Pioneer SX 939 Repair and Restore

Placed order with Mouser. Sorry this project is taking so long. A lot going on and trying to do too much as usual.
 
Edit: ALLERT ALLERT ALLERT. Please disregard the following. I think I figured out what I did wrong. It is as stupid and obvious as I thought. This is what I get for working tired and trying to hurry. I will report in Post #67 when I make the correction. Thank you for your patience. Argh.

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I'm working on the Control Board and I've run into a problem.

First I replaced the whole row of 16 capacitors down the center lengthwise. Powered up. Checked with tone switch on and off. Worked.

Then I moved to the next row where you've got the eight transistors and four 100uF capacitors..Tone OFF = good. Tone ON = hissssss.

Fiddle sticks.

I checked pinouts of transistors and capacitors coming out and all seemed to match up with markings on the board. I double checked orientations everything going in.

Took the transistors and capacitors back out and checked them with little Chinese tester.

Took extra care putting everything back in with respect to cleaning up pad and good solder joints.

I feel like there is something so obvious I am going to be highly embarassed. Like persistent pinout dyslexia. Or maybe one of the board markings is indeed wrong and I missed it during the original-parts-removal. I'm using KSC1845FTA for 2SC1312.

Note: unrelated aside here is that all four 100uF capacitors C29-30 and C45-46 seemed to have slightly bulging and slighly leaking undersides.

Pioneer SX 939 Control Board Glitch.jpg Pioneer SX 939 Control Board Suspect Caps.jpg
 
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What transistor subs did you use? Were those bulging 100uF caps low voltage united chemicon's by any chance?
Hey how're you. Thanks for reply.

I'm using KSC1845FTA for 2SC1312. I was making some edits to Post #63 when you transmitted Post #64. Added a couple images. There isn't a brand name that I can see but they look like United Chemicon to me. 100uF 10V.

KSA992FBTA for the 2SA725.
 
Hi, good thank you and yourself? Your transistor leg placement looks good to me, the lower one in your photo should be facing opposite to the other three l believe. So this hiss has only occurred after you replaced these transistors and the four 100uF caps?, bit strange. Are all wire wrapped connections still intact?

Yes l have had those same caps fail in a couple of units l have worked on lately.
 
Your transistor leg placement looks good to me, the lower one in your photo should be facing opposite to the other three l believe.
I'm good. thanks. Here's a picture that shows the board markings on that end transistor. I shot the collector leg out to the rear as in the other ones, which oriented the face 180 degrees from its two neighboring guys.
Pioneer SX 939 Control Board Glitch 2.jpg

So this hiss has only occurred after you replaced these transistors and the four 100uF caps?, bit strange.
I cannot swear to it. I thought I checked after I did the other capacitors but it IS possible I blanked out. That is to say, I am sure I powered up and checked for sound ... BUT ... it IS possible I did so only with the Tone lever in the Off position. e.g. possibly did not toggle Tone lever back and forth and it could have been in bypass position.

I rechecked by UPW Nichicon caps in the first row addressed for proper orientation on polarity. I will look again. The Kemet film caps are nonpolar, eh? If there was a soldering issue or a short or open on that side, likely would only one channel or the other be affected?

Are all wire wrapped connections still intact?
It IS possible there has been metal fatigue. The board has been moved a fair number of times. Preliminary check for continuity: wiggled wires while operating to no effect. Was thinking about taking voltages at schematic-identified nodes.
 
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Found the problem. Sheepish. I reversed the 1845s an 992s. Yes I'm not kidding. What a dope. I cannot believe it. I will report back when I've straightened them out.

OK. Reporting back now. That was it alright. We had NPNs where there were to be PNPs and PNPs where there were to be NPNs. Good grief. Back in business now. Thanks everyone for your patience and understanding.

A few more capacitors to do and the Control Amplifier will be finished and ready to put back in place.

Should mention controls cleaned and lubed.
 
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You must be getting to the pointy end of this rebuild?
My latest plan is to get arrested sent to prison for two years three squares a cot electronics study time and learn the Geman long sword.

Pioneer SX 939 Control Board Done.jpg

Next Up: Equalizer Amplifier

Next After That: 1) back to the power amplifier to fix the idle issue (new potentiometers and possibly matched long tail pairs depending); 2) tuner recap; and, lastly 3) final touches (one indicator lamp is out (FM) but might do all lamps not sure and debating whether to go hog wild and replace diodes here and there).
 
That board is looking nice.
Thank you mate.

OK so below pictured is the Equalizer Amplfier board. BEFORE ... AFTER.

It's angled out from the chassis 90 degrees propped out there on a wire holder -- set up for work.

I left the Q1-4 as this unit has 2SA763 in these spots (you may actually be able to read the markings on one or two of these center frame secone shot), not the 2SA725 ... so in this case we leave well enough alone. Others were substituted as speciied in our draft parts list.

BEFORE
Pioneer SX 939 Equalizer Before.jpg
AFTER
Pioneer SX 939 Equalizer After.jpg
 
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EQ board looking very good also. Just thought l would mention that l have had a few problems with 2SA763's lately, namely intermittant popping/crackling noises when factory installed in Marantz and Yamaha input differential pair positions.
 
Just thought l would mention that l have had a few problems with 2SA763's lately, namely intermittant popping/crackling noises when factory installed in Marantz and Yamaha input differential pair positions.
Thank you for mentioning this. Good to know. Making me lean further toward replacing them -- at least the long-tailed-pair in the power amplifier board -- even it it turns out the idle issue is in the old still original trimmers.
 
Your welcome, nothing worse than having it all back together and some little issue arises. Yeah would be a good move l think to replace the input pairs whether they are 726 or 763.
 
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test jig is okay if you are going to do bunches of them. all you need to do is measure bjt Vbe (DMM in diode test mode) and match Vbe to <2mV and you will be just fine.

Most test .691 Vbe in this here bag of a hundred KSA992FBU -- good to go.

Transistor Matching Vbe.jpg
 
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Next time order 512-KSA992FBTA ammo tape

You are so right. Better for the reading notation trick AND -- the way the legs are shaped in the FBTA configuration -- personally find so much more convenient to orient to the holes in a PCB, as compared with the 'straight legs' in the bulk version. Thanks for the suggestion!
 
hard to say, run them til they fail, zeners in PS do fail earlier than most others from my experience.
Damn they have there mfg processes down perfect to get such good matching, that is why they only have "F" hfe grade.
 
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