Sansui Seven FM Stereo Light Stays ON

[jackson]

Howdy- I just acquired a nice Sansui Seven- seems fully operational so far, but the FM Stereo light stays on all the time. Relay? Transistor? Any guidance is appreciated- Thanks

 

[Robisme]

I would check TR411 and 412. Looks like 411 turns on 412 which gives the lamp a ground potential.

See if TR412 is on without 411 turning it on.

Rob

 

[jackson]

Thanks will try!

 

[jackson]

Update after locating the components you mentioned and further testing it never seems to go into stereo the FM stereo light is always on but when tuning it always stays in mono should I look further or just test those components first? Thanks

 

[kevzep]

If this is the case, then there could be two different problems.
How are you checking for stereo?
The STEREO light staying is usually a shorted transistor which switches the lamp on, no STEREO would indicate a MPX problem which may be cured with an alignment.
But it could also be component failure....

I would check the switching circuit for the STEREO lamp as per Rob's instructions and go from there.

 

[KeithD]

There's usually a variable resistor (VR) that sets the threshold for when the stereo light comes on. If set too low, the stereo light will stay on all the time. SM shows it is VR402 on the multiplex board.

 

[kevzep]

There's usually a variable resistor (VR) that sets the threshold for when the stereo light comes on. If set too low, the stereo light will stay on all the time. SM shows it is VR402 on the multiplex board.

Yeah, auto-detector threshold.
I think the OP said the unit is mono even with the stereo light on, but that could be the MPX separation adjustment, was pretty common for that to be user adjustable on many units of this era, usually on the back panel somewhere.