Pioneer SX-650, cleaned, recap, resolder - persistent trouble...

[jacobsteel]

I found a decent Pioneer SX-650 at a fleamarket (200 SEK ≈ $20), it wasn't all dead, but had to get service. Now I've given some attention to:

1) Mains switch (opened, oiled/deoxy = stays on solidly, without buzzing sounds now)
2) Lights (changed smaller to LED, larger to new bulbs (might go back to 8V bulbs on the two small, nicer)
3) Cleaned, deoxy, potentiometers, switches, etc.

However, I still had the persistent problem of the Left channel slowly fading down. Cranking up the volume, change song, could revive it to normal sound.

So I started a recap, thanks to this forum I stayed off all Radio capacitors and mainly changed electrolytics on:
Tone Control Assembly (AWG-049)
Power Assembly 1 (GWH-101)
Power Assembly 2 (GWR-101)

Quick-notes on decap:
Good order (taped all caps to a xerox of the schematics, marked all swapped, triple checked polarity).
Forceps (steady, lockable, grip) saved my day, good tools for grabbing tiny caps is essential.
Desoldering braid/wick = less old solder falling on other boards. Check function after each change (less to backtrack if things go south). Time? The above 3 boards, ≈ 30-40 caps ≈ 5 hrs.



BUT - I _still_ have the intermittent problem. Knocking/tapping on Power Assembly GWR-101 can provoke the dropouts, specifically even slight tapping on 2SD313 (both). I did resolder them, but could they have intermittent failure still? I'll try and get some cold spray and change them but questions remain:

1) If I can't get Q7, Q8, 2SD313 x 2 - what are the best replacements?
2) Should I also change Q10, 2SB207?

Thanks a bunch, great forum.

 

[elnaldo]

If your unit has protection relays at the output, dirty relays use to do what you describe. Tapping on them or turning up the volume and the sound comes back.

 

[jacobsteel]

Thank you! I will certainly try that.

I guess I got confused from the sound going down so gradually, with no cracks/pops.

 

[bberkom]

I had an sx-780 with a similar problem, and mine was the relay as well. There's a pioneer replacement relay thread somewhere that lists all the proper replacements.

 

[bberkom]

Found it.
http://www.audiokarma.org/forums/in...-relay-replacement.150439/page-2#post-6759577

 

[Tom B]

Definitely sounds like intermittant contacts in the protect relay

 

[jacobsteel]

Thank you, all!

--- Before ordering a new relay I decided to desolder the old one, clean it and check (pix).

= Intermittent silence was fixed (and the paper-strips show some dirt too). However (after replacing all electrolytes and cleaning all switches, relay, resoldering most of the amp boards), I _still_ have a "boiling" sound, not affected by Tone Control/Volume/Balance (= on the amp board).

Unfortunately I have no cold spray here (I'll get some). Any tips on likely culprits? Any known dodgy transistors?

 

[NAD80]

hello jacobsteel. Welcome to AK. Checked the SM against the "Top ten worst transistor thread. Found the Pioneer has the 2SA798, 2SC1344 transistors. Check the thread http://www.audiokarma.org/forums/in...hatever-and-replacements.731653/#post-9894728 . Those 2 transistors could be the noise you are hearing. Nice job on the relay

 

[elnaldo]

There is a whole thread about replacing the 2SA798 with 2 x 2sa992 .

 

[jacobsteel]

NAD80 - Thank you!

There is a whole thread about replacing the 2SA798 with 2 x 2sa992 .

- great, thanks - is this the one? http://audiokarma.org/forums/index....nsistor-2sa798-is-there-a-replacement.281614/

 

[elnaldo]

NAD80 - Thank you!

- great, thanks - is this the one? http://audiokarma.org/forums/index....nsistor-2sa798-is-there-a-replacement.281614/

Yes, that one. Unfortunately all my picts have dead links since "Dropbox" changed the "Public Folder" access to be "private, not public anymore. But it's plenty of info. Don't overthink about it. Just use matched ksa992 (or 2sa992) or some of the other transistors suggested in that thread.

 

[jacobsteel]

Update: Checking (very slight tapping w. wooden stick), board by board, i noticed something dodgy with the ToneControl (also after Volume, i.e. will add noise at zero volume, note to self: page 16-18 Service Manual).

Cleaned switches and pots again. Resoldered _everything_ on that board --- probably a good order, as resoldering also evaporates leftover cleaning fluids. Cleaned and retigthened pot bases to chassis. Tested again, run for one hour, test again w headphones as well.
= Apart from a small "click" when Treble passes 12'o clock it's silent now. No boiling, a bit of low hum and noise (as expected from non-balanced stuff) but way better than before.

Thanks again for all great advice!

 

[elnaldo]

Well done, resoldering use to solve many problems. If you ever hear some crackling noises , replace the 2sa798 too

 

[NAD80]

Nicely done . Glad it sound that good. Enjoy it.

 

[jacobsteel]

.. but wait... of course it came back (after 3-4 days of good behavior and relative silence*).

So I changed both 2SA798 to 4 BC560 (holes were already drilled and marked for 2 separate transistors on the board). But left channel intermittent noise/boiling/crackling remained. --- I tried to desolder pin 10 (R in) & 25 (L in), to isolate it on board GWH-101. By itself it seemed silent, but hey, last time it went away and came back after 3-4 days...

= Resoldered output of Tone board and input of Amp board for good measure. So far it stays quiet, yet I have a feeling this is an running thing... I'd like to isolate it on one board though.

* "Relative silence" = Recording @ zero volume through headphones looks alright via Audacity spectrum anyway. Not much hum actually.