WANTED: Repairs on Pioneer 950-SX

[gramophone-georg]

If I'm out of line by posting this, feel free to spank me and delete it, but I have a Pioneer SX-950 that I got new as a graduation gift from my parents. A couple years ago, I was listening to a late Isham Jones Brunswick record on my vintage 1930s RCA 2 speed transcription turntable through it when it suddenly sounded as though the needle just lost its tip- it started making a grinding/ scratching sound like a hip hop disc jockey got hold of it. I rushed over to see what was going on. The needle was fine and tracking OK but the Pioneer is now dead on one channel. Since my dad passed away last summer, I've been feeling more of a sentimental urge to get it back up and going again.

I'd like to know if anyone in the forum has any experience in repairing these. Figured I would start here.

Let me know via PM or email. Thanks!

[hearsedriver]

More than likely, it is a shorted or open output transistor. These come as pairs (one for the left and one for the right channel). Super simple to replace. They just plug in,. Replace them as a pair.

[gramophone-georg]

More than likely, it is a shorted or open output transistor. These come as pairs (one for the left and one for the right channel). Super simple to replace. They just plug in,. Replace them as a pair.

Where do you get 'em?

There's an outside chance that the transcription table caused the problem since it has a little tube sort- of preamp in it, but since it's mono and hooked up with a "Y" at the input on the Pioneer I'd assume it would have fried both channels if that were the case- correct?

Sorry... if it doesn't wind up I am clueless, LOL.

[hearsedriver]

Ebay has them .Toshiba 2SB557. First, I would check for any burned wiring on the circuit board or blown capacitors. These old caps go bad pretty frequently now. Im still leaning towards a transistor but, a loose transistor or jumper on the board will cause a lost channel also. A failed power supply can cause this too and it is not uncommon on these.

PS: Use thermal paste on the bottom of the transistors when you replace them.

[gramophone-georg]

Ebay has them .Toshiba 2SB557. First, I would check for any burned wiring on the circuit board or blown capacitors. These old caps go bad pretty frequently now. Im still leaning towards a transistor but, a loose transistor or jumper on the board will cause a lost channel also. A failed power supply can cause this too and it is not uncommon on these.

PS: Use thermal paste on the bottom of the transistors when you replace them.

I did pull it apart and check for that... no sign of anything amiss, really. I'll try the 2SB557s. Thanks!

[leadlike]

I would recommend finding a qualified service person in your area for blown outputs. Skimming over the service manual, it looks like you would have to redo the DC offsets and adjust the protection circuit before returning it to service. The service manual is available on HiFi Engine. You will need to set up a (free) account in order to view it.

Also, while I didn't follow the link to the Toshiba outputs, be aware that there is a huge market for counterfeit transistors, especially on NLA vintage types. I recently went through this over the summer on a receiver that used a special STK output. On any day on ebay there are vendors selling them, and after consulting some audio forums, was told that I would likely end up with counterfeits, and that hopefully the counterfeiter was using a good match. Well, the first one set the output board on fire, taking out some other parts. The second one I got from another vendor simply shorted and dumped 30 VDC straight into my speakers, and the third, while having the old part number obviously scraped off, is still currently working.

[gramophone-georg]

I would recommend finding a qualified service person in your area for blown outputs. Skimming over the service manual, it looks like you would have to redo the DC offsets and adjust the protection circuit before returning it to service. The service manual is available on HiFi Engine. You will need to set up a (free) account in order to view it.

Also, while I didn't follow the link to the Toshiba outputs, be aware that there is a huge market for counterfeit transistors, especially on NLA vintage types. I recently went through this over the summer on a receiver that used a special STK output. On any day on ebay there are vendors selling them, and after consulting some audio forums, was told that I would likely end up with counterfeits, and that hopefully the counterfeiter was using a good match. Well, the first one set the output board on fire, taking out some other parts. The second one I got from another vendor simply shorted and dumped 30 VDC straight into my speakers, and the third, while having the old part number obviously scraped off, is still currently working.

And that's precisely the problem.

[MTPhono]

+1 I HIGHLY recommend that you NOT attempt this repair unless you are knowledgeable and experienced. Your problem is much more likely to be related to capacitors or an output relay, not output transistors. There are qualified techs in nearly every city - find one. I'd recommend you go to a local record store, talk to people there - they will know who you should talk to. LP collectors like vintage equipment which requires good techs to service said equipment.

BTW - I just had my SX-1250 completely restored and it looks and sounds better than new. Replaced nearly every cap, several weak transistors and output relays. Love the big Pioneers!

I would recommend finding a qualified service person in your area for blown outputs. Skimming over the service manual, it looks like you would have to redo the DC offsets and adjust the protection circuit before returning it to service. The service manual is available on HiFi Engine. You will need to set up a (free) account in order to view it.

Also, while I didn't follow the link to the Toshiba outputs, be aware that there is a huge market for counterfeit transistors, especially on NLA vintage types. I recently went through this over the summer on a receiver that used a special STK output. On any day on ebay there are vendors selling them, and after consulting some audio forums, was told that I would likely end up with counterfeits, and that hopefully the counterfeiter was using a good match. Well, the first one set the output board on fire, taking out some other parts. The second one I got from another vendor simply shorted and dumped 30 VDC straight into my speakers, and the third, while having the old part number obviously scraped off, is still currently working.

[WDC]

I just invested 2 minutes for a quick Google search and found a repair shop in Eugene, OR. Now, I don't know this fellow but it seems to be a good starting point: http://www.stereoworkshopor.com/

You may want to sign up at HiFi-Engine to download the service manual for your amp, in case you don't have it: https://www.hifiengine.com/manual_libra ... -950.shtml

[phonojim]

Join the Antique Radio Forum http://antiqueradios.com/forums/index.phpand post your questions there. They have a section called Vintage Audio Equipment which is where you should post your questions. You should get a lot of good advice and also be able to find a qualified repair tech for your equipment if you need that.

Jim