Pacific's Pioneer SX-939 Restore (lotsa pics!)

[Pacific Stereo]

Well, another beauty is back to making music, this time, an SX-939. This was the last series of the blue-faced Pioneers. This particular unit was working, but the owner wanted a partial overhaul and recap, and of course there are some reliability changes to be made. So let's have a look.

The unit had seriously dirty and sticky switches and controls, and they were very intermittent, making listening impossible. And it was dirty. Really dirty. Cosmetically I knew it was good under the grunge, but dirty nonetheless. The inside will tell the story.



You can see the tiny-time-bomb 2SA809 and 2SC1451 (those are the silver TO-1 with integral heat-sink parts) transistors on the power amp board in the photo above. Plus, this thing is seriously dirty inside.



So basic cleanup is the first order of business. Since this owner wanted to economize a bit, he got a "get the job done" clean-up, which isn't quite as pretty as making them all sparkly, but certainly works fine. Now we can see a little bit better.



After cleaning up, I started to do some inspections. Discovered that for its entire life, this receiver has had a snubbing capacitor not soldered. This is not a particularly important problem and won't cause any outward symptoms, which is why it has never been caught. I lifted the part so you can see.



Inspection reveals something else a bit more significant. This model is a general-export version, so it has selectable input voltage. Unfortunately, this unit has been set to and run at 110V for its entire life, which puts too much voltage on the filter caps. It should have been set to 120V. This is the result. Of course, these can and do fail, but overvoltage definitely made it happen faster.



Eeeeeewe. Lee-Kee Slipyards! (Major kudos to anyone who knows this reference.) The electrolyte has corroded the wiring, too. Here's a close-up.



So we'll have to fix that first. Of course, modern parts are much smaller than the original parts.



So we have to do a little modification. I use pipe insulation to fill the gap between the new part and the clamp.



Here's the underside after rebuild of the power supply, protection circuits and installation of the new caps. Larger bleeder resistors are installed, too. In this case, I don't trust the foam to hold the parts, so some RTV on the bottom keeps the new caps secure.



After working on those areas, the power amplifier was then rebuilt. Film parts for the inputs were installed in the power amplifier stage, along with upgraded semiconductors where it matters, and new bias and offset pots. This customer did not want a full recap, so the tuner and control sections were left alone, with the exception of changing out a couple of electrolytics for film parts while I had the boards out for switch and control service. And now, obviously much cleaner!

Switches and controls are now dead-quiet, silky smooth and work and sound great.



The usual Pile-O-Parts:



And oh, is she pretty:





A look at the back:



So now, off she goes to make music for her very happy owner. I love this!




All photos, copyright ©2012 Pacific Stereo. All rights reserved, no use without written permission. I better not see these on eBay!

[Des-Lab]

Sometimes I wonder what's prettier: the gear or the background scenery.

Great pix!

[Elite-ist]

Those vintage of Pioneer SX receivers are nice to see back in their former glory. Nice job, PS! The SX-939 weighs in at a little more than 40 Lbs., so you made sure your posing table's hardware was nice and snug. These receivers, especially, look nice lit up. Run the extension cord out there.

Nando.

[Pacific Stereo]

Hah! That's a good idea. Too late in this case, but I'll definitely do it next time.

[Warped Bezel]

Darn...already owned.

[MRFLASHPORT]

Wow, another fine job PS. That is a beautiful receiver, I've always admired those series of mid 70s SX receivers. This was before Pioneer cheaped out on the later ones with STK packs. And your photography of it against that awesome sky leaves me speechless.

The owner will be blown away I am sure!

[Parnelly]

Originally Posted by Elite-ist

These receivers, especially, look nice lit up. Run the extension cord out there.

Nando.

Haha, funny you mention that Nando, as i was scrolling down through the pics and made it to mountainous pics I thought the exact same thing.

[Scorpion8]

Awesome writeup.

[Pacific Stereo]

Thanks, Scorp. This customer just picked up his 939 and has left a 434 in its place, so I'll be able take lit-up photos next time.

[HeadGap]

WOW!!.... Nice job on that one Pacific, another great rebuild and picture essay. That was a dirty one OK.
I’ve never really been a big Pioneer fan for some reason or other, but after seeing this rebuild I might half to change my thoughts on that.

OK I give up. The closest I can think is that the Slipyards are the rubber caps on the bottom of the capacitor?

Jeff

[StereoGaryo]

Simply gorgeous PS. I can't wait for you to do my 1250.

[Elite-ist]

That's worthy of being a Pioneer SX-939 tribute picture, PS.

Nando.

[dubber09]

Still trying to wrap my head around:

"So we'll have to fix that first. Of course, modern parts are much smaller than new parts."

[20tajk7]

Great job
Some months ago I've found a 838 that needs some servicing for 0€, but I've still not have started to fix it because my cassette decks collection takes me lots of time.

[Pacific Stereo]

Originally Posted by dubber09

Still trying to wrap my head around:

"So we'll have to fix that first. Of course, modern parts are much smaller than new parts."

Ha! That's called a typo. And it's now fixed. ;)

[Socal Sam]

Superb work and photography.

[dannyboy131973]

Wicked nice dude!

[JaeTee]

Very, very cool final photo....

That's a perfect photo series to represent "Pacific" Stereo !!!

Very well done, and seeing this presented this way makes me want to hear that Pioneer.

[Pacific Stereo]

Now it has a little brother, the SX-434 Mini Me!

[Elite-ist]

Hope it's not too early to congratulate you on making it to the forum's "Image Of the Week" with your outstanding Pioneer SX-939. It's not often you capture a shot like that.

Nando.