burnt resistors on PPI PCX-1250 amp
Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=77695
Printed Date: May 01, 2024 at 7:48 PM
Topic: burnt resistors on PPI PCX-1250 amp
Posted By: danieljaluise
Subject: burnt resistors on PPI PCX-1250 amp
Date Posted: May 12, 2006 at 6:41 PM
Hi,
I have a precison power pcx-1250 amp, and it just recently stopped working. While connected to the sub, all of a sudden it started to just thump the speaker randomly so I disconnected it and opened it up.
I found two resistors that are completely burnt and I am unable to determine the value of them. They are R101 and R201 and are located right behind the RCA input connectors on the board. If anyone has access to this model amp and could retrieve the resistor values for me, that would be great.
Would replacing the two reistors solve the problem with this amp, or is there something else wrong?
Replies:
Posted By: firstrax
Date Posted: May 12, 2006 at 7:34 PM
A Can you post a pic? My guess is the burnt resistors are a symptom of a larger problem. Resistors are usually not the cause of a problem but rather the victims of the problem. Check the rest of the board for components with signs of heat stress (FETs and transistors). Unless they are FERs (Flame emitting resistors). But due to their relatively short life span few engineers use them anymore.
Posted By: danieljaluise
Date Posted: May 12, 2006 at 9:54 PM
Here are some pictures of the amp. This amp was refurbished and there are some spots (3rd and 4th pictures) where I can tell it was soldered by hand.
The whole board:
Burnt resistors:
Component I believe was repaired previously:
Solder is bridged between two contacts. This is on the the lowpass/hipass switch:
Also, the low pass filter never worked on this amp when I got it, but it drove the speaker fine with an external crossover. Let me know if anymore pictures would help.
Posted By: kirktcashalini
Date Posted: May 12, 2006 at 10:41 PM
Damn you cant even see the rings. Ive had resisters heat up so hot i couldnt touch them but i havnt ever seen anything liek that. wish i could help, sorry, and good luck
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99 Blazer LT. Yellow Top. Big 3. Infinity Kappa Speakers All Around. Jensen CD/DVD flip out. 2 Infinity Kappa Perfect 12DVQs powered by a Alpine PDX600.1 (in one custom box, building a FG box)
Posted By: danieljaluise
Date Posted: May 14, 2006 at 10:50 AM
Update*
Well, PPI technical support was absolutely no help. They told me to take it to a repair shop.
I have been searching the internet looking at pictures of different amp boards to see if I could take a good guess at what the resistances should be. The two resistors that are blown are connected right to the rca input connectors, so I have been looking at that section of different amps to see any similar design.
I did come across these pictures:
ppi pc450
The amp has a similar design and you can see two blue resistors on each set of rca connectors. The color bands indicate they are 10 ohms each.
I'm not sure if I'm ready to throw in some 10 ohm resistors and call it a day, but this seems like a good starting point so far.
Posted By: kirktcashalini
Date Posted: May 14, 2006 at 11:13 AM
doubt it can be of any help though
https://ampguts.realmofexcursion.com/PPI_PCX-1250/------------- 99 Blazer LT. Yellow Top. Big 3. Infinity Kappa Speakers All Around. Jensen CD/DVD flip out. 2 Infinity Kappa Perfect 12DVQs powered by a Alpine PDX600.1 (in one custom box, building a FG box)
Posted By: danieljaluise
Date Posted: May 14, 2006 at 11:48 AM
if only that picture was a little bigger... but actually, I do notice that that the resistors on that board are different from the ones that burned up on mine. Mine aren't blue like in that picture. Maybe that has something to do with why they burned in the first place. Do those blue resistors dissipate heat better?
Posted By: kirktcashalini
Date Posted: May 14, 2006 at 12:57 PM
oooh i see that now, and the base of the resistors you have look odd too, possibly they wwere replaced once... I wish it was easier to read teh code off resistors... If any of you big guysw have a better picture post it maybe we could get the value.
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99 Blazer LT. Yellow Top. Big 3. Infinity Kappa Speakers All Around. Jensen CD/DVD flip out. 2 Infinity Kappa Perfect 12DVQs powered by a Alpine PDX600.1 (in one custom box, building a FG box)
Posted By: oreo lover
Date Posted: May 14, 2006 at 1:15 PM
I looked quickly and found this. You may want to post your pic on this site and see who answers you. https://www.diyaudio.com/forums/showthread/t-50946.html Good luck.
Posted By: danieljaluise
Date Posted: May 14, 2006 at 6:19 PM
Well, I checked that forum out and started a thread there. It seems there is a guy on that forum that used to work for PPI and explained how to fix it. heres the link to that thread:
https://www.diyaudio.com/forums/showthread.php?s=&postid=915929#post915929
I stopped at the radio shack to get the 10ohm 3watt resistors, but they didn't carry them. They only had 10ohm 1watt resistors, so I guess I'll be trying those and hoping for the best.
Posted By: oreo lover
Date Posted: May 14, 2006 at 9:31 PM
Ummm you don't to do that. If the advice given was to source 10ohm - 3 watt resistors then get the correct ones. There is obviously a good reason for it. Failing to replace resistors with identical specifications may result in a much worse outcome. Radio Shack sucks by the way. Go to an electronics store/retailer. There are more common than you might think. Open your Yellow pages and inquire.
Posted By: stevdart
Date Posted: May 14, 2006 at 9:46 PM
You could substitute 10 ohm 5 watt, or 10 watt resistors. Just as long as it dissipates the heat. You could also use three 30 ohm 1 watt resistors bundled in parallel for a 10 ohm 3 watt result.
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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
Posted By: danieljaluise
Date Posted: May 18, 2006 at 4:22 PM
Alright, I was able to get 10ohm 10watt resistors, so hopfully these won't give me any problems. They do look very different from the reular kind of resistors on the amp.
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