Radio problems...I may have FUBAR'd the thing

[Sean H]

A quick rundown of the components before I begin:
Blaupunkt Nevada headunit
Blaupunkt A08 changer
Infinity Kappa 255a amplifier

The problem: I was looking to install an antenna adapter to the head unit (turned out to be the wrong part, which makes this doubly frustrating). The constant power lead turned out to be chaffed and upon placing the head unit back into the dash it arc'd, most likely to the adpater plate for the head unit. Since then, I'm getting tremendous alternator noise through the system, along with headlight noise as well (with the car not running I only get a few "pops" during changeovers of songs).
The system ran clean (i.e. no noise) before this. What potential problems am I looking at? Melted wiring? Damaged head unit or amp? Any help would be appreciated, as I've already suffered a roundtrip to the keys with no music (I had to talk to my girlfriend the whole time!) and I'm not looking forward to much more road time minus my tunes.

[danzee]

From the history and symptoms you report, it's likely that some fiiltering or the alternator was damaged. My opinion is the odds favor a damaged alternator or filter, not the radio. Quickest path forward might be to get the alternator checked first.
My thinking:
The alternator whine is normally filtered out by an EMI filter(s) or just feedthrough capacitors. Some radios have similiar internal filtering on their DC inputs. Another strong possibility is that you damaged a rectifier in the alternator, and that is causing high ripple which will produce the noise. Turning the headlights on increases the alternator load and would result in more noise with a bad rectifier or filter. Finally, there's a slim chance that you damaged a ground connection that's part of the filter bypass path (unlikely). My wild guess is that there's a bad rectifier in the alternator.

I don't have a schematic of the car, so it's hard to tell your where to look.
You could try the radio in another car, if possible, and eliminate it by substitution. If the radio seems okay there, have the alternator checked out at a shop. Otherwise you will need to start looking for the noise tracing the circuit from the alternator to the radio and amp. You will need some electrical expertise and equipment to do that.

[Sean H]

Thanks for the help. I failed to mention that the headlight noise is present when the car is on, but not running (battery power only) as well. I'm sorry my original post wasn't too clear on this part. Does this point more towards damage in the filter in the head unit (assuming it has one)?
In terms of the curcuit from the alternator to the radio and amp it's essentially the same as a stock car. The amplifier is powered from the battery and has a remote on from the radio. The radio uses the stock power wires. I'm not sure if this info is useful at all, but I thought I'd throw it in there.

[Javier]

the "constant power wire" was the engine running? Did you blow the F41 fuse? Replaced it? Checked it?

If engine wasn't running, no damaged could be caused to alternator, but you may have blown an incoming filter at the head unit, look for an electrolytic capacitor, 25 Vdc and about 100uF (or similar, we are just testing), and connect it from "constant power wire" to ground (careful it is polarized). If noise is reduced (or removed), you probably damaged the internal filter, just open the HU and look for the first capacitor connected from the "constant power input" to ground, it is the must probable cause of the problem. Also look for burnt portions of the printed circuit leads between this capacitor and said input.

Javier

[Sean H]

No, the car was off at the time. All the fuses check out OK. I'll look into the innards of the HU when I next get a chance.
Thanks again for your help.
This once again proves the knowledge ont his board is greater than all others. I posted the same looking for answers on the Car Audio section of another, major BMW board and didn't get so much as one reply.

[Javier]

sense of partnership.

Javier

[Rory]

No, the car was off at the time. All the fuses check out OK. I'll look into the innards of the HU when I next get a chance.
Thanks again for your help.
This once again proves the knowledge ont his board is greater than all others. I posted the same looking for answers on the Car Audio section of another, major BMW board and didn't get so much as one reply.
Why not hire a copmetent engineer from that fine University down the street from you. You know, the place where you should have gone for undergrad? I'll bet McCoy can fix it and if not just bring it up here and i'll do it for you....I do have a 5 lb sledge ;)