Trouble-shooting help.

[White'88LSC]

How can I Tell if my amp or my head unit is bad?
My front speakers (both) crackle on not to loud peaks, but it's not the voice-coil scraping, speaker-shot, kinda sound. It's the dying amp section or perhaps a resistive ground or conector?
Anyway, with the fadder all the way to the back, I can just make use of the system at low level without the crackle, as the fronts are turned almost all the way off.
So first off, how do I tell if the amp or the head unit is doing it?
Any good tricks out there folks?

Tnx in advance,
smile.gif

[SQ_LSC]

Sounds like dirty contacts in the Head Unit. The best way to troubleshoot this is to swap units out with known good units. Here's something to try though. Operate all the radio controls rapidly through there full range of movement. This sometimes will make an improvement for a short period of time and could tell you if it is indeed the HU.

[White'88LSC]

The plot thickens! Latest find is that with
the engine off, and ign sw in either ACC or ON, the unit sounds much better with the fronts coming to life, and nary a crackle.
but fire it up and the fronts (when the system comes back up)continue to play for about 1-2 seconds then go into heavy crackle, but the rears still play as before.
If I turn it back down, the fronts stop the crackle, but no music from them, just low level music from the rears.
Now I realize that with the engine running the voltage is up a couple to the typical 14v or so vs. the 12.6 open cell voltage in the ACC or ON position (engine off).
could bad connections still be the culprit?
BTW I know the sound of alternator whine or spark plug interfearence. this sounds like the amp is operating way out of range or something.
Ideas on where else to look, don't have a working head unit to replace it with.

thanks again. :rolleyes:

[SQ_LSC]

Now it's starting to sound like clipping. Have you made any changes in the electrical system in the engine compartment that could cause a higher voltage than before like an alternator/regulator swap? Different sized pulleys? What is the voltage with the car running? After an extended period of running, can the volume be turned up? If this is the case, then bad connections/weak battery could be the cause.

[White'88LSC]

I was just going to get into that! The previous owner (PO) had indeed replaced the alt. and the had to replace the regulator twice!. Seems it was over-charging the Battery causing it to swell and leak.
the last regulator seems to have fixed the problem (but perhaps brought up a new one),
as the voltage is 14.2 and I don't think that's high enough to cause a problem.
The irony is that it works better at the lower voltage.
I also discoed the reg. and ran the engine and the front channels came back again???
My next plan is to change out the reg. with the one in my parts car and see....and re-check the running voltage.
BTW, what's max voltage in the system, 14.5?

thanks for keeping with it! :rolleyes:

[SQ_LSC]

now it's making sense. The regulator still seems to be set too high as indicated by the stereo symptoms. Try and get it under 14v. The higher voltage will continue to cause wear and tear on the 12v electrics throughout the vehicle if left unchecked.

[White'88LSC]

SQ, I still value ur inputs, but I have to disagree with u on "overvoltage". The factory manual allows 2.5 volts over the "base" voltage as measured at the battery. My battery starts at 12.6 volts, either static or running without the regulator . With a known to be good FOMOCO regulator swapped in the run voltage at idle still sits at 14.2 rising to 14.6 @2000rpm no load and doesn't drop below 13.5 with eveything turned on, so it passes the undervoltage test as well!
with an open cell voltage of 12.6 and 2.5 additional volts allowed in float charge that would allow 15.1 volts and still be ok according to Ford???? And I'm running 14.2,
so I should be ok. I was hoping to save the original factory system (which is the luxury system with the big amp), but I don't know which way to turn. My parts car has developed a loud poping sound thruout the system. So I don't trust the amp or head unit to swap with, but I guess it's coming down to a lot more labor to find nothing, or start with a new cd system, and forget the original thinking.

thanks again for listening :confused:

[SQ_LSC]

I agree with your tests. I usually use a reference of 2 volts above base voltage which comes in at 14 assuming 12 volts base. The symptoms you were pointing out pointed towards an over voltage problem which the car had. I'm wondering if it did damage to the radio,....If you can think of anything else, nomatter how insignificant, throw it out. I'm gonna ponder this a day or 2 and see if I come up with anything. You should do some voltage tests at the radio and amp if possible on both the power and a/c audio signals. Don't worry about the speaker leads though. A band aid might be to add resistance into that circuit as a last resort. If you do take some readings, take them like you'd do the alternator under no load and loaded conditions. Maybe something will raise a flag.

[White'88LSC]

Thanks again SQ, for the thoughts. I do think my charging system is ok, but you reminded me of what the seller (po) said,
"My son used a cassette adapter to play cds through it and he must have blown the front speakers. The rears still work though."
Now I hadn't even checked it out yet when he mentioned it so I assumed he was right! The more I think of it, the more I suspect the amp. At the levels his son was probably playing it, He probably fried it, more likely than the head unit.
Next chance I get, I'm gonna chance swapping my unknow amp into this situation and see what happens.....stay tuned ;)

[White'88LSC]

SQ et-al, I'VE GOT TUNES!!!!
It turned out to be the amp after all, and not such a hard thing to swap either, with the exception of getting my OLD body in and out of that coffin of a trunk smile.gif
Ponder no more my friend, and thanks again! :D :D :cool: