Sansui AU 919 protect

[Lynyrd]

Hello everybody.
Amplifier SANSUI AU 919.
Protect mode,red led flashing.
I want to replace all "black flag"capacitors.
But for begining help me please with protect.
I was tested power supply.
+56v -56v....ok
+55v -55v...ok
+40v -40v.....ok
I desoldered and tested on protect pcb SR601 ...OK.

But the BIAS on both channels is 0mV.
Impossible to adjust.
Where I need control please.

Need help

SM

https://elektrotanya.com/sansui_au-919_sm.pdf/download.html

 

[rayma]

Have you checked the output transistor emitter resistors?
Have you diode checked the output transistors?
Check fuses?

 

[Lynyrd]

I have -3.5v on pin 28 and +2.1v on pin 27 of power amp.
Normally is 0v
Fuses are ok,power transistors are ok

 

[Lynyrd]

It was bad DC offset,after adjust of no protect.

 

[Ian Finch]

This is quite old, like a 40-50 years old model. After probably many years of temperature cycling or even stored away, you could expect many components made from plastics or thin metal conductors to break, malfunction or perhaps they just embrittled or corroded away but you only find this when you try to move or adjust them.

Normally, a technician would routinely replace old components like trimpots to avoid embarrassing failures such as you had there. If you want your amp to have a second or third lifetime, it will be good insurance if you do that too. Measure and match the pin spacings as close as possible and choose good quality trimpots with a suitable power rating.

 

[Lynyrd]

Yes sir