Sansui 990 problem

akai_hifi

akai_hifi

New Member
Hi Guys! I have a old Sansui 990 not the DB version. It has been acting up lately and I can't seem to figure out what the problem is. I turn it on and 30-45 seconds later the left channel starts to create static and it increases in volume till Pop! The protection light flashes from Green to Red and back to Green. It will do this and cause the RMS meter to move like crazy. Any ideas what it might be? I am a bit of a noobie when it comes to diagnosing old tech like this. Thanks a lot!

Dave!
 
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Pull the pre/main jumpers and see if it continues. This will tell you if it's the preamp or the amp causing your problem.

You have some DC from somewhere.

Rob
 
Robisme said:
Pull the pre/main jumpers and see if it continues. This will tell you if it's the preamp or the amp causing your problem.

You have some DC from somewhere.

Rob
Click to expand...
Alright Rob. So I Unplugged the Main out and Pre-In connectors and it does the same thing. The protection light doesn't turn red anymore it stays green but the left channel meter is bouncing like crazy. During this process I have no speakers hooked up.
 
UPDATE: So I hooked it up to an audio source. It will play sound through the left channel but the right (which is unaffected) is stronger. With the volume completely down it will still produce fuzz through the left channel. Even with the speakers switched off it will do the same thing.
 
I would start looking at the driver board. Check fuse resistor values. Could be a bad transistor.
Check supply voltages.

Rob
 
You might have a bias issue, due to bad resistors on the main amp board...as well as possibly dirty controls on the pre amp side...she probably needs a good service, if you are capable with a multi meter, pull the main amp board out the slot at the back and start checking resistor values, you will likely find some bad ones, replace them, get some electronic contact cleaner and clean all your switches/ controls on front panel, my self i would recap the amp board whilst out...then fire it up and adjust bias to spec. simple stuff for most here, though if its above your head ask around and there is probably someone loco that could do it for you.
 
and because that board is slot in, you need to clean all contacts in the slot and polish board to suit...crap idea, though makes for an easy service for you.
 
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