Does this amp look to be hard to fix?

mazeroth · 26th August 2006, 04:46 AM

I just received this amplifier that I purchased off this thread:

http://www.polkaudio.com/forums/showthread.php?t=42900

It came it near mint condition and 4 of the 5 channels are working. In the one picture (you need to scroll down the thread a little) you can see on the left where the resistor looks a little burnt. I was curious how hard it would be to fix something like this, and if someone like myself could do it? I have a friend with a $150 Weller soldering iron that has a ton of experience soldering active crossovers that could do the work for me. I haven't asked him for help yet, and was wanting to get a little bit of information here first.

Lastly, do you think I did ok for $160 shipped?

Thanks!

clem_o · 26th August 2006, 07:36 AM

If the channel isn't producing any output, suspect the output transistors. It's easy enough to fix - IF you know which parts to replace. Finding out which ones (I am pretty sure it isn't only the resistor in question) is the one that takes skill, time and effort. I'd guess that your crossover expert friend would probably be able to do it...

Cheers

TomWaits · 26th August 2006, 02:00 PM

That is a five channel amp and it seems four of the channels work perfectly fine. I may be wrong but theoretically it is an easy fix and you won't necessarily need a manual as you should be able to read and measure the component values from the good channels.

A few hours to assess and a few hours to fix.

Cheers,

Shawn.

djQUAN · 26th August 2006, 02:08 PM

it looks more like the soot originated from the small mustard colored capacitor similar to the one in the middle of the pic.......

Leolabs · 26th August 2006, 03:59 PM

The most important thing is know how to use a multimeter to measure the componets,esp semiconductors.

Nrik · 30th August 2006, 09:55 AM

You definitely need to replace the emitterresistors, and the outputtransistors in both positive and negative section.
You might also need to replace the drivertransistors.

It is not enough just to replace those components that looks burned, because you can probably not see which ones of the transistors that are gone.

So if you have interest in electronics, and know how to solder, you can try to replace all the mentioned items carefully, and make sure that the new transistors have sufficient thermal contact with the heat sink.

If it allready sounds too scary then dont do a half attempt - send it to a dealer for proper service.

YES the amplifier is definitly worth it!!!

SpittinLLama · 30th August 2006, 05:12 PM

I'm with DjQUAN, I think what looks like a monolithic ceramic cap (snubber cap) probably popped as well as the emitter resistors are also burnee out. The output transistors might still be functional but with burned out Re's then you would not have a connection to the load.

Best to have someone who knows something and check the transistors first to see if they are dead then go from there replacing what is blown.

-SL

26th August 2006, 04:46 AM	#1
mazeroth diyAudio Member Join Date: Jul 2004 Location: Columbus, OH	Does this amp look to be hard to fix? I just received this amplifier that I purchased off this thread: http://www.polkaudio.com/forums/showthread.php?t=42900 It came it near mint condition and 4 of the 5 channels are working. In the one picture (you need to scroll down the thread a little) you can see on the left where the resistor looks a little burnt. I was curious how hard it would be to fix something like this, and if someone like myself could do it? I have a friend with a $150 Weller soldering iron that has a ton of experience soldering active crossovers that could do the work for me. I haven't asked him for help yet, and was wanting to get a little bit of information here first. Lastly, do you think I did ok for $160 shipped? Thanks!

26th August 2006, 02:00 PM	#3
TomWaits diyAudio Member Join Date: Aug 2005	Not too difficult That is a five channel amp and it seems four of the channels work perfectly fine. I may be wrong but theoretically it is an easy fix and you won't necessarily need a manual as you should be able to read and measure the component values from the good channels. A few hours to assess and a few hours to fix. Cheers, Shawn.

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26th August 2006, 07:36 AM	#2
clem_o diyAudio Member Join Date: Jun 2005 Location: Manila	If the channel isn't producing any output, suspect the output transistors. It's easy enough to fix - IF you know which parts to replace. Finding out which ones (I am pretty sure it isn't only the resistor in question) is the one that takes skill, time and effort. I'd guess that your crossover expert friend would probably be able to do it... Cheers

26th August 2006, 02:08 PM	#4
djQUAN diyAudio Member Join Date: May 2004 Location: manila	it looks more like the soot originated from the small mustard colored capacitor similar to the one in the middle of the pic.......

26th August 2006, 03:59 PM	#5
Leolabs diyAudio Member Join Date: Dec 2004 Location: Bukit Mertajam	The most important thing is know how to use a multimeter to measure the componets,esp semiconductors.

30th August 2006, 09:55 AM	#6
Nrik diyAudio Member Join Date: Feb 2005 Location: Copenhagen	You definitely need to replace the emitterresistors, and the outputtransistors in both positive and negative section. You might also need to replace the drivertransistors. It is not enough just to replace those components that looks burned, because you can probably not see which ones of the transistors that are gone. So if you have interest in electronics, and know how to solder, you can try to replace all the mentioned items carefully, and make sure that the new transistors have sufficient thermal contact with the heat sink. If it allready sounds too scary then dont do a half attempt - send it to a dealer for proper service. YES the amplifier is definitly worth it!!!

30th August 2006, 05:12 PM	#7
SpittinLLama diyAudio Member Join Date: Apr 2005 Location: In the Wild, Wild West	I'm with DjQUAN, I think what looks like a monolithic ceramic cap (snubber cap) probably popped as well as the emitter resistors are also burnee out. The output transistors might still be functional but with burned out Re's then you would not have a connection to the load. Best to have someone who knows something and check the transistors first to see if they are dead then go from there replacing what is blown. -SL

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