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Pioneer Receiver Repair

S

Shadly

New Member
Hello, I've got a vintage Pioneer I was hoping to repair. Hopefully you all can talk me through it. It's a model sx-737. I can tune it and i can hear the stations if I put my ear to it, but I can't hear anything coming from any of the channels (i.e. phono or speakers). Is there a pre amp or something that could be out? I think it's weird that I can hear it really low coming from inside the case. Any ideas?
 
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Moving to Pioneer forum. Does not appear to be a tuner issue with the receiver.
 
If you don't hear the speaker relay click, one of the output stages is probably blown.
 
Do you have the correct set of speakers turned on? There is a pair of buttons for speakers A and B. Need to make sure you have the corresponding speakers hooked up and selected on the front panel. Make sure the tape monitor switches are not engaged as well.

Also could just need a cleaning of the controls with deoxit/faderlube.
 
Yeah, I don't think it's something easy like that. I just took the cover off and checked a few things. With the headphones plugged in in the front, it does start working for like 30 seconds if you look at it funny. But then it cuts out again. I tried wriggling components to see if i could find a short, but nothing compelling.

Are the back channels the four components located at the center of the case? I can hear (faintly) the radio coming from them. Does this rule anything out or narrow it down?
 
Shadly said:
Yeah, I don't think it's something easy like that. I just took the cover off and checked a few things. With the headphones plugged in in the front, it does start working for like 30 seconds if you look at it funny. But then it cuts out again. I tried wriggling components to see if i could find a short, but nothing compelling.

Are the back channels the four components located at the center of the case? I can hear (faintly) the radio coming from them. Does this rule anything out or narrow it down?
Click to expand...

Sorry, I mean output stages (not back channels).
 
I think you're referring to the output transistors? They'll be mounted to a big black heatsink with fins. Dime-sized round metal cases with wings. This is not unheard of, to be able to hear audio from an amp even with no speakers.

I'd still want to clean the controls before I start pulling output transistors, etc.
 
Ok, I'll do that first. Are there particular controls I should focus on given the symptoms?

Also, just looking down the line, the board with the four fuses has some big capacities on it that have some rust on their housings. Is that a sign they are shot or dying?
 
shadly, given that you unit turns on, lights up, doesn't smoke and the speaker relay engages the very first step is to give the switches and potentiometers a cleaning with Deoxit D5. I'd suggest you use the search bar on your sign in page and search for - switch cleaning, pot cleaning, potentiometer cleaning - these results will guide you on how to do this properly. I've never been inside a SX-727 and am not sure how easy or difficult gaining access to the switches and pot is and maybe someone who has experience can chime in.

I wouldn't undertake any other repairs until I did this cleaning. Good luck
 
The fact that you can hear the audio coming from the output transistors and the relay clicks means the preamp and power amp are ok and audio is getting to the output transistors. The only things left are the speaker relay and the speaker switch. Try this: connect your headphones and tap on the speaker relay (it's the plastic box about 1" by 1 1/2") with a non metallic object, like a Bic pen. If you hear some audio through the headphones when you tap the relay, the relay is bad and must be replaced. You need to desolder it and solder in a new one. Cleaning the contacts will only work for a short time because the gold plating has worn off and the base metal will start oxidizing rapidly and you will be back with no sound.
 
Ok, so I spoke too soon about the relay. It clicks intermittently on and off. When it's on, the receiver works fine. When it's off, i hear music from the output transistors, but not from the speakers obviously. All the knobs and switches work well.

I'm not convinced that wriggling or knocking the relay gets it to come on. Is there another component that can be faulting intermittently, causing the relay to activate/deactivate? Or is this likely the relay itself falling.
 
lots to check and different ways about going through it .. power supply voltages are always a good start as if that is wrong then nothing else will play along nicely .
you first need the service manual .the meter of course . tape to cover your test probes so only tiny tip showing .this saves blowing stuff by shorting things out .
also read old threads on similar faults with your unit .
no rushing .take your time and ask questions .
 
Do you suggest I pull the relay and hook it up to a 24VDC source first to see if it shorts on its own? Wouldn't that be the easiest thing to do first?
 
no it is not a concern right now .. get yourself prepared and await instructions on how to proceed .. you cannot rush these things .even the best techs on the planet cannot rush things without making mistakes .
 
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