• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

SX-850 - Worst Case Scenario

jumpingship

jumpingship

New Member
Total newbie here...

I bought my first vintage receiver today, a Pioneer SX-850 off Craigslist. It looked super clean, and I checked/tested all the inputs/lights/switches/etc at the residence of the seller. I decided to christen it with a test pressing of a 7" I'm putting out after I got it home. The sound was remarkable! Then, as soon as I was texting a photo to gloat to a friend, the audio cut out.

I admit I was cranking it pretty hard. It originally worked for about 20 minutes and then about another 30 seconds after I left it rest for 20 minutes.

Is there anything I can check before I begin cursing the world? I bought it from a family man (it looked like his wife was making him unload some toys). I got the impression he was trying to just break even on it and I paid $225.

I literally know zero about receivers but I am decent with electronics. My SL-1200 was the source when it cut out. The TT has a semi faulty RCA output that I've been meaning to get replaced. Could that have anything to do with it?
 
Register to hide this ad
Some old floor standing '80s technics. They are 8 ohms and were plugged in as A speakers.

I've tried the B as well now, but none seem to be working. I tried headphones too.

It was a really abrupt cutoff with the sound.
 
I've repaired a SX-850 with intermittent cuts, the problems were: differential pair transistors on the power amp, 2 transistors on the protection board, and some broken solder on the power supply board.

All this 3 problems seems common in this units.

After replacing the differential pair (source of crackling noises), the unit was getting into protection before the max power, like at 1/2 of the volume pot. After replacing 2 transistors in the protection board, it was stable, no more cuts.

I'd check DC offset (with a bad differential pair, it should be a bit high), bias current, and replace those transistors and visually check the PS board at least.

If the relay is not engaging, you'll need to measure DC at the output, but before the relay, so be careful, you need to identify the right pins and measure with th eunit ON, powered, don't do it if you are not experienced or you don't feel confident.
 
Hello,
You can try removing the bottom cover of the unit, to see if you blew any fuses, but chances are if any of the power supply fuses are blown, it is probably because of a shorted component somewhere. But if you see a fuse is blown, try to replace it (with the same type).

Other than that, I suggest that you let people know where you are from, and maybe someone can steer you to a decent repair person.

these are great units, but after 40 years, some parts change value, other parts strart to drift and go bad, other parts like in the power supplies start to fail because of years of heat buildup.Then cranking it, can be the straw that breaks the camels back.
 
If you're in Antarctica, repairs might be spendy. In SoCal, perhaps not so much.

Which all goes to point out the advantages of filling in your location in your personal profile.
 
FWIW, the one I repaired had a bad trimmer on the amp that tore up quite a few transistors.

So, a word of caution, I do not recommend tweaking the trimmers in a shotgun attempt at repair.


They are very good units and the price was good. Pushing vintage gear without getting a good service first is a gamble. Even with a good service, it may be asking a lot to push them hard. They are aged.

Having it repaired and even rebuilt is worth it if you can find a good vintage tech.
Shipping it to a rebuild capable tech is worth it also.

Its a long haul to me so hopefully someone closer can step up or knows of a good tech down there.
 
You must log in or register to reply here.
Back
Top Bottom