Working on a SX-939

Ray122

Member
Hey!

So I'm working on a Pioneer SX939.
Recapped the whole thing, but after I recapped the tuner section I got nothing. My first step when this kinda thing happens is to check and see if the section is getting power. It is, but only about 1.7v instead of the 13 I should be seeing. My next step is to disconnect the power to thee section and see if it's loading the power supply. It seems to be because when disconnected from the tuner section I get the 13V I expected from the power supply section. So then I hooked up my bench supply to the tuner section and gave it 13V and it worked, drawing about .10 amps, which seems okay to me. At this point I think my best bet is to replace all the transistors in the power supply section, but before I do that I figured I'd throw this out there and see if anyone with more experience can confirm or deny my suspicions. Or even just enlighten me a little on trouble shooting the power supply.

Thanks!
Ray
 
Check and deep clean the function selector switch. That switch energyzes the FM and the AM, and was reported bad in several amps. I'd check the voltage reaching the selector and getting out of it. Also, check the AM powers OFF when you set it to FM.

I had to deal with a very hard to find fail in that selector: measuring continuity with a dmm seemed OK, but pressing hard with the probe on the pins caused an internal short.
 
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