SX-850 Restoration Record

Discussion in 'Pioneer Audio' started by davros, Jul 20, 2018.

  1. davros

    davros AK Subscriber Subscriber

    Messages:
    184
    Location:
    Winston Salem NC
    So I have put off restoring my SX-850 while I "sharpen" my skills. With the exception of some minor circuit board repairs I have made little progress. Tube amps is the limit of my proficiency so far, but I'm going to go in head first and start this project anyway.

    Feel free to pipe in and throw out advice, it is both welcome and I am looking for it!

    My plan is to begin with a thorough cleaning and Deoxit job and verify current operation. It works now but it is scratchy at best. I am then going to begin with a recap, and replacement of known faulty transistors. I have a pretty complete BOM that I will be posting below. I have all of the items on hand at the start of the project.

    My first restoration step will be to replace the Capacitors in the power supply (Board AWR101)
    Then test operation
    Second step is to replace the known "Bad Actor" Transistors
    Then test operation

    I will repeat this with the following boards in the following order...
    Equalizer Amp Board (AWF-011)
    Flat Amp Board (AWG-038)
    Tone Amp Board (AWG-039)
    Protection Board (AWM-062)
    Filter Cap Replacement
    Switch Assembly Board (AWS-094)
    Power Amp Board (AWH-059)

    The power Amp board looks to be the toughest one and the end of the chain, so to speak. Following that I will adjust DC offsets and Idle currents.

    Start.jpg
     
    Last edited: Jul 26, 2018
    dlucy likes this.

     

    Please register to disable this ad.

  2. davros

    davros AK Subscriber Subscriber

    Messages:
    184
    Location:
    Winston Salem NC
    Power Amp Board (AWH-059)

    AWH-059: C1: 2.2uF 25v CSSA: 647-UKL1H2R2KDDANA 2.2uF 50v
    AWH-059: C2: 2.2uF 25v CSSA: 647-UKL1H2R2KDDANA 2.2uF 50v
    AWH-059: C3: 1uF 25v CSSA: 647-UKL2A010KDD 1uF 100V
    AWH-059: C4: 1uF 25v CSSA: 647-UKL2A010KDD 1uF 100V
    AWH-059: C5: 33uF 16v CEA: 647-UPW1C330MDD 33uF 16v
    AWH-059: C6: 33uF 16v CEA: 647-UPW1C330MDD 33uF 16v
    AWH-059: C11: 330uF 10v CEA: 647-UPW1A331MPD 330uF 10v
    AWH-059: C12: 330uF 10v CEA: 647-UPW1A331MPD 330uF 10v
    AWH-059: Q1: 2SA726: 512-KSA992FBU
    AWH-059: Q2: 2SA726: 512-KSA992FBU
    AWH-059: Q3: 2SA726: 512-KSA992FBU
    AWH-059: Q4: 2SA726: 512-KSA992FBU
    AWH-059: Q5: 512-KSA1381ESTU
    AWH-059: Q6: 512-KSA1381ESTU
    AWH-059: Q7: 512-KSC3503DS
    AWH-059: Q8: 512-KSC3503DS
    AWH-059: Q9: 512-KSC2073H2TU
    AWH-059: vr1 10k multi 652-3296P-1-103LF
    AWH-059: vr2 10k multi 652-3296P-1-103LF
    AWH-059: vr3 100 single 652-3386W-1-101LF
    AWH-059: vr4 100 single 652-3386W-1-101LF
    AWH-059: d7 1s1885 512-UF4004
    AWH-059: d8 1s1885 512-UF4004
    AWH-059: d9 1s1885 512-UF4004
    AWH-059: d10 1s1885 512-UF4004

    Power Supply Board (AWR-101)

    AWR-101: C10: 470uF 80v ACH-038, CEA: 647-UHE2A471MHD 470uF 100v
    AWR-101: C11: 470uF 80v ACH-038, CEA: 647-UHE2A471MHD 470uF 100v
    AWR-101: C12: 2200uF 35v ACH-060, CEA: 647-UPW1V222MHD6TN 2200uF 35v
    AWR-101: C13: 1000uF 25v CEA: 647-UPW1E102MPD6 1000uF 25v
    AWR-101: C14: 220uF 10v CEA: 647-UPW1V221MPD 220uF 35v
    AWR-101: C15: 470uF 63v CEA: 647-UPW1J471MHD 470uF 63v
    AWR-101: C16: 47uF 16v CEA: 647-UPW1V470MED 47uF 35v
    AWR-101: C18: 47uF 50v CEA: 647-UPW1H470MED 47uF 50v
    AWR-101: C19: 47uF 35v CEA: 647-UPW1V470MED 47uF 35v
    AWR-101: C20: 100uF 63v CEA: 647-UPW1J101MPD6 100uF 63v
    AWR-101: C21: 47uF 16v CEA: 647-UPW1V470MED 47uF 35v
    AWR-101: C23: 100uF 35v CEA: 647-UPW1V101MPD 100uF 35v
    AWR-101:Q1: 2SD313P 863-MJE15032G
    AWR-101:Q10: 2SC869 512-KSC2383YTA
    AWR-101:Q2: 2SB507P 863-MJE15033G
    AWR-101:Q3: 2SC1318,2SC869 512-KSC2383YTA
    AWR-101:Q4: 2SA720 512-KSA1013YBU
    AWR-101:Q5: 2SC1318 512-KSC2690AYS
    AWR-101:Q6: 2SA720 512-KSA1013YBU
    AWR-101:Q7: 2SC1318 512-KSC2383YTA
    AWR-101:Q8: 2SD313P 863-MJE15032G
    AWR-101:Q9: 2SD313P 863-MJE15032G

    Equalizer Amp Board (AWF-011) (Check board number, the “B” version of this board has two 100uF 6.3v caps in addition to the ones listed below)

    AWF-011: C1: 1uF 25v CSSA: 647-UKL2A010KDD 1uF 100V
    AWF-011: C2: 1uF 25v CSSA: 647-UKL2A010KDD 1uF 100V
    AWF-011: C7: 330uF 6.8v CEA: 647-UPW1A331MPD 330uF 10v
    AWF-011: C8: 330uF 6.8v CEA: 647-UPW1A331MPD 330uF 10v
    AWF-011: C11: 3.3uF 25v CEANL: 647-UKL1H3R3KDDANA 3.3uF 50v
    AWF-011: C12: 3.3uF 25v CEANL: 647-UKL1H3R3KDDANA 3.3uF 50v
    AWF-011: C17 100uF 35v CEA: 647-UPW1V101MPD 100uF 35v
    AWF-011: C18: 220uF 25v CEA: 647-UPW1V221MPD 220uF 35v
    AWF-011: Q1: 2SA725: 512-KSA992FBU
    AWF-011: Q2: 2SA725: 512-KSA992FBU
    AWF-011: Q3: 2SC1313: 512-KSC1845FTA
    AWF-011: Q4: 2SC1313: 512-KSC1845FTA
    AWF-011: Q5: 2SC1313: 512-KSC1845FTA
    AWF-011: Q6: 2SC1313: 512-KSC1845FTA

    Switch Assembly Board (AWS-094)

    AWS-094: C1: 220uF 6.8v CEA: 647-UPW1A221MED 220uF 10v

    Flat Amp Board (AWG-038)

    AWG-038: C1: 2.2uF 50v CEANL(NL): 647-UKL1H2R2KDDANA 2.2uF 50v
    AWG-038: C2: 2.2uF 50v CEANL(NL): 647-UKL1H2R2KDDANA 2.2uF 50v
    AWG-038: C5: 4.7uF 50v CEANL(NL): 647-UKL1H4R7KDDANA 4.7uF 50v
    AWG-038: C6: 4.7uF 50v CEANL(NL): 647-UKL1H4R7KDDANA 4.7uF 50v
    AWG-038: C13: 220uF 35v CEA: 647-UPW1V221MPD 220uF 35v
    AWG-038: C14: 220uF 35v CEA: 647-UPW1V221MPD 220uF 35v
    AWG-038: C17: 10uF 25v CSZA: 647-UKL1E100KDDANA 10uF 25v
    AWG-038: C18: 10uF 25v CSZA: 647-UKL1E100KDDANA 10uF 25v
    AWG-038: C23: 4.7uF 50v CEANL(NL): 647-UKL1H4R7KDDANA 4.7uF 50v
    AWG-038: C24: 4.7uF 50v CEANL(NL): 647-UKL1H4R7KDDANA 4.7uF 50v
    AWG-038: C25: 100uF 10v CEANL(NL): 647-UKL1C101MPDANA 100uF 16v
    AWG-038: C26: 100uF 10v CEANL(NL): 647-UKL1C101MPDANA 100uF 16v
    AWG-038: C27: 100uF 50v CEA: 647-UPW1H101MPD 100uF 50v
    AWG-038:Q1: 2SC1885: 512-KSC2383YTA
    AWG-038:Q2: 2SC1885: 512-KSC2383YTA
    AWG-038: Q5: 2SA725: 512-KSA992FBU
    AWG-038: Q6: 2SA725: 512-KSA992FBU

    Tone Amp Board (AWG-039)

    AWG-039: C13: 2.2uF 25v CSZA: 647-UKL1H2R2KDDANA 2.2uF 50v
    AWG-039: C14: 2.2uF 25v CSZA: 647-UKL1H2R2KDDANA 2.2uF 50v
    AWG-039: C15: 2.2uF 25v CSZA: 647-UKL1H2R2KDDANA 2.2uF 50v
    AWG-039: C16: 2.2uF 25v CSZA: 647-UKL1H2R2KDDANA 2.2uF 50v
    AWG-039: C19: 100uF 10v CEANL(NL): 647-UKL1C101MPDANA 100uF 16v
    AWG-039: C20: 100uF 10v CEANL(NL): 647-UKL1C101MPDANA 100uF 16v
    AWG-039: C21: 47uF 35v CEA: 647-UPW1V470MED 47uF 35v
    AWG-039: C22: 47uF 35v CEA: 647-UPW1V470MED 47uF 35v
    AWG-039: C23: 2.2uF 25v CSZA: 647-UKL1H2R2KDDANA 2.2uF 50v
    AWG-039: C24: 2.2uF 25v CSZA: 647-UKL1H2R2KDDANA 2.2uF 50v
    AWG-039: C25: .22uF 35v CSZA: 505-MKS2C032201BKI00 .22uF 63v
    AWG-039: C26: .22uF 35v CSZA: 505-MKS2C032201BKI00 .22uF 63v
    AWG-039: C29: 10uF 25v CSZA: 647-UKL1E100KDDANA 10uF 25v
    AWG-039: C30: 10uF 25v CSZA: 647-UKL1E100KDDANA 10uF 25v
    AWG-039:Q1: 2SC1312: 512-KSC1845FTA
    AWG-039:Q2: 2SC1312: 512-KSC1845FTA

    Protection Board (AWM-062)

    AWM-062: C1: .22uF 10v CSSA: 505-MKS2C032201BKI00 .22uF 63v
    AWM-062: C2: .22uF 10v CSSA: 505-MKS2C032201BKI00 .22uF 63v
    AWM-062: C3: 330uF 6.8v CEA: 647-UPW1A331MPD 330uF 10v
    AWM-062: C4: 330uF 6.8v CEA: 647-UPW1A331MPD 330uF 10v
    AWM-062: C5: 4.7uF 25v CEA: 647-UPW1V4R7MDD 4.7uF 35v
    AWM-062: C6: 100uF 16v CEA: 647-UPW1V101MPD 100uF 35v
    AWM-062:Q1: 2SC869: 2SC945A 512-KSC1845FTA
    AWM-062:Q2: 2SC869: 2SC945A 512-KSC1845FTA
    AWM-062:Q3: 2SC869: 2SC945A 512-KSC1845FTA
    AWM-062:Q4: 2SC869: 2SC945A 512-KSC1845FTA
    AWM-062:Q5: 2SA733: 512-KSA992FBU
    AWM-062: Q6: 2SC945: 512-KSC2383YTA
    AWM-062:Q7: 2SC1384: 512-KSC2690AYS

    Filter Capacitor replacement:

    E36D750MLN183TC79M

    Misc

    Avvid Thermalcote: 532-250
    Mica insulators
    TO-3 Mica Insulator: 532-56-03-8G
    TO-204 Insulator: 749-TO-204-100
    TO-220 Mica Insulator: 534-4672
    TO-220 Shoulder Washer: 532-7721-7PPS
     
  3. davros

    davros AK Subscriber Subscriber

    Messages:
    184
    Location:
    Winston Salem NC
    Switches have been cleaned, and the scratchiness is gone.

    Power supply board AWR-101 has been Re-Capped. Voltages are as follows...

    Pin............Schematic voltage....Actual Voltage
    Pin 2,3.........5.4V........................5.1V
    Pin 4,5........13.9.........................13.3V
    Pin 6,7.........51.5V......................50.2V
    Pin 8,9,10....36.5V......................35.4V
    Pin 11..........28V.........................27.1V
    Pin 13.........-13.5V......................-13.1V
    Pin 14..........-51.5V.....................-51.3V
    Pin 15..........-19V........................-18.9V

    Across the board all of the voltages are slightly low. But they seem close.

    I have all of the Transistors to replace the originals, but am undecided if I am going to replace them. I ordered the transistors due to low cost and high shipping, and to have them on hand if there is trouble.

    Any Opinions?

    20180721_165134.jpg
     
  4. davros

    davros AK Subscriber Subscriber

    Messages:
    184
    Location:
    Winston Salem NC
    20180723_194431.jpg

    Current status is as follows

    Power Supply Board (AWR-101) has been recapped
    Protection Board (AWM-062) has been recapped

    All systems still check out, Voltages are the same as reported above, and the radio station comes in loud and clear. Volume knob has become scratchy again, and will need another Deoxit treatment.

    Tomorrow will be the recap of Equalizer Amp Board (AWF-011), as well as the replacement of Q1 and Q2, 2SA725 (Guaranteed Failures as per MTF) with 512-KSA992FBU

    As I am now getting up close with this unit, I can't help but notice that with the exception of a little dust, this unit looks brand new internally. Every resistor is shiny, and there is no signs of heat or stress anywhere. Even the protection relay looks brand new internally.

    My knowledge of this unit is that it has sat unused since 1999 when the previous owners husband passed away. He died in his 80's and she in her 90's, so chances are it wasn't driven hard or abused.

    My though is that it is very "low mileage", and its biggest concern is old Capacitors. So far nearly every capacitor is pushing it's 20% limit, and many of the smaller values are off by 30% or more.

    So after some consideration I am going to hold off on any "Shotgunning" of transistors. I will replace the 2SA725 and 2SA726 as they are known failure points. And continue with the recapping. All of the replacement parts are here if needed, and can be put aside. I will also be replacing the thermal paste as a it just makes sense.
     
    Last edited: Jul 25, 2018
  5. davros

    davros AK Subscriber Subscriber

    Messages:
    184
    Location:
    Winston Salem NC
    As a side note, This is the first time I have used Kester eutectic (63/37) Solder (By recommendation). My solder skills have either vastly improved, or this stuff is so much easier to work with.

    I also bought a cheap Tenma Desoldering station, and once I got the hang of it, it's indispensable.

    I sell no parts or equipment, and have no interest in either company, these items have just have made this project more fun by making it less work and more hobby...
     
  6. davros

    davros AK Subscriber Subscriber

    Messages:
    184
    Location:
    Winston Salem NC
    Tonight I recapped AWF-011, and replaced the 2SA725 With 512-KSA992FBU.

    As a note, the Schematic, and Parts list in the manual showed a 2SA725, but both were marked A726. As they have the same substitute it was probably no big deal when it was assembled at the factory.

    The 2SA725 is BCE
    The 512-KSA992FBU is ECB

    Easy enough to just flip the transistor to reverse the Base and Emitter.

    No test was conducted today. It may be called the "Equalizer Amp Board" but I believe it is used for the phono imputs, and a radio test would not prove anything.

    011.jpg -011.jpg
     

     

    Please register to disable this ad.

  7. buttahman

    buttahman Active Member

    Messages:
    164
    Location:
    VA
    Looking good. Some things to watch out for when you get into the power amp:
    Watch out for those thermal bias diodes, they are quite fragile and difficult to repair/replace.
    As you're working on the board watch the wires leading to the outputs as they can/will break easily.
     
    dlucy likes this.
  8. davros

    davros AK Subscriber Subscriber

    Messages:
    184
    Location:
    Winston Salem NC
    I'll be careful with the Bias Diodes, I don't want to go down that road. I've seen some of the posts where people have to fix them and it doesn't look ideal at all.

    I'm not rushing, and doing an hour or two a day. The power Amp board will be my last board to recap, and I only plan to replace the four 2SA726, and the Bias Pots.

    At that point I plan to follow the procedure from the SX-950 Manual. I will probable do a search and look for a step by step posting on the site somewhere. I swear I saw one at some point, but heck if I can find it now....
     
  9. Watthour

    Watthour Electron Rancher - JS3600

    I would tend to agree. Provided you replace all the known "problem children" it would be tempting to let the other, original components live on. The 726s/725s, Sanyo blue aluminium teardrops, etc.
     
  10. zebulon1

    zebulon1 Getting behind on work. I need help? Subscriber

    Messages:
    4,790
    Location:
    Las Vegas Nevada
    I agree as well. I'll replace some TO-220 package devices in the power supply (Generally). Mainly the ones attached to heatsinks. Peace of mind would explain it.
     
  11. Watthour

    Watthour Electron Rancher - JS3600

    I would leave Q10 alone, but consider MJE15031G in place of the 507, MJE15030G for the 313s, and maybe KSA1220AY in place of the 720 just for the extra current capacity and larger package to clip one of these onto (if there is room under the bottom cover):

    [​IMG]

    If you wanted to go completely over the top (as I did) you could enhance the heat sinks for the two loose TO-220s:

    [​IMG]
     

     

    Please register to disable this ad.

  12. davros

    davros AK Subscriber Subscriber

    Messages:
    184
    Location:
    Winston Salem NC
    Thanks for all of the advice.

    So I'm gathering that I should go back to the power supply and replace the 3 2SD313, and the 2SB507? Are they known to be unreliable?

    Also, I have been exceptionally careful with the circuit board stand offs, but I have managed to break one each on power, protection, and equalizer board. Is there a replacement for these?
     
  13. davros

    davros AK Subscriber Subscriber

    Messages:
    184
    Location:
    Winston Salem NC
    Also, Side note... I purchased a cheap ($12) Mega 328 multi-tester. (Made in China)

    It tests all sorts of things, Caps, transistors, diodes, and gives info on each (ESR, forward voltage, ect)

    It seems to test everything, and the caps are right on compared to my fluke multi-meter, but for me all of the numbers are suspect.

    The real value is that it has a graphical display showing the pin-out of transistors. BCE, ECB, and any combination thereof. I checked it against 15 transistors, and it was right every time, forward and reverse.

    Does the same for diodes, showing cathode side.

    Google will show many sources, Amazon is the best bet as they stock them and you can get 2 days shipping.

    Just an FYI for a super cheap bench aid...

    EDIT
    An example of what it displays

    Old BCE
    old BCE.jpg

    New ECB
    new ECB.jpg
     
    Last edited: Jul 29, 2018
    dlucy and Bruno Primas like this.
  14. Watthour

    Watthour Electron Rancher - JS3600

  15. zebulon1

    zebulon1 Getting behind on work. I need help? Subscriber

    Messages:
    4,790
    Location:
    Las Vegas Nevada
    I have a DCA55 pro and several of the cheap eBay/China units. They all work and can be trusted well enough. The readings, when not expected, indicate an issue. Such as a Darlington is indicated but your testing a JFET.
    The DCA pro has a nice feature in testing the Hfe using the software and reads out in a graph when using your shop computer (An older desk top. You need to plug it in, no wifi,). Pretty cool.
     
    dlucy likes this.
  16. davros

    davros AK Subscriber Subscriber

    Messages:
    184
    Location:
    Winston Salem NC
    Yes, those are the ones. I'll add that to whatever my next order is. I can easily see others breaking if i need to remove a board again...
     

     

    Please register to disable this ad.

  17. davros

    davros AK Subscriber Subscriber

    Messages:
    184
    Location:
    Winston Salem NC
    Worked the Flat Amp board today, Recapped and replaced the 2SA725's. Also gave a thorough deoxit Treatment to the pots and switches, then followed up with Deoxit Gold to reprotect the contacts (I don't have faderlube)

    This round of treatment made a tactile improvement to the volume pot, it is much smoother now and easier to turn. After the applying the Deoxit Gold it feels brand new. When I make my next order I may get some Faderlube, but I really don't see the point with how much better it feels now. I haven't tested it yet, as I prefer to give it an hour or so for the Deoxit to evaporate.
    **EDIT** I have tested it, and it is still working great on FM. All scratchiness is gone, and its hard to tell with the cheap speakers I'm using, but the sound is less muffled than before.

    And the Pics

    Flat Amp Before Recap
    Flat amp Before.jpg

    Flat Amp After recap
    Flat amp after recap.jpg
    Original 2SA725
    Original 725.jpg

    New KSA992
    new 992.jpg

    I'll move along to the Tone Amp board tonight, as well as the other switch board for a final round of Deoxit and Gold treatment.

    Then, I'll replace the 2 Transistors on the Power Supply board as was recommended by Watthour.

    I also still need to replace the large Filter Capacitors, I'll do that at some point before I start the Power Amp Board.

    Once that is done, a final test and recording of the readings at the power supply board.

    Final act will be to recap the Power Amp board, replace the 725's, and replace the Bias and zero pots.

    Then adjust DC offset and Bias.

    After that it's reassemble and break it in.
     
    Last edited: Jul 29, 2018
  18. davros

    davros AK Subscriber Subscriber

    Messages:
    184
    Location:
    Winston Salem NC
    Today recapped the Tone Amp Board (AWG-039)

    Got rid of all the Tantalums, and cleaned all the switched and Pots.

    The Pots worked fine before cleaning but were hard to turn. As I cleaned them and they got easier to turn, I started feeling that they had indents and would click when turned (I had no idea).

    The black and brown gunk that came out of the end of the shaft was unreal. The outside of the receiver was brown with nicotine, and I assume that is what was coming out of the pots.

    Tone.jpg tone3.jpg tone4.jpg
     
  19. dlucy

    dlucy dlucy67 (Doug) Subscriber

    Messages:
    1,871
    Location:
    Philadelphia, PA
    I'll share my experience in case you find it valuable. I restored a decent-condition SX-850 a year or two ago, replaced as much as I could, 100% rebuild on the power supply, protection, and equalizer (they mean RIAA EQ for phono playback) boards. Added the diode to protection board to increase relay life.

    It sounded great, operated great... for about a year. Then it stopped working, would not come out of protection after power up. Many trips to the workbench, sometimes I think would work, sometimes it would not. Very frustrating since I'd shotgunned so much of the unit.

    Finally, while watching voltages to/from boards with mini-grabbers, I noticed a spike in power. Digging deeper I found a wire going to the protection board had broken off right at the wriewrapping post. It *looked* like it was connected, but it was just hanging there in space. When the unit was in just the right position, the wire would contact and the circuit would work, but otherwise was open.

    Solution was to reconnect that wire, solder it again... and desolder ALL the wirewrapped posts with extra solder.

    While you're in there, you may want to test each wire connection for looseness or go ahead and solder all the wirewrapped wires.
     
  20. davros

    davros AK Subscriber Subscriber

    Messages:
    184
    Location:
    Winston Salem NC
    Thanks for the tip Doug,

    I had plans to clean the posts with DeOxit out of a squeeze tube, then following up with a little Deoxit Gold to prevent further oxidation. That will obviously not fix a broken wire, but I will check them all as I clean the posts.

    If I solder the wire wrapped posts, should I DeOxit them first, or just solder?
     
    dlucy likes this.

Share This Page