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an sx-950 im trying to work on. any advice is appreciated.

Discussion in 'Pioneer Audio' started by wd409, Dec 18, 2017.

  1. wd409

    wd409 Super Member

    Messages:
    1,389
    Location:
    Mobile, Alabama
    hi guys, a friend brought a 950 to me yesterday that he wants me to try to fix for him, it looks like it has simply blown a channel but I intend to check the voltages on the power board as well to make sure those are ok, what mainly wondering about though, do you see it the way i see it? ive included some pictures..

    it looks like (according to the service manual, 150 ohm 1/2 watt) resistors burned when the outputs shorted.
    I took the shorted outputs out and tested them, they are indeed goners, i thought the thing MIGHT come out of protection with the outputs removed but it didnt, no relay click. ..i didnt think the resistors alone would prevent it from coming out of protection, that should be an open circuit at this point shouldnt it...

    anyway, im gonna eat breakfast and then start checking voltages and what not. ill also measure the nearby resistors that have soot/flame marks on them, and those regulators and diodes.

    also attached is a picture of the bottom side, which visually looks ok, nothing stood out as being burned.
     

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  2. wd409

    wd409 Super Member

    Messages:
    1,389
    Location:
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    the voltages on the power board are all what the manual said they should be, the big ceramic resistors all appear to be ok, the little regulators below the resistors, the ones with heatsinks on them, appear to be shorted but its really difficult to get in there with my probes, i cant be certain i wasnt brushing up against the heatsink with the probe. the ones to the left of them with no heatsinks on them, one of them seems ok but the other has a short between 2 of the pins.

    thats where im at so far.

    i have to do this in 'spurts' because of a back injury, doesnt let me be bent over like this for long periods. so ill post back later with any new findings.
     
  3. tsd71

    tsd71 RIP Tom Petty

    Messages:
    2,558
    Location:
    New Jersey
    at the very least, rebuild the entire power amp including the outputs and trimmers, while you are in there I would also rebuild the power supply.
     
    Bruno Primas likes this.
  4. wd409

    wd409 Super Member

    Messages:
    1,389
    Location:
    Mobile, Alabama
    regarding the electrolytics, i was planning to recommend doing that to the power amp and power supply boards, i could use recommendations on specific caps to use in the power amp. (i assume any old 105c panasonic or nichicon would be fine for the power supply?), he doesnt wanna do a full on restoration tho (neither do i tbh, im doing this for free) the trimpots i can prob do no prob.
     
  5. markthefixer

    markthefixer On Hiatus, dealing with Dad's estate full time Subscriber

    Messages:
    21,085
    Location:
    Bensenville,Illinois
    Please let's get the terminology closer - those transistors on the silver heat sinks on the power amp board are the drivers.

    That's carnage in that channel. The outputs are probably fried.

    Lift one leg of each resistor you test, especially the big white 0.5 ohm ones.

    From some old notes - parts numbers may not be fresh, and have different suffixes now:

    512-KSA992FBU Q2,Q4 diff 2sa726 (just in case - they're cheap!!)
    512-KSA1381ESTU Q6 pre-driver
    512-KSC3503dSTU Q8 pre-driver
    512-KSC2073TU Q10 driver
    512-KSA940tu Q12 driver
    863-MJ21195G pnp output
    863-MJ21196G npn output
    534-4662 to-3 mica insulators
    512-UF4004 D8 D10 fast diodes 400v 1a
    594-5083NW150R0J R37, R39 150 ohms 2 watts (trust me) emitter resistor *
    652-3386H-1-101LF VR4 bias 100 ohm 1 turn
    652-3266P-1-103LF VR2 offset 10k? 12 turn
    594-5083NW4R700J R43,R45,R47,R49 4.7 ohms 2 watts base resistor *
    * = substitute a 7 for the 8 in these numbers for 1 watt resistors.... -5073#####
    C1 1uf/25v 647-UPW1H010MDD 1/50 0.14 ea
    C3 2.2uf/25v 647-UPW2A2R2MDD 2.2/100v 0.16 ea
    C6 33uf/16v 647-UPW1H330MED 33/50 0.24 ea
    C11 330uf/10v 647-UPW1E331MPD6 330/25 0.28 ea
     
    Last edited: Dec 18, 2017
  6. wd409

    wd409 Super Member

    Messages:
    1,389
    Location:
    Mobile, Alabama
    that is an amazing amount of help, thanks mark.

    how close are those outputs to matching the original in sound? will they sound the same as the other channel if i leave the originals on that side?
     

     

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  7. slimecity

    slimecity Super Member

    Messages:
    2,996
    Location:
    New Zealand
    Yea as others state here - if you have ALL your outputs fried then you have a lot of work to do.

    I would check all the emitter resistors - the large white ones.

    Check the pre-drivers - the ones in the little heatsinks - remove them entirely from the board to test. Chances are some of these may also be fried.

    Also check the green and black larger transistors in your pic, sitting beside the pre-drivers.

    Replace all trimmers.

    I also wouldn't bother doing any recapping unless you have shorted caps from this event - concentrate on sorting out the transistor situation before you do any recapping

    Do you know what caused this meltdown?
     
    Last edited: Dec 18, 2017
  8. wd409

    wd409 Super Member

    Messages:
    1,389
    Location:
    Mobile, Alabama
    sadly I dont. im fixing this for a friend of a friend.

    I didnt get any information of that nature when he brought it out, like "i was messing with such and such and it lit up.." or "i was listening to it as normal and it went up on its own" i have no idea atm, ill ask though.
     
  9. markthefixer

    markthefixer On Hiatus, dealing with Dad's estate full time Subscriber

    Messages:
    21,085
    Location:
    Bensenville,Illinois
    That damage reverberated through the entire amp circuit. The ONLY semiconductor on that board that you should reuse is the thermal bias diode. IF the outputs ALL survived (those 4.7 ohm 1 watt base drive resistors MAY have saved them) then and ONLY then can you reuse them. If one is bad, they ALL get replaced.

    Like I am fond of saying, there was a race to destruction and the components that LOST when another blew first are ticking time bombs. The drivers Q10 & Q12 are toast - as evidenced by the 150 ohm resistors. Replacing Q2, Q4, Q6, Q8, D8 & D10 is a minimal expense compared to the frustration you will experience when it either doesn't work or blows again on power up, or the third time your friend slightly stresses that channel. ASK me how I know... (remember - when you are a professional, and on a payroll, callbacks are DEADLY to your livelihood and reputation)

    D2 & D4 are in safe spots and can stay. See - I AM reasonable...

    The two most likely causes are either Q2/Q4 dying first as they ARE a known troublemaker type, or the 100 ohm VR4 trimpot opening up (even for just a second!!).
     
    Last edited: Dec 18, 2017
    merlynski and slimecity like this.
  10. wd409

    wd409 Super Member

    Messages:
    1,389
    Location:
    Mobile, Alabama
    I had already convinced him all 4 outputs for that channel needed to be replaced, even those 2 that test ok on my meter, i told him i didnt trust them.
    ive made a part list on mouser with the components you mentioned, i do need to tweak it tho cuz i didnt x2 some of the things i should have x2'd
    2 of the items are backordered, so im gonna find an alternative for those, one of those caps and the diodes.

    what part numbers are Q 2 4 6 and 8? d8 and 10? i dont see them on your initial list.

    thanks for the assist btw. its very helpful.

    btw, when I get these parts and I install the new trimpots, are there any precautions i should take? like "turn them all the way this way before powering up" or anything like that?
     
  11. rcs16

    rcs16 Super Member

    Messages:
    3,939
    Location:
    Baldwin, Ontario, Canada
    here is my list, ecq-v are obsolete, some stuff is out of date too.

    AWH-050 (Power Amp Assy)
    C1,2 (2.2uF/25V,Electrolytic) CSSA 2R2M 25
    555-RFS50V2R2ME3#5 (2.2uF,20%,50V,-40 C to +85C,Radial,D:5 mm.L:11 mm,LS:2 mm $0.333
    667-ECQ-V1H225JL Film Capacitors 2.2uF,50V,5%.L:10.2 mm,W:7.9 mm,H:12mm,LS:7.5 mm $1.21
    647-UKL1H2R2MDDANA (2.2uF,20%,50V,-40C to +105C,Radial,D=5,L=11,lS:2 mm) $0.178
    C3,4 (1uf/25V,Electrolytic) CSSA 010M 25
    647-UPW1H010MDD (1u/50V/5mm)
    555-RFS50V010ME3#5
    667-ECQ-V1H105JL 1uf 50v stacked film metallized polyester - preferred, best possible sound - $0.68 ea
    C5,6 (33uf/16V,Electrolytic) CEA 330P 16
    647-UPW1H330MED (33u/50V/6.3mm)
    C11,12 (330uf/10v,Electrolytic) CEA 331P 10
    647-RR71C331MDN1 (Aluminum Organic Polymer Capacitors 16V 330uF 7Mohms Diameter:10 mm Lead Spacing:5 mm
    647-UPW1E331MPD6 (330u/25V/D=8mm L=15mm ls=3.5mm))
    555-RFS6V471MH5#5 (470uF 6.3V 20% Audio SILMIC II D=10mm L=20mm ls=5mm)
    Q1-4 (2SA726S-F,2SA763S-5) I/P diff
    512-KSA992FBU (hfe)"P"= 200~400, "F"=300~600, "E"=400~800
    Q5,6 (2SA818-Y,2SB527-C) Current Source (TO-126,EBC)
    512-KSA1381ESTU (300V,0.1A,150MHz,7W,TO-126,ECB)
    Q7,8 (2SC1628-Y,2SC1451-B) VAS (TO-126,EBC) complement KSA1381
    512-KSC3503DSTU (hfe)"C"=30~80, "D"=60~120, "E"=100~200, "F"=160~320 $0.611
    512-KSC3503DS
    (Obsolete 512-KSC3503ESTU)
    Q9,10 (2SD381-M) Pre-driver NPN TO-220
    512-KSC2073H2TU (hfe)"H1"=40~60, "H2"=60~125 (NPN,150 V,1.5A,4MHz,1.5/25W) $0.733
    863-MJE15030G (150V,8A,2/50W,30MHz) $1.38
    863-MJE15032G (250V,8A,2/50W,30MHz) $1.33
    863-MJE15034G (350V,8A,2/50W,30MHz) $1.56
    Q11,12 (2SB536-M) Pre-driver PNP TO-220
    512-KSA940TU (PNP,150 V,1.5A,4MHz,1.5/25W) $0.767
    863-MJE15031G (150V,8A,2/50W,30MHz) $1.38
    863-MJE15033G (250V,8A,2/50W,30MHz) $1.33
    863-MJE15035G (350V,8A,2/50W,30MHz) $1.56
    Q13-16 (2SD427-R) O/P (Q3,4,7,8)
    863-MJ21194G npn output, 250V,16A,250W,4MHz,TO-3 ($6.52)
    863-MJ21196G npn output, 250V,16A,250W,4MHz,TO-3 ($4.70)
    Q17-20 (2SB557-R) O/P (Q1,2,5,6)
    863-MJ21193G pnp output. 250V,16A,250W,4MHz,TO-3 ($6.52) (SOA: 2.5 A, 80 V, 1 Second)
    863-MJ21195G pnp output, 250V,16A,250W,4MHz,TO-3 ($4.70) (SOA: 3 A, 80 V, 1 Sec)
    D1-4 (1S2473)
    512-1N4148
    D5,6 (STV-4H)
    D7-10 (1S1885)
    512-UF4004 fast diodes 400v 1a
    534-4662 to-3 mica insulators
    R37-40 (150 ohms/2 watt)
    594-5083NW150R0J
    VR1,2 (Semi-fixed,10K-B,ACP-029)
    652-3266P-1-103LF offset 10k? 12 turn $4.43
    72-T63ZB-10K $3.80
    652-3296P-1-103LF $1.93
    VR3,4 (Semi-fixed,100-B,ACP-019)
    652-3386H-1-101LF bias 100 ohm 1 turn

    R43-50 (Metal Film/1W,RN1H 4R7K)
    594-5083NW4R700J 4.7 ohms 2 watts base resistor *
    * = substitute a 7 for the 8 in these numbers for 1 watt resistors.... -5073#####
    R51-58 (0.5/5W,WW,RT5B 0R5K) (trust me) emitter resistor *
    280-CR5-0.5-RC
    594-AC05W0R500J
    588-WHER50FET
     

     

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  12. markthefixer

    markthefixer On Hiatus, dealing with Dad's estate full time Subscriber

    Messages:
    21,085
    Location:
    Bensenville,Illinois
    yes, start the 100 ohm pot at zero ohms as measured in circuit - that eliminates any cw/ccw confusion.

    the 10k pot usually comes centered, so be sure it is at 5k & 5k,

    look up "TICKLING THE DRAGON'S TAIL" on the forum.

    and look at the list, it was written for the traditional left channel (odds) but i almost immediately renumbered it for the right channel (evens)
     
  13. wd409

    wd409 Super Member

    Messages:
    1,389
    Location:
    Mobile, Alabama
    ^ regarding this, nevermind, im a dumdum. guess i was too tired to comprehend anything. (night owl)

    ive also just recently realized, this service manual diagram is reversed from the picture i took, that was throwing me off for a sec too.

    anyway, im going over everything a third time to make sure i have the parts and quantities right. looks like all of this stuff will come to about $60, if he approves it maybe we'll get this thing up and running soon
     
  14. wd409

    wd409 Super Member

    Messages:
    1,389
    Location:
    Mobile, Alabama
    just to update, the parts for this came in yesterday. the next few days are supposed to be a lot warmer here too so thats good timing. ill keep yall posted on progress/questions along the way.

    on a side note, he brought a 1250 out yesterday as well. he thinks that one has a blown channel, but said he wasnt clear on the details. we'll see.
    side side note: 1250 is a big ole bastard itnt he, in my recent recollections of carrying the thing in i reckon its at least 5 feet wide and about 675lb
     
  15. wd409

    wd409 Super Member

    Messages:
    1,389
    Location:
    Mobile, Alabama
    hello again everyone, after an absence im back to working on this again, i have all the new parts for that board put in and tried to do a power up test to see if the relay would click but it did not, do the outputs have to be in for this model to come out of protection? or have i missed something.

    im including 2 pics, they're the same pic, the second one i scribbled on. green circles indicate parts i replaced.

    and yeah, ive noticed that yellow wire, too.;/
     

    Attached Files:

  16. rcs16

    rcs16 Super Member

    Messages:
    3,939
    Location:
    Baldwin, Ontario, Canada
    The o/p's do not need to be installed to DC balance. You should measure/report all the PS voltages and also the DCV on the PA o/p terminals 10 & 25.
    Also check/measure all the DCV in the PA sections. compare each channel against each other and against what is printed on the bog schematic
     

     

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  17. Motnick

    Motnick Active Member

    Messages:
    338
    Location:
    Wyandotte Michigan
    It looks like some of the transistor pin outs might be incorrect. Here is a picture of my 950 power amp board that I completed a month or so back. I see a couple of differences on your board. Maybe you can use these pictures to check your transistor pin outs?

    [​IMG]
    [​IMG]
     
    Last edited: May 8, 2018
  18. wd409

    wd409 Super Member

    Messages:
    1,389
    Location:
    Mobile, Alabama
    hmm, thats certainly possible, i just put them in facing the same way the original ones were facing
     
  19. wd409

    wd409 Super Member

    Messages:
    1,389
    Location:
    Mobile, Alabama
    the more i sit here and look at these pics the more confused about this i get, so i started with the tiniest of the lot the 2sa726's, i looked at the datasheet for the originals and for the replacements i ordered, they *appear* to be correct, emitter, collector, base. putting these in the way the original ones were facing (which i double checked against my "before" pictures that i took) appears to have been the right thing to do, yet yours are facing the other direction than mine are... thats, odd.


    edit: oh i get it now. thats a bottom view on the diagram of the original, and a top view of the replacement, emitter and base are backwards
     
    Last edited: May 8, 2018
  20. Motnick

    Motnick Active Member

    Messages:
    338
    Location:
    Wyandotte Michigan
    Several of the replacement transistors have a different pinout than the original transistors that you have replaced. I print out the data sheet for all of the replacement transistors and keep them on hand for quick reference.

    Like you have discovered, some of the original transistors will have a BCE configuration while the replacement has an ECB configuration. Take your time and have a look through the transistor data sheets and you should spot your mistakes.
     
    Last edited: May 8, 2018

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