Pioneer SX-939 phono issue

Hey All, first problem post of new member here.

Pioneer SX-939, pawn shop find, works great on FM and AUX for hours, no problems. After a few minutes on phono, it starts popping and cracking, channels coming in and out.

I have taken off the cover and slightly disassembled to clean switches, pots, etc with deoxit products before I ever used it. I have not yet done a full recap (& transistors) yet, one day this will be done.

I've read elsewhere on here regarding a pioneer sx-850 that the transistors in the phono amp stage need to get replaced. I have pdf copies of the manual and service manual from another site.

Would my issue be in the Control amplifier assembly?

The manual has listed a tuner assembly, power amp ass., control amp ass., equalizer amp ass., and the protection circuit.

Thanks for any ideas and help!

No expert but it sounds like noisy transistors in the phono/equalizer amp board, specifically 2SA725/6's. Replace with KSA992 and it should quiet it down. Had the same issue with my sx 838.

Thank you, I thought it may be the transistors. I have to research this a little more before I order all the parts and redo it.

I'll give an update in a couple weeks on my progress.

it's alive!

thank you buttahman! my pionner sx-939 phono input is working like a charm after replacing the four 2sa725/726s on the equalizer board. I went ahead and replaced a total of ten 2sa725/726 transistors with fairchild ksa992fbu. It was actually much easier than I thought it would be.

I was finally able to work on it this past weekend since I finished grad school last week.

I plan on doing a full recap in the near future after realizing how easy it is. Oh I also replaced the main 10,000 uF 50v power caps with some nichicon units while I was in there.

The only trouble I ran into is accessing the power board with the big transistors connected to the heat sinks in back. I didn't want to disconnect any of the board connecting wires (twisted ones) so I had to kink my neck.

After I replace some caps and transistors I plan on contacting the Radio-X guy an hour north in Flint, MI. I've read good things and I'm guessing my tuner could use some calibration alignment.

I look forward to future posts, for the recap I'll include some pics.

-jizawiz