Pioneer SX-1050 receiver restoration

[electra225]

This may be my next project. Mine has a bum channel. It will work fine sometimes, sometimes the left channel cuts out, sometimes the left channel has a growl like you get putting your finger on the hot end of the volume control. I have watched videos on how to go thru one of these. It looks complicated, yet doable. The front ends seems to be okay. If I connect an amp to the "main in-pre out" connections, it works fine. So I am going to concentrate on the audio section. I need to find a schematic first thing. I am a total novice at solid state devices, so this will certainly be a different effort. I suspect it needs a good recap first thing. Has any of you gone thru something similar to this and do you have any tidbits of wisdom you'd like to offer?

[danrclem]

I have a non-working SX-1050 but I suspect that mine has blown output transistors. Maybe someday I'll get around to checking it out.

I'm just a tech wannabe so I'm not likely to be of much help. My first though was dirty controls but you said the preamp worked ok. Maybe a cold solder joint that separates when it gets hot? I also have a SX-750 that I quit using a few months ago because it would quit working when it got hot. I could let it cool off and then it would work again. I could smell it but couldn't pinpoint what was going on with just a visual check.

Hopefully somebody will chime in that actually knows what they're doing.

[electra225]

What little I have read and according to videos I have seen tells me the transistors are typically reliable. Solid state devices use electrolytic caps for coupling devices. I believe also that I have seen "rebuild kits" that include all the necessary capacitors for these receivers. I wonder if Sams has schematics for things like this?

[danrclem]

These links may help you some. I have done image searches for schematics but some of them are hard to see.

I was adjusting the DC Offset on my SX-1050 when it blew so it was 100% my fault. I don't think I shorted anything out with the screwdriver but may have. I now have a small coated screwdriver.

https://www.hifiengine.com/manual_libra ... 1050.shtml

https://audiokarma.org/forums/index.php ... ct.925512/

[Motorola minion]

Much better quality electrolytic caps were used in most receivers like this including Sansui, Marantz, Kenwood, etc.

Also note! that direct coupling is used between transistors. Complex feedback and bias networks do use capacitors and low ESR should be confirmed before embarking on a wholesale recap.

That said, I generally do not work on this level of equipment beyond cleaning switches, pots, connectors, etc. That task alone is nearly always sufficient. I just did a Marantz 2252, a fantastic piece. The last Marantz was a 2238, which one channel prematurely distorted slightly at higher volume. I was not able to repair it and returned to customer, citing poor availability of replacement transistors. Did not want the hassle of finding them!

The NPN and PNP silicon transistors (2SA, B, C, D prefixes) used by Pioneer and others are often particular designs that NTE, SK, etc. ABSOLUTELY cannot substitute. Ask anyone who has repaired a Sony TV

Sams is very little help with this type of electronics, hit or miss coverage so HW Sams' MHF series of books is not worth exploring. The websites in the last post are the best resources I have found.

There are two easy methods to suss out a sometimes-bad transistor; Freeze spray and a heat gun with small nozzle to heat only the suspect part.

[electra225]

Mine would probably benefit from some detailed troubleshooting. Your comment about dirty controls is well-taken. For a long time, when the left channel would cut out, I could move a speaker switch or the function switch or sometimes even the volume control and the left channel would cut back in. I have been watching YouTube videos on them, but they don't really help that much. I wish Uncle Doug would do a video on a SX-1050. If I do decide to dig into this thing, I may need a good ESR meter, then try to figure out what ESR actually is and what relationship to reality it has. At this moment, I believe ESR is an audiophool term. Each video mentions ESR and idle current. Research goes on. I can't hurt it and it will still sell unrestored and not working for pretty good money, so I don't have much to lose.

[electra225]

I've been doing some research on this amp. The more I read, the more confusing it becomes. First, I need to identify the issue. Second, I need to do some directed testing. Like you said, Dave, service literature is scarce, so I may have to just wing it. Where do I start? I could buy an ESR meter if I really need one. Maybe just recap the entire amp section? Would any of you guys like to embark on this journey and would be willing to walk me thru it?