Taking on the big dog - Recapping my new SX-1980

w1jim · Feb 11, 2011

I just picked up my new (to me) SX-1980 and am going to recap everything except for the 4 large power supply caps (unless it in fact needs that) before putting it into service.
I'll be primarily using Nichicon caps. All electrolytics and tantalums 1uf or less will be replaced with poly film caps. Larger tantalums will be replaced with electrolytics.

It appears that 2-3 of the transistors on the power regulator PCB have been replaced. Otherwise everything looks to be stock.

Likely I'll be replacing the indicator lamps with LEDs. The dial lamps I'll probably leave as incandescents.

Initially listening indicates that everything appears to be working fine and the tuner is exceptionally sensitive.

First picture shows the receiver with my morning cup of coffee atop it.

I have already recapped the equalizer PCB - before and after pictures are below.

2 - 2200uf / 10v
4 - 220uf / 35v
2 - 220uf / 6.3v
4 - 10uf / 50v orange LR type
2 - 2.2uf / 50v orange LR type

Stay tooned!

DaWoofer · Feb 11, 2011

When you say "equalizer board" are you referring to the phono board? And yes, those tuners are something special for a receiver aren't they??

w1jim · Feb 11, 2011

Pioneer calls it the "Equalizer Amplifier" but we know it's really the phono board.

I have most of the caps "in stock" and have some higher voltage ones on order for the power supply regulator and the amp boards. I'm looking forward to dive in deeper soon.

Overundr1 · Feb 12, 2011

Thanks for sharing the in progress pictures. It will be interesting to see the power supply board rework. (perhaps signs of thermal stress over the years).
I do not recall seeing a full 1980 recap documented in photos before.
-Lee

MarkNC · Feb 12, 2011

My assumption is that they call it the equalizer board in reference to the RIAA
phono equalization...as opposed to the the main, "flat" amp board.

-Mark

DaWoofer · Feb 12, 2011

I did a partial recap on the equalizer board when I first got my 1980. I replaced C11,12,13,14,15,16. C11,12 had shrunkin platic covering from heat I suppose but the problem was with either C12 or 13 as i forget which one. The symptoms were while playing a LP the treble would automatically become multiples louder after playing for a while. With the assistance of Markthefixer and Echowars who explained and pinpointed these culprits as part of the feedback network I was able to repair it. Of course I couldn't find polystyrene replacements but the replacements sound the same to me.
It would be great if you could do a walkthru with picks of your work cause as mentioned earlier, I don't believe one has been done on this unit. Also would be great is a list of all the replacement parts, as it seems to be rare as well. Are you also going to be replacing transistors as well as I believe there are some that are known to be a weak link. This post will be watched very closely I believe by many.

w1jim · Feb 12, 2011

Just back from the New England "FrankFest" get together and found a nice big box from Mouser outside so there's more to come soon.

I've never been an ace at documenting my projects but since it seems to be lacking for the SX-1980 I'll do my best.
Some nomenclature will be of my own ignorant choosing though.

Here's what I've replaced on the Phono Amplifier Equalization PCB (I've copied these to the original post):

2 - 2200uf / 10v
4 - 220uf / 35v
2 - 220uf / 6.3v
4 - 10uf / 50v orange LR type
2 - 2.2uf / 50v orange LR type

JimB

Jailtime · Feb 12, 2011

Wow, there's some stuff packed in that chassis pretty tight! Looks like those big caps on the equalizer board were exposed to some heat. Nice looking work on your recap.

markthefixer · Feb 13, 2011

Morning cup of coffee? :yikes:

That much caffeine would kill a horse.

The rest of it.... a VERY familiar view.

Whatcha gonna do about the EchoWars current source?

w1jim · Feb 13, 2011

MTF-
Thanks for the heads up regarding the "Current Source" issue. I reviewed some of MTF's posts and found his link to the diyAudio thread (http://www.diyaudio.com/forums/solid-state/92904-pioneer-sx-1980-regulator-driving-me-insane.html).
I am fortunate in that my SX-1980 (I love the sound of that phrase) seems to be fully functional so at least for the moment I'll just be focusing on the full recap and avoid any further modifications. The PS board on mine doesn't have any indications of heat stress (no discoloration) so I think I'm fortunate there. I do suspect that 2-3 of the TO220 cased transistors have been replaced based on their different appearance and excess thermal grease.
I will look at and consider the Pioneer bulletins for factory upgrades though.

DaWoofer · Feb 13, 2011

w1jim- what led you to recap the phono board, was it just first inline because you had the parts available?

w1jim · Feb 13, 2011

DaWoofer said:
w1jim- what led you to recap the phono board, was it just first inline because you had the parts available?

Low hanging fruit - it required the least disassembly and the quickest way for some cheap satisfaction :banana:

.
I had all but 5 caps in stock for the entire beast - the last 5 (plus some more general inventory) came in yesterday - so I'm good to go for the next step.

DaWoofer · Feb 13, 2011

I take it you do this for a living or income on the side of sort? To have all that in stock is quite an amateur's hoard. Are you using different grade caps for the signal path compared to the power supply side of things? You know, the big argument on if theres a difference in caps. I believe you mentioned that your PS board shows no sign of heat stress. Mine is the same way as I also feel fortunate in that regard because most of the photos I've seen show discoloration. How would you describe the "sound" of you unit right now? I'm really curious if there will be a change or if it will mostly end up being a "refresh of old part" so to speak. It to bad some sort of test besides our ears were available to reveal this besides distortion or power tests. Have you looked at your output on a scope to reveal any anomalies? Myself, besides DC offset ridding on the signal is the only thing I would be able to "see" on a scope as I'm unsure of any other scope tests relevant to its health except maybe voltages with a DMM of the power supply. Off hand, do you have an idea what the cost in parts will be when all parts are combined? I'll quite rambling on with all the questions and have a nice day!

tobyj17 · Feb 13, 2011

w1jim said:
Low hanging fruit - it required the least disassembly and the quickest way for some cheap satisfaction .
.

Or it's your OCCRD

(obsessive compulsive capacitor replacement disorder)

Seriously though, very nice receiver. Even though I'm a Sansui guy i'd love to get my hands on one of these. When are you going to tackle the rest of your G-22k? I'd like to see the same documentation you used for the Pioneer.

w1jim · Feb 13, 2011

DaWoofer said:
I take it you do this for a living or income on the side of sort? To have all that in stock is quite an amateur's hoard. ...I've an idea what the cost in parts will be when all parts are combined? I'll quite rambling on with all the questions and have a nice day!

As tobyj17 said - it's my OCCRD.

You should review the thread I have on comparing my 2 SX-850s-
http://www.audiokarma.org/forums/showthread.php?t=343405

I don't do this for a living although I do from time-to-time do basic repairs for friends. I've been an electronics hobbiest since my teens and have amassed a substantial amount of junque (or treasure :scratch2

. When it comes to parts like most caps it just makes more sense for me to buy a bunch of extras whenever I'm doing a project. It just makes life so much easier in times of saved time / postage and I reap the benefits of volume pricing. Besides there are only about 2 dozen values that I need to stock in capacitors - you don't need every single voltage, just a few normally will do.

I don't know off hand what the total cost of parts will be but most of these only cost ten to twenty five cents each. The poly caps are about fifty cents and the 3 big caps on the PS PCB are maybe a buck-fifty.

And now, see the next post....

w1jim · Feb 13, 2011

Power Supply Regulator

It's power supply Sunday!

Recapped the power supply regulator PCB today.
I noticed that on the reverse side of the PCB there were 2 reworks involving cutting of 2 traces and inserting 2 - 470 ohm resistors. I'm not sure if this was done at the factory or during a service event.

I replaced the 3 larger axial caps on the PCB with radial parts. I ordered the wrong configuration and decided to use these. Same function but I had to extend the leads, cover them in teflon tubing and a piece of heat shrink.

The parts list:

1 - 3300uf / 35v axial
2 - 220uf / 160v axial
6 - 100uf / 50v radial
2 - 100uf / 100v
1 - 10uf / 16v
2 - 10uf / 50v
1 - 47uf / 16v
3 - 100uf / 16v
2 - 100uf / 10v
1 - 100uf / 6.3v

And now for the pictures. First is before, then the reverse side after and the last are 2 views of the after.

markthefixer · Feb 14, 2011

You WILL PLEASE document the junction points that those resistors are connected to (and where the cut is), for the health and safety of your SX-1980.

To the best of my ability to reconstruct from those (and my) pictures. I suspect I am wrong, and really HOPE I am. I have spent too much of the little time I have today, on it already.

tarior · Feb 14, 2011

Are you gonna do something about those mismatched +/- 80V regulator transistors? Have you checked all of the regulated voltages yet? Somebody's been in there before, and the quality of their work is suspect.
Echowars' current source mod is worth its weight in gold, and I would do it on any other 1980 that I worked on; even it seemed like it didn't need it.

Sandy G · Feb 14, 2011

w1jim said:
I am fortunate in that my SX-1980 (I love the sound of that phrase) seems to be fully functional so at least for the moment I'll just be focusing on the full recap and avoid any further modifications.

Uhh...No disrespect or anything like that intended, but- Did you ever hear of the old saw, "If it ain't broke, don't fix it ?" Given the rarity/cost/desirability of SX-1980s, personally, I'd think long & hard B4 I went tearing into a functioning unit... My luck, somehow or another, I'd manage to screw up some Unobtainium part like the SX-1980-only Hydrostatic Gonkulator, & end up w/a very expensive "Dog-Pisser"/doorstop...Just sayin'.

w1jim · Feb 14, 2011

Here's what I can discern:

Q211 is the transistor with the excess thermal grease - it is a 2SB682 which appears to be the correct part number. The solder looks to be similar to the other connections so it may be original.

Q210 is the one above that on the heatsink. Stock part number is 2SD712 but there is a 2SC3890. I think this is an OK replacement. (Better specs with 500v vs 100v and 7a vs 4a). I have a 512-KSC2073TU I could put in there but I don't think it's necessary.

The cut traces - this is where it gets especially tricky between trying to read my service manual pictures and comparing it to the schematic.
As best I can determine the Q203/2SA628A base connection to the gate of Q207/3SK34 is interrupted with a 470 ohm resistor. The trace is cut and the resistor then is used to complete the circuit.

The same situation exists for Q206/2SC945A to Q208/2SK34.

Voltages appear good at +80.6/-79.2 and +35.2/-34.7.

And most importantly, while I'm still working on the recap, everything is working.

JimB

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