Working on an SX-1280

Jailtime

Standin' on a corner
This is the first Pioneer I've had the pleasure to work on. First impression: Sh*t this thing is heavy! :D This 1280 isn't mine, AKer joel27 picked it up recently.

These are just a few "before" pics. I think this was a smoker's unit, the faceplate and knobs are pretty grimy and yellowed. There's a few minor scratches, but this should clean up very nicely. I put that Def Leppard LP cover there to give a sense of scale. I've never seen a Pioneer monster receiver before, so I was pretty impressed by the literally beer can sized filter caps. Note the caps on the protection board, they have seen lots of heat in this 1280s lifetime.

The SX-1280 does work, it comes out of protect, and there's sound on both channels. Tuner seems to work in FM Stereo. The pots/switches are very dirty in it. I measured DC offset at about 90mV on both channels.

So, Pioneer folks, got any pointers for me? Like I said, this is the first Pioneer unit I've looked at. Worked on plenty of Marantz and a Soundcraftsmen before though. I know that the protection board is a weak spot in the 1280. Another thing: Does this have the same transformer/filters as a Spec 2?
 

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Another nudie of the 1280. Yeah, it's nasty in there. Not looking forward to cleaning up this mess.

Got the faceplate pulled off. 2 nuts and 2 screws, that's all it takes. Well, you'll need a 1.5mm allen wrench to free the volume and tuner knobs. I also removed the wood end caps on the faceplate so I can soak it in the sink.

It's a bit of a job to free up the tone control board. I'm getting access to that right now, the tone defeat switch is severely oxidized.
 

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Holy Moly that thing is dirty! How you clean that is beyond me ...

I am going to enjoy watching this thread and seeing your progress pics.

Cheers!
 
Cleaned up the faceplate and knobs last night, it's lookin' pretty good! Got the pots treated with Faderlube F5, hit the switches with Deoxit D5. No more scratchy sound or channel dropouts. Played some tunes for about 10 minutes, and checked around for hot spots in the receiver. I read somewhere that the power supply board in these runs smokin' hot, the author of that line wasn't joking.

Time to get a cap list together so I can make a big Digikey order. I'm going to work on the power supply (AWR-157), protect circuit (AWM-123), and amp boards (AWH-074) for now. The tuner and preamp sections are functional, so I'll take care of the critical stuff first.

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This one looks good beside the 1250 I'm trying to clean up now. There is a brown stain on the faceplate and all knobs. The side panels fell off when I loosened the screws. The glass is broken. The inside is filthy with dust and dead insects. All the knobs are out of index and the volume knob is stuck on about 90db on a Polk Monitor 7. The metal top is brown instead of black.and..pitted so it may be rust. The set screws that hold the volume control knob on are either damaged or an odd size since the 1.5mm allen wrench wont fit. Presented on e-bay as a functional unit and some creative photography made it look very nice. Filed a claim with e-bay/paypal and my credit card company:sigh::sigh:
 
Recomend rebuilding the power supply... Be careful with the STV diodes--leads break on them real easy.
 
Do a search of the various circuit boards ie AWx-xxx.And look for MTF's parts lists.
 
This one looks good beside the 1250 I'm trying to clean up now. There is a brown stain on the faceplate and all knobs. The side panels fell off when I loosened the screws. The glass is broken. The inside is filthy with dust and dead insects. All the knobs are out of index and the volume knob is stuck on about 90db on a Polk Monitor 7. The metal top is brown instead of black.and..pitted so it may be rust. The set screws that hold the volume control knob on are either damaged or an odd size since the 1.5mm allen wrench wont fit. Presented on e-bay as a functional unit and some creative photography made it look very nice. Filed a claim with e-bay/paypal and my credit card company:sigh::sigh:

The metal top is supposed to be brown. The volume control knob has two holes, make sure to check each for a set screw.
 
Recomend rebuilding the power supply... Be careful with the STV diodes--leads break on them real easy.

Yeah, this power supply is cooked pretty well. There's a few caps bulged completely out of their wraps. This one's not seeing power again until the PS is rebuilt.

Looks like there's only one of those damn STV diodes per channel. Easy access too, shouldn't have many issues with it.

Do a search of the various circuit boards ie AWx-xxx.And look for MTF's parts lists.

I searched the Pioneer forum using "SX 1280" as the search term. There's not much out there on these. I'll look deeper in MTF's threads.

Hopefully I'll find if there's any diodes/transistors that need to be replaced on that power supply board. EDIT: Found the parts list. I get to replace everything.
 
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That looks like a different unit than what I gave you. Good thing too. Might be a minute before it's ready to be heard again.
 
:lurk: I liked your Soundcraftsman thread better. More Angst! :D At least you still have wire wraps. Keep up the good work.
 
That looks like a different unit than what I gave you. Good thing too. Might be a minute before it's ready to be heard again.

Yeah, it's gonna be a minute or two. A complete power supply rebuild should be fun! :D I should do the tuner board, at least it's easy to get to!

:lurk: I liked your Soundcraftsman thread better. More Angst! :D At least you still have wire wraps. Keep up the good work.


Yeah, I'm not actually working on the 1280 yet. Just wait until I start replacing parts. There will be angst. :D Well, there's already angst brewing since some of the transistors I need for the power supply board are obsolete/non stocked.
 
Stay tuned, solder is about to be slung. Got a nice box of Panasonic FC and Nichicon caps from Mouser today. Few diodes and transistors thrown in for good measure.

I'm pretty much doing a complete power supply rebuild.
 
The metal top is supposed to be brown. The volume control knob has two holes, make sure to check each for a set screw.



I had the correct allen wrench but I had to stone a slight bevel/taper on before I could get it to fit the screws. After I scrubbed the top I found out that it is brown after all. The face plate and all knobs cleaned up and look very good.
One of the 22000uf caps is leaking. I don't know if I want to tackle restoring this beast or not.
 
Stay tuned, solder is about to be slung. Got a nice box of Panasonic FC and Nichicon caps from Mouser today. Few diodes and transistors thrown in for good measure.

I'm pretty much doing a complete power supply rebuild.

You do know how to flip the vertical boards in the chassis hole around for access?

Involves removing the two metal backing plates, and IIRC first flipping the protection board out - with appropriate harness loosening to accommodate this. Tight fit, but possible.

ends up with wonderful access to the bottom / top of boards - well worth the effort. I have done it several times.
 
You do know how to flip the vertical boards in the chassis hole around for access?

Involves removing the two metal backing plates, and IIRC first flipping the protection board out - with appropriate harness loosening to accommodate this. Tight fit, but possible.

ends up with wonderful access to the bottom / top of boards - well worth the effort. I have done it several times.

I was looking at that hole hoping I could do exactly this. I got the backing plate off the power supply board, I'll get to doing the same with the protect board. I just don't see a way to rebuild the boards without dropping them through the hole. Thanks for confirming that it's possible, Mark!
 
Now we're having fun! To free the protect board, you'll have to free those cable clamps on the heatsink and 4 or 5 on the chassis. Cut a couple cable ties if necessary, and take loads of pictures and notes, just in case a wire wrap breaks and you're left wondering where the hell it goes.

It was definitely worth the half hour of work to free these boards. They will be a piece of cake to work on now that they are free. Easy to clean up too. :thmbsp:

This board will be getting new Panasonic FC caps later tonight, hopefully. There's only 6 caps here, they aren't thoroughly cooked like those on the power supply board.
 

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Got the protect board recapped today, I also fixed a few bad solder joints on the board. Most of the caps on this board saw a jump in voltage, I consolidated my order to some more common values. So the 10uF caps are 50V now. They fit just fine.

I checked and double checked polarity on every cap I replaced. Gotta be sure everything is right, since I'm not putting this back together until the PS board is done.
 

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