Sansui AU101 problem

I started recapping this Sansui AU101 of my father which really needed a revision.

Left channel went perfect, right channel not. Been searching for the problem a few days but still haven't found it. Hopefully anyone can help:

Started recapping the power amp and when trying that stage, resistor R282 fried. Looking around on the net it might be the fault of one of the transistors, but changing those didn't help, still fried the new resistors.

So to test the difference between left (working and recapped) and right (not working) I removed the four transistors TR806, TR808, TR810 and TR812 and the equivalents in the left channel. Plugged the amp and started measuring voltages at different points, both in the left and the right channel. I noticed that the voltage at certain points in the right channel was very low compared to the right. For example between R822 and diode D802 the voltage was 6V and in the left channel 44V (supply voltage = 44V). I suppose that there is a closed circuit somewhere, but I can't find where (tested so much connections, but without any luck).

Anyone an idea to continue my search for the problem?

sansui.jpg
 
just looked high and low and cant find R282
anyway .. i think you have a cap in backwards or you made a short with the soldering ..
 
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I meant 828.

Yeah, I think so to, but I can't find the short circuit, is there an efficient way to find it?

Is it an idea to remove certain capacities power it on and see if the voltage is higher than the 7V?
 
Yes, but i've already tested all transistors and the diode. I really think that there's a short circuit somewhere, I just can't find it.
 
test every resistor in that circuit including vr802 .
with the 27 ohm resistor burning up there are likely more causalities .
 
Local store, but it all works perfectly in the left channel, so don't think it's due to the caps. Tested them as well (not with a cap meter tough, but just testing that it's not short circuited or mega ohms)
 
Local store like Radio Shack?? What brand caps??
Can you take a pix of the top & bottom of your board?
 
If 828 cooked it's a good bet that the transistor below it is shorted....
Curious why didn't the fuse pop ?
It is also possible that when recapping, the bias pot got bumped OR opened up causing excessive current in the circuit.
It's a fairly simple single supply amp...
The way I attack these situations...
Make a print as a mark up of what you test
Look here http://www.audiokarma.org/forums/showthread.php?t=625430&page=13
Post 189...
ALSO build yourself a DBT ( Dim Bulb Tester ) this will keep you from toasting new parts + existing. You might want to google that for a how to build one.. easy & cheap.

Mike
 
Local store like Radio Shack?? What brand caps??
Can you take a pix of the top & bottom of your board?

Got the caps from a local, reputable store in Belgium (Leuven) and Conrad. Not all caps are labeled, some of the brands are classics: Panasonic, Vishay, Nichicon, Yageo. And I keep on referring to left channel: working perfect and sounding great.

I'll take a pic asap.
 
If 828 cooked it's a good bet that the transistor below it is shorted....
Already replaced that one and the old one wasn't even faulty testing the junctions.


Curious why didn't the fuse pop ?
That's one of the reasons why I'm really confused.


It is also possible that when recapping, the bias pot got bumped OR opened up causing excessive current in the circuit.
I'll change that asap. But if I test its' resistance it should be fine.


It's a fairly simple single supply amp...
I know, getting really frustrated :p


ALSO build yourself a DBT ( Dim Bulb Tester ) this will keep you from toasting new parts + existing. You might want to google that for a how to build one.. easy & cheap.
Since classic light bulbs are not available anymore here (Belgium) can I simply use some with LEDs, no problems with all the electronics and stuff?
 
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