Car stereo question -- intermittent audio

[djmcmath]

I'm getting nothing on Google, searching through forums, or asking my tech-savvy friends. I thought I'd check here in PPOT in hopes of a surprisingly obvious piece of information that I've missed.

So here's the data:
- The audio to all speakers intermittently stops, then restarts, as if I've put the stereo into "mute." I can draw no correlation between when the failure happens and any kind of external input -- changing source (bluetooth to FM to AM to CD), unplugging and replugging speakers, opening or closing doors, temperature, or anything else I could think of. I can't make it fail, so I don't understand why it's failing.

- It is an aftermarket head unit, a Blaupunkt 420BT, installed in my 2001 BMW. It worked great for perhaps 6 months before this started.

- The obvious guess is a ground wire, but if it was a bad ground, I'd expect rough audio or overall power issues.

- After a bunch of research, I discovered that some head units have a feature where they shut down all audio output if there's a ground on any speaker wire. Given the age of the car, this seemed liked a reasonable possibility to investigate. So I installed switches in all 8 of the speaker wires and waited for the problem to happen. If this was the issue, I should have been able to isolate it by simply opening the switches to the grounded speaker. No such luck. The problem came and went, regardless of which speakers were connected.

Any thoughts? I'm at a loss here.

Thanks,
Dan

[schamp]

Is there a power amp? If so check the ground on that. Ground should be twice as heavy as power in.

[djmcmath]

Not that I know of. The only amp is the one that's internal to the head unit.

[djmcmath]

Looking at the wiring diagram, there are only two wires labeled "ground" in my setup. One goes to the CD changer, which I don't have, and the other is apparently the main ground for the whole head unit. If that was intermittent, I'd lose power to the whole unit. I don't see anything that looks like a ground which is separate from the main ground for an internal power amp.

[mattdavis11]

Do you have radio controls on the steering wheel?

[djmcmath]

Originally Posted by mattdavis11

Do you have radio controls on the steering wheel?

Yes.

Radio control from the steering wheel is accomplished by translating the button pushes on the steering wheel through a little blue box into the "remote" line into the radio.

What's your idea? What could be wrong, and how would I test for it?

[RANDY P]

if the OE amp has been bypassed the radio is toast. Likely a cold solder joint.

rjp

[djmcmath]

Originally Posted by RANDY P

if the OE amp has been bypassed the radio is toast. Likely a cold solder joint.

rjp

I don't believe there *was* an OE amp. When I put the new head unit in last summer, I did all the right stuff, electrically -- used all the existing wires in the harness, soldered everything cleanly, used heat-shrink tubing to close it all in. If the radio is toast, wouldn't it fail hard, rather than failing intermittently? How would I test (aside from just getting a new one?)

Thanks,
Dan

[RANDY P]

Originally Posted by djmcmath

I don't believe there *was* an OE amp. When I put the new head unit in last summer, I did all the right stuff, electrically -- used all the existing wires in the harness, soldered everything cleanly, used heat-shrink tubing to close it all in. If the radio is toast, wouldn't it fail hard, rather than failing intermittently? How would I test (aside from just getting a new one?)

Thanks,
Dan

Take the radio out, bench it by hooking it to an old car speaker and shake it around.

The fact that all four channels are failing tell me it's in the source itself or the amp power supply.

it probably has an amp in it.....most modern cars do.

[rwest]

Just a theory, maybe it has a thermal shut down if the amp gets too hot. Possibly check the speakers to see if they have too low of an Ohm reading, or too many speakers hooked together making the amp see a low Ohm reading.

[djmcmath]

Update: I pulled the stereo out and had it replaced under warranty -- I had about two weeks left on the warranty period, so I figured it'd be worth the hassle. Same problem. So the stereo itself wasn't the faulted component (most likely).

Totally unrelated to the stereo problem, I've been having intermittent alternator problems. I replaced the battery, because it just wasn't charging well, then I started getting a flickering alternator light, so I replaced the voltage regulator. The flickering alternator light persisted, so I replaced the alternator. The flickering alternator light become more frequent, if anything.

Further investigation showed that the charging terminal under the hood on the right side was heavily corroded. I had thought that was a single-point item, but I discovered that it's actually the connection between the alternator and the battery. So I dismantled that whole connection, cleaned everything up (sandpaper and a file), re-crimped a new connection on, and put it all back together neatly.

And so far so good. The intermittent stereo problem hasn't resurfaced, and the alternator light has stayed out.

In retrospect, it was so obvious that I'm embarrassed to admit I hadn't seen it earlier. #shame Thanks for the ideas, everyone. (But you couldn't have guessed the answer because I omitted a piece of data that I thought wasn't related. My mistake.)

Dan

[GH85Carrera]

Gee I KNEW that was the problem but since you were withholding information I did not tell you.