Sansui 9090 Indicator Light Question

[Ray122]

Hey everyone!

I'm working on a 9090, and I'm about to upgrade all the indicator lamps to LEDs, however I'm experiencing a little bit of a weird and likely stupid problem where the Aux and Phono indicator lamps aren't receiving voltage when engaged. I checked the lamps first and they're not burnt out, and I've cleaned the the rotary switches very thoroughly. The FM, Dolby FM and AM lights all work, and according to the schematic they all receive voltage from the same place as the Aux and Phono lights. So is there something I'm missing that the schematic isn't telling me that would explain why this would be the case?

Thanks!

 

[Sansuiman]

Are you certain in cleaning the rotary switch the fixed contact points for the two affected function lamps weren't bent or misshapen? If they aren't gapped right where they meet the rotary contact, they won't "make" the circuit. Fairly easy to mess these up when cleaning the switch wafers if a very light touch isn't used.

For that matter, if you removed the switch from the board and broke it down, was it resoldered well on reinstallation? I don't aim to insult anyones abilities, but sometimes the obvious simple explanations are easily overlooked.

 

[Ray122]

Are you certain in cleaning the rotary switch the fixed contact points for the two affected function lamps weren't bent or misshapen? If they aren't gapped right where they meet the rotary contact, they won't "make" the circuit. Fairly easy to mess these up when cleaning the switch wafers if a very light touch isn't used.

For that matter, if you removed the switch from the board and broke it down, was it resoldered well on reinstallation? I don't aim to insult anyones abilities, but sometimes the obvious simple explanations are easily overlooked.

No worries! Wouldn't be the first time I was caught with my pants down. I just used a generous amount of contact cleaner and exercised the switch well, so all the points should be okay, but I'll definitely check the gaps though, hadn't thought of that!

Thanks!

 

[Sansuiman]

Ok. I've actually used a toothbrush to aid in cleaning these before, and if using that approach some care is needed. Really, a buzz box (ultrasonic cleaner) and some good contact cleaner is a worthwhile investment if doing this kind of work with any regularity.

In any case, this is a fairly simple circuit, non-recrified 7 volt tap right off thetransformer, and only the switch and some minimal wiring between that and the lamps so not many potential points of failure.