Pioneer SX5 bad distorion - BOM avail?

quaddriver

120 What?'s per channel
Subscriber
I have not found a BOM for an SX5 here yet so I have done my own poking...

Subject machine: SX5, fully intact, works 'cept for real bad distortion on the right.

For S&G's I cleaned up the pots and did the suggested idle current set. Left, I was able to dial in to 23.5mv, but I set it lower to 21mv - this uses a steel heatsink rather than AL and is packed tight so I wanna err on the side of cool.

Right side, could not set idle to save anyones life, yet I have sound so peeking at the SM I conclude that the Q326 (2SB686) side of the dual emitter resistor aint got nothing on it.

I have my +/- rails of +37.8ish and -38. The schematic says +/- 35, the PCB board diagram says +33.5/-33.5

Thinking, uh oh, aint I a little high I look at the schematic for the rails and see:

upload_2017-2-22_10-42-58.png

Which tells me as usual, the rails are directly off the rectifying diodes so WYSIWYG. I have to assume this is ok right?

I have not checked the outputs of Q403/Q404 for the +/- voltages of the other stuff just yet...

Anyways...thinking Q326 has failed open I check 322 just before it and instead of the desired -1.2v I find -13.3v.

pic from manual that I used to test:
upload_2017-2-22_11-3-49.png

Using the left side as a template, yeah, that side is ok.

However, using speakers, the left side is not distorted, but it sounds tinnish to the point of perhaps a hi-freq scratch? Diff inputs?

I am off the mind to do both sides from the 2SA798s on in.

I have exactly 4 virginal 2SA798s from many many years ago. I will use them unless someone says "no, you must use KSA992s matched and flipped...

So amp only, and figuring a recap (and yes, all the resistors with triangles of death are still intact and functioning I can replace nontheless if ordered to do so)

I get:
Outputs:
Q325,326 = 2SB686, replace with either 2SB817 or 2STA1694 or ?
Q327,328 = 2SD716, replace with either 2SD1047 or 2STC4467 or ?

Digikey has both the STA/STC pair are half the price

Q321-324 sets of 2SA850/2SC1735 with 512-KSA1220AYS/512-KSC2690AYS

Q315-318 2SC2603 replace with KSC945C or KSC1815 (got a bunch of them)

Q307,308 2SC1845 replace with KSC1845

Q309,310 2SC2362 replace with KSC1845

Q313,314 JC501 replace with 2SC945A?? (this was a recommended onkyo fix from somewhere)

Q311,312,319,320 2SA1115 replace with???? Im drawing a blank here.....

And if I want to replace D306-309 (WZ046 - 4.6v zener) is there a preferred part?
and the plethora of 1S1555's...I know everyone uses 1N4148s, but I got a bajilion 1N914s which some say are 'electrically equivalent' - ok to use?

Any insights on the missing parts and comments on my selections thus far?

thanks guys...

edited to remove double pics and correct some tranny number typos
 
Last edited:
2SA1115 - so far I come up with KSA1015 and KSA733C all thinks being equal, ft = 175Mhz on the KSA733C, 80 on the 1015 and the original was 200

I think it was Mark who once said that on an NSA amp, speed is important. True case for these?
 
Had some time last night to hit the interwebs, this is my semi-conductor plan for the SX5.

Feel free to chime in. I will not order until monday most likely.

Outputs:
Q325,326 = 2SB686, Digikey 1026-2STA1694-CHP
Q327,328 = 2SD716, Digikey 1026-2STC4467-CHP

Q321-324 sets of 2SA850/2SC1735 with 512-KSA1220AYS / 512-KSC2690AYS (backorder from mouser so...)
Digikey KSA1220AYSFS-ND / KSC2690AYSFS-ND

Q315-318 2SC2603 replace with Mouser 512-KSC945CGBU or KSC1815 (got a bunch of them)

Q307,308 2SC1845 replace with Digikey KSC1845FTACT-ND

Q309,310 2SC2362 replace with Digikey KSC1845FTACT-ND

Q313,314 JC501 replace with Mouser 512-KSC945CGBU

Q311,312,319,320 2SA1115 replace with....Mouser 512-KSA733CGBU

I have the triangle of death resistors and there are a couple 4.6v zeners I have as Mouser 771-BZX79-C4V3113

I have my readers on to check for typos, but I think I got it all notated here.

Opinions?
 
got most my parts in, but had to re-order resistors. somewhere, somehow, something got morphed up, my 100ohm and 200ohm resistors (1/2w flame proof) got sent as 10 and 22. I gotta research who screwed up.

anyways, I took it apart and its easiest to just remove the whole heatsink and stuff as 1 part and it aint steel, its a weird finish (not paint, not adonizing) that makes it look like rolled steel. the NPN right channel driver had desoldered the collector. and who knows what else. the 5.6 ohm resistor is popped and I bet the diode and zener are gone too...we shall see.
 
I finally had some time and she spent the day:

IMG_20170322_144932_466.jpg

(burning in after a full amp rebuild)

These SX-singles are tight fitting mudders if you never got into one.

IMG_20170322_144940_142.jpg

As you can see the new outputs are smaller than the old, you see the grease smear where those large batwings fit. To work on these ya gotta take out the heatsink with the outputs attached one and all. Otherwise its annoying.

She got all silicon including all diodes, all triangle of death resistors, all caps, and all the other resistors were lifted and checked.

The old outputs are not technically blown, they are showing on my meter as still having a 30 something hfe. Anyone wants em, speak up. I did not test any of the upstream silicon, just pulled and replaced and the diff-inputs are factory original 2SA798s I still have leftover from about 15 years ago. The list in my previous post is what I used.

I just put the covers back on a few ago:

IMG_20170322_160817_429.jpg
This has the HP of a sx650/3600 but in half the case volume. They aint silver, they aint aluminum faced, they run hot, but they are real adult machine that sound just as good....
 
Well done and zero help from anyone here, congratulations. We are all lucky to have Digi-Key and Mouser supplying us parts to this day. Keep up the great work.

Cheers
Rick
 
thanks, Normally I can find parts lists for just about anything with the emblem and I lurk a lot, but the SX-singles are sparse save perhaps the 9 which MTF walked someone thru and I will someday get my PS rebuilt in mine (its such a pain I find excuses to do something else....)

but it all worked out. I would have done something WAY different for the heatsink, was I a pioneer engineer, its big, thick and clunky and sinks heat, more than bleeding it off...I even went low on the idle current to 20.5ish mv across the emitter resistor instead of the 23.5 and the damn PS - nuculah hot. I actually put a to220 sink on the negative side where it had nothing before. better safe than.... I surmise these machines are so rare cuz people stuck em in cabinets and they blorched the guts (technical term....)
 
Back
Top Bottom