Pioneer SX-1250 rebuild

Rico126

Active Member
Greetings all. I am about to embark on the famed SX-1250 restoration, and figured to do it in an interactive way. It is my Uncle's daily driver; and since he got me into this hobby of listening to music I'd give him something back that sounds much better. I have experience building and restoring tube gear, and have repaired and soldered on PC boards as well.

The unit had a channel cutting out at times so I took out the relay and gave it a quick burnish and it fixed that problem. I then noticed that the indicator lights are out, so rather than take that board out again I figured to embark on rebuilding the entire thing. I read a bunch of the threads on this, and already bought the Mouser part list. I plan on doing a board every few days when I have free time, and then checking each step with a DBT before moving to the next one. I suppose the first question is which boards are best to start with? I intended to start with the power supply board and the one underneath with the fuses, and work my way around from there.

Any input is welcome, and I will post progress along the way.

Thanks
 

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Much luck to you. The 1250 is one of the easier receivers to work with. Unless you are able to do the re calibration on the tuner, it is usually best to leave it be. If you do replace the caps, chance are good that you will have to send it to someone with the needed tools to do the re calibration stuff.
 
Sounds like an okay plan.Probably will want to replace the speaker prot relay at some point in time. Leave the tuner til last.
Unless you are able to do the re calibration on the tuner, it is usually best to leave it be. If you do replace the caps, chance are good that you will have to send it to someone with the needed tools to do the re calibration stuff.
I ? if just changing ecaps in the tuner, will take it out of alignment. The only place where ecaps may affect alignment/adjustment, is in the stereo demod section, but the stereo pll adj is not very difficult to adj, it just needs to be centered in the capture range or measure/adj the osc freq.
 
The relay has been purchased, as it had been serviced before I got the unit. Yes the tuner will be last. I do have a scope and generator to align the tuner, and probably could figure it out, but it will take more reading to feel confident to do so.
 
I started with the protection board. Q5 and Q6 replacements were too big for holes, so carefully drilled so as not to damage traces on pc board. Crisis averted. New relay, 3 transistors, and 6 caps. Referred to the Mattsd post (Thanks), and it seemed to go smoothly. I figure power supply to be next, probably disconnect wire holders to get enough room to solder 4 new caps in. Enough for tonight though.
 

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Q5 and Q6 fit, flux residue reduces the hole just enough to make putting the leads in a pita...

Heating the solder pad will soften the flux.
 
Thanks Mark. Info wont help me, but hopefully the next guy reading will take notice. This morning I spent about 20 minutes recapping the power supply board (AWR-107) After disconnecting some of the wire holders it bent down enough to change the 4 caps. Did dim bulb test #1 and fired right up. Tonight I pulled the stabilizer board and it has been repaired before. Found 2 incorrect value caps and some questionable solder joints. Had time to do all the caps, clean the terminals with the old pencil eraser trick, and 2 transistors, the rest will wait until tomorrow night. It is a pretty involved board so I would rather not do it tired.
 

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Not working tired is a very good idea.

And the "heating" information WAS for the next guy...
 
That board took a couple hours total. I should have marked all the transistor datasheet pin outs on my list of parts, would have saved some time looking each up on the computer as I went along. Oh well. Put it back in and DB tested it. Bulb dim, and both relays clicked so all is well. Amp boards are next.
 

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Good work all over, however the original solder joints for the "bleeder resistors" R15, R16 (3.3k ohms 3 watts - orange color i the fabric sleeves) concern me, look kind of oxidized, especially the inner corner one.

Don't just add new solder, clean the joint out and start fresh - BUT BE CAREFUL, THE HEATING MAY HAVE LOOSENED THE FOIL - BOARD GLUE, in that case the green solder mask must be scraped away from the copper, until it hits glued foil, then carefully solder it back together with some wire reinforcement, EXTRA wire if the component lead will not reach comfortably.

A joint goes bad - develops resistance, and gets MORE heat than it would normally get from the component's natural heat load. That gives the grainy appearance.
 
Thanks Mark. I will definitely do that tonight. It's great to have a second set of eyes looking for things that I missed. You also made me realize that I need to take pictures that are more clear.

One of those transistors on that board controls the power to the speaker indicator lights, right? I forgot to see if they work. I thought about changing those to led, but I probably won't.

I have not purchased the 4 main caps yet. I read a lot of old posts for suppliers, but most supplies have dried up. Any ideas?
 
Stabilizer board cleaned and re-soldered where Mark recommended, as shown in first picture. Thanks again.

A little under an hour and two amp boards done...almost. Come to realize that somehow I did not get shipped the replacements for the 2 tants (AWH-048-A: C11: .22uF 10v CSZA: 667-ECQ-V1H224JL2 .22uF 50v). Here I thought copy and paste was pretty foolproof; Mouser must have been out and I didn't notice. I need to check the rest of the order before starting a new board. Darn. The amps were easy boards though, and a quick fix when replacements show up. On to the rest of the boards. I assume the rest be done without disconnecting the wound wires; just move the board into a position to work? It looks it to me, but I haven't touched any of it yet.
 

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No need to undo any wire wraps. All the boards can be restored without disconnecting them. Loosen the harness to gain access.
 
Thanks Zebulon. I figured as much.

Forgot to mention, after the stabilizer board resto the speaker indicator lights now work again.
 
OK, after 3 days away I am back to action. Took the face plate off and started maneuvering the boards around to work. The volume knob and the tuner knob are held on by hex key screws. One was pretty tight, I assume the over the years it seized in there. I thought for a moment the small wrench would break, but the screw broke free instead. The screws to remove the face plate are pretty self explanatory, as well as removing the boards. I started soldering the boards with the Pioneer standing on it's side at first, then did the flat amp with it laying down. Laying it down seemed easier; I tried it on the side just to make sure I didn't drop anything into the unit itself. You just have to watch the wires for tension that may make them snap, as the yellow wire on the one board did break on me.
 

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Moving the boards was made difficult by a blue wire that in my opinion should have been under the wiring harness. With it out of the way the boards would be able to move about 8" further. Do excuse me for not remembering the boards that the wire connected, as I did the work last night. Here are a few more pictures of it disassembled, as well as the blue wire that held back that harness.
 

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AWM-089, the filter amp board, is the first one I tackled last night. Real easy board, 6 pieces to solder in. Sorry about the blurry pic, the camera is hit or miss on the close up shots.
 

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AWG-041 wasn't bad to work on, just had a lot of parts. Take your time and match up the parts, and make sure all polarities match the board. Also, here is the yellow wire that broke and had to be soldered back on.
 

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AWS-094 and it's one cap so it will have to share this posting with AWG-042. The AWS-094 board for some reason I could not get it fully out, so I just lifted it enough to get the cap in. It is right on the edge so no big deal. The AWG-042 was a moderately difficult board as there was a lot of pieces in a little space. Two transistors were right under the black and white wires, rendering my de-soldering gun useless. In improvising I damaged a trace, but was able to solder the lead to another lead near it on the same trace.

All the work of today's posts was all done in one night. When doing that much it is very important, unless you are one who does these in your sleep, to check and double check polarity and such. It would be very easy to get comfortable and try to go faster but it is not worth it. Have your Re-cap list from the Mattsd post, the schematic and layout for the board you are working on, and the datasheets for the transistors on the board. You don't want to finish this board only to find you messed something up.

One last thing, make sure you check your order off against their packing slip when you get it. They shipped me one extra cap which I would have been going nuts trying to find out where I missed changing it.

Only the EQ board is left, as well as a re-visit to the power amp boards to replace the tants that were omitted from the order, and by then the 22,000 uf caps should have arrived via Mouser. Then some adjustments and hopefully some listening!
 

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