Bass Amp Failure

BOCHIN · 1st April 2005, 05:00 PM

A friend of mine gave me his Bass Amplifier so that I could repair it. He said that it stopped working when he accidentally placed the wrong kind of speaker to the system (he has 8 ohms outputs and connected 4 ohms speakers, pretty lame!).

I checked all the output transistors and one of them was dead, changed it and had to repair the board because it had lots of broken paths. After doing this y plugged it in and sparks flashed from the board, I thought it was a short circuit somewhere, checked it and nothing was apparently wrong, after this I plugged it in again and smoke come from one of the output resistors.

The funny thing is that the resistor that burned was from the PNP transistors side, and the trasistor that was dead was a NPN...
Please help!
Another thing, smoke came out of the resistor... is it dead?

The amplifier is a Trace Elliot of 150 W, I have the schematic, any help will be apreciated.

Giaime · 1st April 2005, 07:25 PM

So... let's start with the easy things. Yes, smoking resistors need to be replaced since they're unable to dissipate their nominal value of power.

The not-so-easy thing: well in a transistor amp you can't just replace the output transistor you found dead. Most of the time a dead tranny (and remember to say if open or shorted - it is important) takes away with him driver trannies, resistors, diodes, pots, etc... so check everything! I really mean EVERYTHING! Capacitors (even power supply ones), the power rectifier, output trannies, ALL trannies on the board (ALL!), diodes (especially if you find ones placed on the heatsink), resistors that have burnt down (sometimes they burn without smoke - especially the metal film ones)...

Posting the schematics also will help.

Good luck!

anatech · 2nd April 2005, 01:31 AM

Hi Giaime,
I guess when you burn you learn! Sage advice sir.

-Chris

Giaime · 2nd April 2005, 11:46 AM

Quote:

Originally posted by anatech
Hi Giaime,
I guess when you burn you learn! Sage advice sir.

-Chris

Eheh... I've learnt from you Chris!

At least I'm doing some tedious work for you (if helping unexperienced people is tedious... and I don't think so...)

Bye!

anatech · 2nd April 2005, 06:48 PM

The best way to learn is to teach! It helps you understand the subject better.

-Chris

BOCHIN · 2nd April 2005, 07:51 PM

The tranny I found dead was short circuited and several paths in the board (specially the ones from ground) where burned out. I will start checkig the entire board, please continue to check on me here, your helpis truly appreciated. I will post the schematic in a few days, thanks

Giaime · 3rd April 2005, 12:59 PM

Ah, burned tracks are a bad sign. They're difficult to repair and they points to a major short that probably fried something also in the power supply. Strange you didn't burn the fuse...

Good Luck! And keep posting...

1st April 2005, 05:00 PM	#1
BOCHIN diyAudio Member Join Date: Mar 2005 Location: en el tolon	Bass Amp Failure A friend of mine gave me his Bass Amplifier so that I could repair it. He said that it stopped working when he accidentally placed the wrong kind of speaker to the system (he has 8 ohms outputs and connected 4 ohms speakers, pretty lame!). I checked all the output transistors and one of them was dead, changed it and had to repair the board because it had lots of broken paths. After doing this y plugged it in and sparks flashed from the board, I thought it was a short circuit somewhere, checked it and nothing was apparently wrong, after this I plugged it in again and smoke come from one of the output resistors. The funny thing is that the resistor that burned was from the PNP transistors side, and the trasistor that was dead was a NPN... Please help! Another thing, smoke came out of the resistor... is it dead? The amplifier is a Trace Elliot of 150 W, I have the schematic, any help will be apreciated.

2nd April 2005, 07:51 PM	#6
BOCHIN diyAudio Member Join Date: Mar 2005 Location: en el tolon	More info The tranny I found dead was short circuited and several paths in the board (specially the ones from ground) where burned out. I will start checkig the entire board, please continue to check on me here, your helpis truly appreciated. I will post the schematic in a few days, thanks

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1st April 2005, 07:25 PM	#2
Giaime diyAudio Member Join Date: Oct 2004	So... let's start with the easy things. Yes, smoking resistors need to be replaced since they're unable to dissipate their nominal value of power. The not-so-easy thing: well in a transistor amp you can't just replace the output transistor you found dead. Most of the time a dead tranny (and remember to say if open or shorted - it is important) takes away with him driver trannies, resistors, diodes, pots, etc... so check everything! I really mean EVERYTHING! Capacitors (even power supply ones), the power rectifier, output trannies, ALL trannies on the board (ALL!), diodes (especially if you find ones placed on the heatsink), resistors that have burnt down (sometimes they burn without smoke - especially the metal film ones)... Posting the schematics also will help. Good luck!

2nd April 2005, 01:31 AM	#3
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Giaime, I guess when you burn you learn! Sage advice sir. -Chris

2nd April 2005, 06:48 PM	#5
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	The best way to learn is to teach! It helps you understand the subject better. -Chris

3rd April 2005, 12:59 PM	#7
Giaime diyAudio Member Join Date: Oct 2004	Ah, burned tracks are a bad sign. They're difficult to repair and they points to a major short that probably fried something also in the power supply. Strange you didn't burn the fuse... Good Luck! And keep posting...

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