KR 3200 I let out a lot of magic smoke

S

srinath

Super Member
OK I shorted the output and "poofed" it. My first, so sad. It was so nice sounding.

It seems to have burnt a pre driver transistor and a few diodes (the ones just ahead of the 2 big caps on the power amp board.

I'll look up the schematic and post what it may be.

But it let out lots and lots of smoke for just those 2-3 components.

Cool.
Srinath.
 
Schematic

Schematic of power amp here.
Thanks.
Srinath.
 

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I have a burnt Q9 - a673, burnt r55 and r53 - .47 ohm, 2 watt 10% resistors, D1 some sort of double diode, r37 - 100k, r49 - I am not sure if that's its number. I'll look again. Yes R49 - 33 ohm 1/2 watt.

When these are removed, I get sound in left channel but right channel (the channel I removed these from) has a weird hum.

Thanks.
Srinath.
 
Last edited:
Great

That is the bias circuit ? Is it bad to run the amp without those components ?
I was going to swap those parts in from the left channel and test it ?
Is that bad ? should I wait to get the right parts before powering it up again ?

I didn't see any issues form the 1 min I powered it up ... it worked when I shut it down.

Thanks.
Srinath.
 
Great, thanks

OK good to know, thanks so much.

In place of that diode can I use a pair of 1N4148's in series ?

Then I just buy some a673's and resistors etc etc and swap em ?

Thanks.
Srinath.
 
do some research on the mv-13 see what others have used . i looked for a data sheet and it was saying it was a zener diode . another said stabistor . others saying general purpose rectifier .
best bet is check voltage drop over the good one in the other channel first
 
The circuit shows it as a double diode with a 1.3v drop. That's the 13 in mv-13.

I also saw that one saying stabistor, and this thread - http://www.audiokarma.org/forums/showthread.php?t=361380 has suggestion to put 2 1N4148 in series. I'll see if I can pull the other channel one.

I might as well get the transistor swapped and tried out too, cos the diode and transistor are very tangled up on the board. Its easier to pull them both at the same time.

Cool.
Srinath.
 
I put these components from the other channel - the left was un burnt from before.
Now the right channel humm and its not dependent on volume, and the volume is very very low, 3/4 volume just to be barely audible.

Could I have burnt something else - the complimentary to the A673 ?

Thanks.
Srinath.
 
there is only 6 transistors to the whole channel .. i think its best to renew the lot .
there might be more toasted resistors . they don't always look burnt .
 
The bad channel 1213 tested with a lower Vf than the other, like 118 Vf vs 145 Vf.
Hope that is the fix.
I am hoping its not all the transistors and hope no more resistors. There is no room on that board and the trace keeps comming off when I remove components. And that's not even on the burnt part.
If it doesn't fix it - the 1213 swap, the thing is getting tossed into my veritable parts pile.
Cool.
Srinath.
 
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