Bizarre (?) Electronics Problem...

[Peter B.]

For reasons I need not go into here, I own two (2) identical stereo receivers. They are both about 15 years old.

I've been using one regularly, while the other was kept as a spare... and has been unplugged for at least the last year or two.

Recently, the receiver in use stopped 'making noise'. It had worked fine the previous day, but the next, when turned on, there was no sound at all from the speakers... on any input. The unit turns on, goes through the protection circuit dance, the display shows the input source, but no sound... unless the volume is turned ALL the way up and the source can be heard... very, very faintly.

The spare receiver had been tested prior to being put upstairs... and it worked fine... no problem.

Rather than make any effort to diagnose the receiver (recently) in use, I brought the spare downstairs, thinking to swap it into place for the other. I just happened to bring a speaker and a length of zip cord downstairs to check function of the spare before putting it into use.

To my surprise, it now seems to be suffering from the identical problem... turns on, lights up, but no sound.

I opened up the spare receiver, checked the power amp output fuses (with an ohm meter) and they were fine. I checked the fuse that (I think) provides power to both amp stages... and it was fine. The main power fuse is fine.

That's about as much as my diagnostic skills allow.

Somehow it seems hugely unlikely that the two receivers would fail - with the same problem - within the same week... especially when the spare was known to be good and hadn't seen use for some time.

To my knowledge, the units have no internal battery that might power a 'calendar' or cumulative use logic chip that might trigger a planned obsolescence function... and only my paranoia suggests that there might be such a function in the design.

But this has got me completely stumped.

Any ideas?

Thanks.

Peter B.

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[Dix]

Do you have another set of speakers, and clean wiring to make a new connection?

 

[billb3]

hearing aid battery


if you checked the fuses out of the circuit , then you need to check the wires for opens or shorts , especially if the amp has safeties for the amp that shut down if they don't se the right load.

 

[oldspark]

Head phones work? I would try another set of speakers also as mentioned above.

 

[Peter B.]

Checked speaker wires for continuity... checked speaker for ohm load... normal.

Speakers won't 'blow out' without overload or severe clipping, and would likely go gradually and audibly.

Note again - two receivers, two failures with identical symptoms, in the space of a week.

Peter B.

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[homebrewz]

Yeah.. try headphones. It is very strange that both receivers would do the same thing and with a completely different speaker. It sounds like the signal is not getting to the speakers. Could be a bad ground somewhere on the board, solder joint, broken wire going to the audio output to the speaker jacks, etc. Perhaps an overly simplistic explanation, but I have an older receiver on which I've sometimes hit the wrong button sending the output to another pair of speakers which aren't hooked up.

 

[oldspark]

Checked speaker wires for continuity... checked speaker for ohm load... normal.

Speakers won't 'blow out' without overload or severe clipping, and would likely go gradually and audibly.

Note again - two receivers, two failures with identical symptoms, in the space of a week.

Peter B.

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Wire to the speakers, did you check the wires for ohms?

 

[blades]

Sure sounds like you hit a mute button or perhaps some other signal diverting/ selecting switch for the audio output considering that that you hooked a different speaker up and got the same problem on a second reciever or did you mean that when connected to the primary speakers the problem appeared? If so I would look very carefully at the speaker terminal connections at the speakers and the unit particularly if the terminals are studs of some type as it sounds like a short.

 

[Peter B.]

I wish it were something as simple (and 'Doh!') as the speaker select switch, mute, or similar.

Yes, the resistance of the speaker wire was checked, and it's fine. Good stout lamp cord with tinned ends.

Though I have no plausible explanation for it myself, I just can't #$%! believe the two receivers would 'go down' in the same fashion, within such a short time span... wired to different speakers.

Again, one receiver used regularly for over a year - failed from one day to the next - in the manner described. The second receiver, idle for the same year (and more) - failed with the exact same symptoms - using different speakers.

Gremlins, I sez... and nothing but.

Peter B.

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[oldspark]

Do the head phones work?

 

[Peter B.]

Don't have headphones.

If you're thinking it's the power amp, other devices (equalizer, etc.) aren't receiving input source from the tape monitor.

It seems like there's no output from the pre-amp... or as if the source signal never reaches the pre-amp.

Try Again ???

Peter B.

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[oldspark]

Take the receivers upstairs and see if they work there maybe?

 

[Peter B.]

Take the receivers upstairs and see if they work there maybe?

oldspark:

That's about the only thing I haven't tried that seems to hold any promise. I'll let you know.

To all, thanks for trying. I'll post back if I can figure this out... but I wouldn't hold your breath.

For what it's worth, over the years I flatter myself that I've developed enough logical skill to at least eliminate consideration of the obvious.

But at present, I remain stumped.

Peter B.

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[WhitePine]

Have you had any close lightning strikes lately? Lightning can take out sensitive components just by inducing currents in their wire leads. The strike does not have to come in on the power, telephone, cable, or over the air antenna wiring, or any metallic path at all. It can destroy some equipment solely by induction. Which brings up the next question, were these two receivers both hooked to anything while in their separate locations?

 

[Peter B.]

Have you had any close lightning strikes lately? Lightning can take out sensitive components just by inducing currents in their wire leads. The strike does not have to come in on the power, telephone, cable, or over the air antenna wiring, or any metallic path at all. It can destroy some equipment solely by induction. Which brings up the next question, were these two receivers both hooked to anything while in their separate locations?

No close strikes... nothing worrisome. I tend to think of my computer before other components in those cases and don't recall unplugging.

The 'spare' receiver (exhibiting the same problems as the primary) has been nowhere near a power outlet for over a year.

--

For what it's worth, I've dealt with other problems with both receivers through the years... and have learned from one to apply remedies to the other.

This 'matched pair' of symptoms is different than any in my experience...

PB

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[WhitePine]

High quality receivers tend to have very sensitive components in their front ends. It doesn't take much to knock them out. Computers are much more "hardened" against surges than receivers.

Any chance of a strike when nobody was around?

When I asked if they were hooked to anything, I meant anything, not just power. Were the receivers hook to any kind of antenna or cable system?

 

[Peter B.]

High quality receivers tend to have very sensitive components in their front ends. It doesn't take much to knock them out. Computers are much more "hardened" against surges than receivers.

Any chance of a strike when nobody was around?

When I asked if they were hooked to anything, I meant anything, not just power. Were the receivers hook to any kind of antenna or cable system?

WhitePine:

Thanks for your diligence...

The receivers in question are 'budget quality' Optimus (Radio Shack) offerings. I have two because I thought they had a very clean sound for an entry level unit.

The receiver 'in use' has been hooked up to nothing more than an indoor antenna ('rabbit ears') for most of two years... no cable.

The spare, 'upstairs' receiver was plugged into (absolutely) nothing for most of two years... but was (without question) a working unit when shelved.

I'm still here...

Peter B.

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[WhitePine]

Here are all the possibilities I can think of in the order I think most likely.


1. An aging component that failed, most likely an electrolytic capacitor. It would be unusual for two caps in different pieces of equipment to fail about the same time, but not impossible. However, the spare unit may have degraded to the point of failure sometime in the past two years, which would not be all that unusual.

2. The aforementioned nearby lightning strike.

3. An embedded battery that ran out in both units.

4. A software error that is date sensitive. That would require the receivers to be able to get current date/time information. I think that information may be carried on a sub carrier on some FM stations, but I could be wrong.

5. Completely unrelated random failures with identical apparent symptoms.

 

[Later]

1. Kids overdriving the speakers?
2. Speaker fuses blown?
3. Shorted stranded wire connection at speaker or amp.

Aging electrolytic capacitors usually produce a 60 Hz hum in the speakers.

Disconnect the speaker wires at the amp and very briefly touch them to a penlight battery - listen for a clicking at the speaker.

 

[WhitePine]

Aging electrolytic capacitors usually produce a 60 Hz hum in the speakers.

Electrolytic caps aren't just used in power supplies.

 

[Peter B.]

I'm leaving this for the moment and hoping food or sleep will provide a fresh view.

Thanks for your help and I'll report back if there's any progress.

Peter B.

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[Later]

Aging electrolytic capacitors usually produce a 60 Hz hum in the speakers.

Electrolytic caps aren't just used in power supplies.

Quite right, they replaced the ceramic and paper ones from the good old days.

 

[Peter B.]

I'm more than a little embarassed to report that an oversight (on my part) in the realm of 'idiotic' has now been addressed and the spare receiver is working again.

So the compelling 'mystery' I reported last night amounted to nought.

One receiver only is down... and that no longer seems such a surprise. The cause is not yet determined, but I'll give it a shot in days to come, and if I find out, I'll report back.

Thanks to all for your help... and I'm sorry to disappoint... it seemed like a good story on the surface.

My apologies.

Peter B.

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[billb3]

progress is progress

sometimes it helps to start over but even then it can be hard to ignore biases of thought

hope you end up with a spare again

 

[WhitePine]

So, you aren't going to let us in on the actual oversight. Your choice, of course. ;-)

No pressure. :lol: