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Sansui AU-5900 hissing (background noise)

F

franclou

New Member
Hi everyone,

I found a Sansui AU-5900 in an estate sale for 75$ CAN. The receiver wasn't plugged for the last 4 or 5 years and was really dirty (smoker house). I cleaned it good, used Deoxit in all switches, pots and selectors (more then once). After a few minutes of working, the right channel starts to hiss, even with the sound off. The left channel plays flawless. When I lift the SEPARATED switch, the hiss is louder. When I plug the Out in the In of in SEPARATED mode, the hiss is as loud as it was on CONNECTED mode.

I read all the threads concerning this problem, replaced the right 2sa798 transistor (didn't do the left one), replaced the V21212 diodes and the R31,R32,R41,R41 resistors too. The hiss is still there.

I cleaned the relay contact with paper soaked in Deoxit too ... same problem.

Someone told me to let the receiver on a couple of days to help it, but I'm not sure it's a good idea. I like the receiver (found a Tuner

Thanks in advance for your solutions.
 
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Buy some freeze spray, also called circuit coolant spray. Spray just a tiny amount on IC2 on the driver board. If it quiets down or gets worse, IC2 is probably bad. If there is not difference try TR06 on board F-2604.
If IC2 is bad, the original part is no longer available. Don't try ordering one from E-Bay, you will get counterfeit parts. I see that you already replaced it, but if you used a part from any place but BD Enterprises it is counterfeit. You can make a replacement from 2 low noise transistors, but for now try swapping it with the one from the other channel. If the noise goes to the left channel then the part is bad.
 
Thanks, I will try that. I wiggled the relay a couple of minutes ago and the hiss was "disappearing" before coming back. Should I clean it again before swapping ?

Thank you again.
 
All that means is your relay is bad. You can clean it as a temporary fix but it needs to be replaced. The gold coating is worn off the contacts and they will oxidize.
 
I looked at some threads that you answered to (you know your stuff !), I will try to find a replacement relay (seems hard to find with the number of pins I need).

Do I wait to change the relay before going further with my investigation on the background noise ?

Thank you again.
 
Digikey has relays. What is the part number on your relay? You don't have to replace the relay before fixing the problem.
 
The relay number is rabk-2b, I found on one of your threads (I'm becoming a big fan :-) ) that the Omron MY2-02-DC24 would be a replacement for it. Digikey is out of stock, but I found one on the Web at another store. Is it the best one ?

I'm goint to buy the freeze spray now !
 
franclou said:
The relay number is rabk-2b, I found on one of your threads (I'm becoming a big fan :) ) that the Omron MY2-02-DC24 would be a replacement for it. Digikey is out of stock, but I found one on the Web at another store. Is it the best one ?

I'm goint to buy the freeze spray now !
Click to expand...
Yes, that's the one to use. If Digikey is out of stock you can try Mouser. They usually have those relays if Digikey doesn't.
 
I did what you told me to do and you were right, the left 2sa798 was bad. I put my old right one in and everything is fine now. Sounds a amazing ! I will change the relay though and would like to know how to make my own 2sa798 using low transistors.

Thank you, thank you and thank you !
 
The 2SA798 is just 2 matched low noise transistors with the emitters tied together. Here is how it is wired:
871363-DI1.gif

So you just buy a few low noise PNP transistors (I can get you a part number later), match them for Beta and wire them as shown. You tie the emitters together and put one of the leads where the emitter went in the original. Try to keep the transistor cases as close together as possible so they stay at the same temperature. You can heat shrink them together.
 
If it's not too much to asked, I would like to have the parts number when you have the chance. Kind of a newbie here :-)

Thank you so much !
 
Dr Audio will correct me if Im wrong but KSA992 x 2 works a treat. If you have a meter or tester that shows you transistor hFE you need to get a couple as close as possible.

I just did this fix on a Pioneer M22 and a lot of problems went away like magic.
 
Hey .....
I didn't want to open another thread as I have similar noise problems with a AU 4900,but I think it's not a relay problem.
It's like white noise on both channels,already audible on 9 o'clock volume,gets louder on higher volume
and stays the same on all inputs (phono louder) and stays same if i set balance left or right.
Until now I changed all capacitors and fuse resistors and cleaned all switches and potentiometers.
I have already here replacement for all critical transistors.
Recommended from http://www.audiokarma.org/forums/index.php?threads/once-more-sansui-transistor-substitutions.583009/

Should I change them?

Thanks for help

Gregor
 
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