Sansui au 4900 .Realy in protection mode

luck79

New Member
Hello guys
Today I have a problem with this Sansui 4900.
Here Dc Offset
between
R 37,39 it's ok +/-3,8 volt
R 40 0 volts
R 38 16,4 volts :(



thank you in advance
Luciano
 
Check the main PSU voltages +/-35V approximately.

Take out all the output transistors and measure them using the 'six way test' - or use a transistor tester.

Measure all 4 of the emitter resistors 0.33Ω

That should get you started - good luck.
 
If the PSU voltages are good and output transistors checkout fine your next best shot for good DC offset are the IC pair at output stage (2SA798) that are known to be failure prone.
These are replaced by the modified KSA992 transistor pair per channel.
 
If the PSU voltages are good and output transistors checkout fine your next best shot for good DC offset are the IC pair at output stage (2SA798) that are known to be failure prone.
These are replaced by the modified KSA992 transistor pair per channel.
Hello Mr . Nick

transistor are ok
I have to test ic01.02 (2sa798)
diode 601,603 are ko

I changed them,but does not work.

thank you for helping me
 
transistor MJ15025 ko
I hope to find the spare part,
and no other damage....
this fault on this transistor determines the non-functioning of the relay?
 
transistor MJ15025 ko
I hope to find the spare part,
and no other damage....
this fault on this transistor determines the non-functioning of the relay?

You are better off to build a "Dim bulb tester" (DBT) to power on your AU4900 next time. Power on through DBT will protect your other components on the output stage.
https://antiqueradio.org/dimbulb.htm

There might be other driver transistors blown as well.

MJ15025 is probably contributing to the 0V problem at R40.
Find and replace that output transistor pair on the bad channel and next power on through DBT.
 
Remember to use regular incandescent light bulb. No halogen or eco. I have used regular 60W with my DBT with good results.
It's likely that other driver transistors are bad as well when output transistors fail.
 
Thanks for your suggestions.
I had already devised this alternative to variac.
Good news the amplifier is fine in tape mode sounds stereo ,but it only sounds on the left ( stereo mode), while in mono it plays in both channels, of course I checked the attacks rcf problem is with aux, tuner, phono
I verified bias is ok
 
I checked all the transistors of the F 2555 board and all the Aux, tuner, phono, tape monitor, mode selectors.
But the problem remains. It is heard only from the left and in stereo only in tape mode.

someone has some ideas?
 
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