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Old 23rd March 2013, 07:45 AM   #1
diyAudio Member
Join Date: Feb 2011
Default transistor problem

Hi and thanks for reading this post.

My amplifier has been playing up on me and i noticed a swollen capacitor which i replaced with a new one of the same voltage and capacitance.

When reassembled the amp would not work at all, after a few hours of experimentation i noticed a row of transistors which are clipped onto the metal chassis of the amp, obviously this was done by the manufacturer to keep the transistors cool and i had to unclip these to get the board out.

When the transistors are clipped onto the chassis of the amp so in effect they are all sharing one large heatsink the amp does not work, i gave each transistor its own heatsink and now the amp works fine.

Can anyone tell me what is going on.

Many thanks in advance. John.
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Old 23rd March 2013, 08:16 AM   #2
diyAudio Member
Join Date: Feb 2009
did you remember the electrical insulation between each transistor and sink?
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Old 23rd March 2013, 09:05 AM   #3
AndrewT is offline AndrewT  Scotland
diyAudio Member
Join Date: Jul 2004
Location: Scottish Borders
Originally Posted by goodsguys View Post
........ i noticed a row of transistors which are clipped onto the metal chassis of the amp,..........
This does not sound like a chipamp.
Are you in the correct section of the Forum?
regards Andrew T.
Sent from my desktop computer using a keyboard
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Old 24th March 2013, 07:44 AM   #4
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Join Date: Feb 2011
Hi. Thanks for the replies.

The only thing between the transistors and the chassis was a layer of thermal paste.

When i reassembled the amp i did not put on a new layer of paste, just thought i would power it up for a few seconds to see if the recap had fixed the problem, the power supply made a high pitched whining noise.

So i applied the paste and the whining noise went away but now there is no sound, perhaps the paste was having an insulating effect and separating the transistors from each other and the new paste i am using does not do that.

Can you tell me anything about the electrical insulation between each transistor and sink you mentioned, what is this, is it something i can buy?.

Many thanks. John.
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Old 27th March 2013, 11:35 PM   #5
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Join Date: Apr 2008
Location: Carlisle, England
You need to buy some SIL pads to electrically isolate the transistors from the heat sink.

It could be you blew some transistors by shorting them to the heatsink.
Murton-Pike Systems PCBCAD51 pcb design software.
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