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Old 18th August 2008, 11:32 PM   #1
diyAudio Member
Join Date: Jun 2005
Location: UK
Default KSA-50S ruined?

Hi all!

I just sold my FPB-200 in favour of keeping just my beloved KSA-50S.

Only problem was that the output relay on the right channel of the 50S needed fixing or replacing. Today I disassembled the KSA-50S, cleaning the output relay of the right channel. I also removed some dust, and then reassembled the thing.

It fired up as normal, and sounded fantastic.
HOWEVER, the LEDs that show current bias level kept being lit (both red and blue LEDs) to show that full bias was on (on both channels), and after some time the amp was extremely hot. Too hot to keep switched on, and the thermally controlled bias shut down didn't kick in either.

I don't even know where to begin fault searching. Did I blow up something on the logic board behind the front panel, perhaps? Is there a way to disconnect things from the front panel to force lower bias level.. (Assuming the logic board at the front controls this functionality.)

It's just a daunting task to try to fix this without risking to create more problems.

Is there an expert on the KSA-50S out there who might like to help me against compensation?

I'm also looking for a replacement KSA-50S to tide me over, and as a fallback solution should things keep going pear shaped..

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Old 19th August 2008, 07:17 AM   #2
diyAudio Member
Join Date: Jun 2005
Location: UK
I guess a start would be to try to find the complete schematics for the KSA-50S, including the logic board. I tried googling it, but no result. Anyone has any ideas?

I'm gutted.
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Old 19th August 2008, 01:55 PM   #3
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Join Date: Sep 2004
Location: MN
I would carefully go back and retrace your steps. Its easy to have left something disconnected, or for a wire to come off unknowingly. or something to have gone back on backwards. Go slow, take your time and look it over good and see if you see anything out of the ordinary. 9 times out of 10 its something simple.
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Old 19th August 2008, 04:48 PM   #4
diyAudio Member
Join Date: Jun 2005
Location: UK
Thanks for the advice!
Unfortunately I'm pretty sure nothing like that happened. However, I did some stupid things, on the assumption that the circuits were stone cold (no power). I'll go into the details if anyone wants them!
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