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Sansui 9090 non DB version excessive current drain

tiomilo

tiomilo

New Member
Hello all mighty gurus of forbidden knowledge, sending greetings from distance and asking a little help, my uncle have his very old Sansui 9090 not working, has blown fuses, trying to fix it just replacing all transistors caps and diodes , resistors too on F2436-1, output transistors too and emitter resistors and main capacitors, now it power on and sounds but the lights go dim and eventually blown the fuses, adjusted BIAS and offset at idle like service manual say, but at very little volume amperage consumption increase exponentially . any advice will be appreciated . thanks a lot.
 
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avionic said:
Double/triple check that you haven't installed a capactor,transistor or diode incorrectly.
Click to expand...

Yes, with that behaviour I'd bet it was one or more 'back to front' capacitors, for example the main PSU ones for the negative supply.
 
The first thing to check in a 9090 is the speaker relay. Some whacky engineer at Sansui thought it would be a good idea to have the relay short the speaker to ground when it turns off. Sometimes the relay contacts get welded together and it shorts the output to ground, drawing lots of current and blowing the outputs. If you can hear sound on both channels, the relay should be ok.
The next thing to check is to look at the output with a scope with no signal to make sure it is not oscillating.
Next look for caps installed backwards. Unfortunately you can't always go by the markings on the pc board, sometimes they are wrong. When replacing caps you have to check the polarity vs the marking before you remove each cap. I just did a 9090dB and I think the polarity markings are ok.
 
updated info; there is a very faint "humm" sound at zero volume almost null, all capacitors are triple cheeked , the protection relay looks fine , infinite impedance without the driver board. btw the sound is good at any volume but at higher levels 50% or more blown the fuses even without speakers attached. it's a very frustrating situation, already unsolder the speakers outputs from the relay board same results.
 
Look at the output with a scope with no signal to see if it's oscillating. Turn the volume up with no input and observe the output for oscillation.
 
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