Pioneer SX-838: Major Repairs?

Good Day,

I recently got onto the vintage audio scene and picked up a few items, a QX-8000a which is functioning fairly well and a SX-838 which I got with the intention of tinkering with and possibly learning on since it was not functional.

After popping the SX open and giving it a thorough clean here is its condition:

*It has power, and there is power flowing to the Left channel speakers only,
*But there is no sound, tuner doesn't appear to work,
*once turned on you can here the static rise subtly in the left ch then something internal makes a soft click and the static cuts out, this can be repeated by turning it off and on again

I've visibly inspected all the fuses, which had some grime on them but appear fine, many of the contact points (or soldering points) have small little brass coloured spots (looks like tarnish) but show no other damage. In general the top half of the metal board (to which all component are attached)has lots of wear/oxidation but this appears isolated to the open metal portions where nothing is attached. underside is mint looking.

So is this a power supply issue? a Speaker relay issue? Or something else? I'm wondering if this is the sort of problem a complete novice could or should tackle? I don't really want to invest much in it as it's cosmetically fairly rough looking, probably not worth that much even if I was to get it humming again.

Still I wouldn't mind learning on it if it's not too complicated. Otherwise I will probably pull it appear and see if anyone needs the components (or should I just send it to the curb?)

Thanks for any advice or guidance!

Power supply, tone board, and protection board.

Probably need some transistors and caps replaced.

Have you cleaned the controls yet?

Rob

There is something bypassing the Protection Relay from the time you turn it on, until it clicks. Take some more pictures of the overall unit (covers included). These can help with diagnostics.

Find the RELAY and TAKE A PICTURE OF THE BOTTOM SOLDER SIDE! Sounds like someone tried bypassing it and gummed up the works. If so you may have blown outputs (possible reason for bypassing the relay) driver transistors, etc.

If you don't have the skill sets to solder, identify parts, etc. this is really a job for someone who understands these and can fix it right. It can be done but the learning curve is fairly steep and intrusive to sleep, etc.

How about adding your location to your profile. County/State would work. You might have an AK'er that is local who might be able to work on it for you.

I spy 2sc1451's...

Deoxit it first, after looking for serious meddling in the innards (bypassed protection relay)...

Thanks for the replies!

Yes, I've given it a thorough clean with Nu-trol control cleaner as recommended by another AK member since deoxit can't be found here in MTL, even had to drive across town to get it.

After looking at it closely again, the only area I can see where there seems to be new solder work is around the AC outlets under the relays. I've uploaded some higher res photos here: https://nicemarket.net/sx-838/

markthefixer said:

I spy 2sc1451's...

Deoxit it first, after looking for serious meddling in the innards (bypassed protection relay)...

Click to expand...

Oh man in the last pic from the link in post #5 you can just see the little bugger's sticking out from between the trimmers.

Come out, Come out, Where-ever you are, you little Buggers..........:uzi:

Hmm...not sure I follow, what exactly am I looking for sticking out between the trimmer pots? Could you refer me to a comparison photo?

The 2sc1451s.

Rob

These transistors, with their little metal round bodies. They're on Mark's most wanted list.

we need pictures of the bottom (and top) of the chassis between the power transformer and the power switch on the front panel, that's where the bottom of the protection relay is exposed. We have to see if somebody has deliberately shorted out the protection relay or if they have wedged (or rubber banded) it permanently closed.

If you have downloaded the 32 meg service manual look on page 12(top) and page 13(bottom) of 74 pages in the pdf file, it will show the power transformer, the single smaller upright cylinder capacitor next to it, and the 1" cubed (about!!) asr-007 protection relay, all will be sticking THROUGH the metal of the chassis.

Normally upon power up the unit should be SILENT for about 4 to 6 seconds, after which there will be a click and the speakers will be turned on.
THAT is done by the protection relay. ASR-007.

OK, slowly putting it together.

I've uploaded more detailed photos of the requested areas above and below the chassis. I don't see evidence of tampering around the protection relay (although not sure what that looks like) but it does appear to be newer solder compared with other points. As far as I can tell the legs on those transistors seem solid.

https://nicemarket.net/sx-838/

Thanks again for taking me though this.

The condition of the legs on the 2sc1451's are not the deciding factor here. The deciding factor on them is that they DO breakdown internally, sometimes catastrophically. replacing them will prevent wholesale replacement of almost every component on the board.

The RELAY is the CLEAR Rectangular box that has "TYPE " printed on the top. It is controlled by the Protection circuit which senses DC Current or lack of DC Current in the output lines from the amp to the speakers. If there is a DC component in the current above a certain level, the protection circuit will NOT engage the relay.

Need you to look at the relay bottom and decipher the pins. Each pin has a number to it. The pins with a wire (lead) go back to a pin on the board or to the speaker switch. What you need to do is ascertain where each wire goes from the relay.

RELAY.............Wire Color and size (L or Sm)............Origin (Board and pin #)
Pin 1
Pin 2
Pin 3
Pin 4
Pin 5
Pin 6
Pin 7
Pin 8
Pin 9
Pin 10
Pin 11
Pin 12
Pin 13
Pin 14

NOTE: If the pin is UNUSED write in "N/C" for not connected. Other wise note color of wire and trace it back to it's origin. Note the board # and pin #. If it goes to the spkr or spkr switch note as spkr (R or L) or SPKR SW. You'll need to break open the wire bundles (cut the wire ties or open them up) to trace back correctly as there are more than one wire with the same color in most bundles.

The amp board is AWH-031-(A) There may be a different suffix (ie; B,C, etc.)
Protection Circuit board is AWM-025-C.
The board Number is rubber stamped o nthe component side of the board along one edge.

OK. I've traced all the wires connecting the speaker switch board and relay etc.:

I've indicated where they all go directly on the photos on the link above. The only thing I can see that looks out of place is the black wire coming from #2 on the switch board that leads to the electrolytic capacitors.

There is only one numbered pin on the switch board not in use (#3) and no #14. One other unused pin is marked as #0.

Thanks again for all the detailed instructions!