretty sensitive hearing, but I will give it another listen.

 

[msintros]

I have checked it again with my ear practically right up against the relays and don't hear anything at all. It doesn't seem mechanical to me.

Whatever it is is definitely in whatever part of the circuit is responsible for the speaker outputs. The headphone out behaves normally but both A and B speaker outs are affected.

 

[dorke]

Yes these are the relays.
They sure are electromechanical.

There are 3 "audio" relays in that Sony model(RY781,RY782,RY783).
Ry781 is the earphone one.
Do they all have the same part numnber?

Do you have a digital scope or at least a DMM?
Do you know how to solder/replace components on a PCB?

 

[msintros]

Yeah it looks like they're all the same part number.

I have a Fluke multimeter and I can replace components.

Do you really think it's the relays though, if I'm not hearing a click? Plus it seems weird to me that two relays would suddenly go bad together, but I'm not the expert of course.

 

[msintros]

So I desoldered one of the relays and opened it up. I was curious what it looked like in there, having never opened one before. It looked OK. It was hard to tell if there was stuff on the contacts so I kinda rubbed some notebook paper on it (I read that you don't want to use anything too abrasive because it will score it and decrease the life of the relay). I figured paper would be very slightly rough and might take some gunk off if there was any there.

Anyways, I'm not sure I really had to do this but I just gave it a shot. I then just replaced that relay with new solder and added solder to the other one (which I didn't open). I also added some solder to one of the large filter caps. It looked OK, but maybe a little thin. I don't think that had anything to do with it, but I did it anyways.

At the moment the problem does not seem to be manifesting. I'm gonna give it a while and see what happens. If it doesn't do it at all tomorrow, I think it is probably safe to say that the relays just needed to be resoldered. The existing contacts looked mostly OK to me, not cracked, but there didn't appear to be as much solder on some of the contacts as the other contacts on the board, so maybe the contacts were in fact not great.

We shall see what happens.

 

[Heliman]

If all else fails, when unit starts cutting out, feel components on the board for excessive heat. Then you can try the opposite, when unit starts cutting out try freezing individual components with freeze mist.

 

[shrtrnd]

Everything I've read in the posts here sound like good advice.
Some may consider them dim, but you asked for bright ideas, so here's mine.
I know you checked the cables. The first thing I do, especially if I moved things around, is to RE-recheck all
the speaker connections, outside of the amp.
The second thing I check is the switches on the amp themselves. In particular the speaker switches.
Those switches wear, and can cause intermittent drop-out.
Testing the switch-wear theory is pretty easy. When a speaker drops-out, start exercising the speaker select switches, and then all the other audio output associated switches to see which of them might be causing the
problem.
I vote for serious consideration of the most obvious suspects, before I go tearing into the circuit boards.
Worn switches are a big suspect for me, here.

 

[msintros]

Thanks for the great advice I received here from everyone.

I haven't experienced any more problems a couple days after resoldering the relays, so I guess that was it *knock on wood* It's funny because the joints looked fine but I guess there must have been a crack or something I couldn't see. I would have never known to narrow my attention to those components if it weren't for your help!