really strange PPI amp malfunction

Hi, I have a PPI PCX-1250 amp. This summer as I was driving it all of a sudden started thumping the sub out of control without any reference to the actual sound signal.   I shut it down within 20 seconds for fear of damaging the sub. It was just pushing the sub all the way in and out, buzzing, it would stand the cone out of the basket for a few seconds....all kind of random stuff.   So when I opened it up, There were two resistors that were burnt right near the rca inputs.   I tracked down a guy that claimed he used to work for PPI and he told me to replace them with 10ohm 3watt resistors. I did this and hooked it back up. It worked for about a minute and then did the same thing as before so I disconnected it again.   I took out those resistors and replaced them again with 100ohm resistors this time, same thing.... There does not appear to be any other problem on the board (visable) The explanation I got from the guy for as why the resistors burned in the first place was that I had a bad ground and the amp was sourcing the ground through the RCA cables..    Any ideas guys on what I should try next??

Send the amp to a reputable repair shop in your area... It doesn't have to be a PPI repair center, any repair tech worth his salt should be able to repair a basic amplifier. Whether it is "sourcing it's ground through the RCA's", I wouldn't be able to tell you absolutely, but I doubt that's very likely; if that were the case, you would be burning circuit board traces in your head unit. Have it repaired properly. This by-guess-and-by-golly repair method you are using is only going to cause you grief, and cost you money. Eventually, you are likely to try something that might actually cause the amp to become unrepairable (which repeated soldering and unsoldering processes WILL do - that's VERY not good for circuit boards), and then you are looking at buying a new amp, rather than just getting this one repaird correctly the first time.It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

^^ Second that. There's a reason you're cooking those resistors, I suspect they're the symptom & not the problem. You need some qualified help on this one.

I would love to take it to a repair shop, but they are way to expensive. I only paid $150 for the amp, and I'm sure it would cost that much to get it fixed. I spent some more time with it today, it seems to only 'freak out' when the volume reaches a certain level. It plays fine softly, but as soon as you turn it up it starts goin crazy. The thing that really bugs me is that this problem just started out of no where, and previously I had been running the amp with no problems for almost a year

i am an idiot wrote: The resistors are 10 ohm 3 watt           put them back in and if you have an ohm meter you need to unhook your patch cord from the amp and check resistance from the shield of your RCA jacks on the amp to the non bridged speaker wires    this should be about 10 ohms. If this is not the case let me know. With your patch cords still unplugged you need to check from the shield of the cable to ground more than likely is going to show well above 100 ohms if it does you have a burnt trace inside of your radio.    let me know the results and I can tell you how to fix it.

I soldered in the 10 ohm resistors again, and checked the resistance. With one test lead on the rca shield and the other on the (-) speaker output terminal, it read 10 ohms. I was not getting any reading at all when I put one test lead on the rca cable shield in my car and the other lead to the ground in my car. I tried this with the stereo both off and on and got no reading both times.

by the way, here is a link to my original thread from a while back, it has a couple pictures. Here

Did some more testing: Subwoofer RCA outputs With one test lead on the RCA ground shield and the other test lead at a grounding point, I got no reading. Rear RCA Ouputs with one test lead on the rca ground shield and one test lead at a ground point, it read 500 ohms. then when I switched the red and black test leads, I got 1K ohms. This leads me to believe that the radio is at fault here, not the amps. Now for the best part. The Head Unit is an AVIC-n1, and when I first got it I thought there was too much noise on the rca outputs so i sent it to pioneer under warranty, and they sent it back to me claiming there was nothing wrong. wtf!! So, now that I have narrowed the problem down to being in the head unit, is this something I'd be able to investigate myself, or should I forget it?

wow im gonna have to get some pictures on here soon.... I opened up the avic-n1 head unit and that thing is craaazy complex. Is there anything specific I should be looking for as far as the "burnt trace"?? I am trying to work my way back from the rca outputs on the board but so far nothing jumps out at me...

i am gonna kick my own ass for not doing a simple search on the forum before I decided to disassemble the entire n1.   Apparently grounding the rca shield is a temporary fix and a good way to tell for sure if you have a burnt trace in the radio. I went over each board in the n1 3 times and didn't see anything wrong. Granted most of the traces on the boards are thinner than a strand of hair, I think that I'm going to put it back together and just try ground the rca's on the outside. Hopefully this is my next to last post, I'll let you guys know if that fixes it.