Brought Home A SX-1980 Planning a Restoration.

Discussion in 'Pioneer Audio' started by Fhamre, Sep 29, 2017.

  1. Fhamre

    Fhamre Super Member

    Picked up a nice SX-1980 yesterday. It was only 30 minutes away.
    Well have it on the bench. Was told that both channels worked but no phono.
    Spent a bit of time just reducing the dust level so I could see things.
    From what I can see a less than stellar tech recapped the power supply and changed a few transistors.
    I haven't accessed the back of the board yet to admire his soldering skills buy I can see what he did to the axials.
    I am in no hurry to dive in. I am reading restoration threads and trying to sort out a plan of what needs to be done specifically to the power supply section to make it reliable.The thought of shorting out the outputs keeps me awake at night. I do always use my DBT after any work has been done.
    I did my own baseline assessment of the unit. Confirmed two channel audio and no phono. Tuner works but very touchy and not sure if all the tuner features are working but not too concerned at this point.
    I was able to get the DC offset from over 500mv down to around 10mv on both channels. But only have bias on the right channel . The left reads 0mv and won't adjust.
    I want to focus on the power supply first. Not a circuit whiz/artist. More of a paint by numbers guy.
    I have the service manual.Have restored a lot of gear including at least 3-1250's and a 1080. But its been awhile.
    Would appreciate any advice. Can one disconnect the two driver boards when testing the power supply?
    What bulb wattage would you recommend in the dbt?
    I will keep doing research. I have read about EW's current source modification and Marks LY1 24V recommendation.
    11.JPG
     
    bigx5murf likes this.
  2. zebulon1

    zebulon1 Back repairing the PL's Subscriber

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    Agree. Look at the PS and focus on the back trace side looking for anything that might condemn the board. It would take quite a bit of damage to make me buy the turbo board but depending on your skills the board might fit the bill. I would not hesitate to buy one if needed. Wonderful board and I'm sure it will add value to the set.
    The EQ? Maybe a good Deoxit treatment on the phono switches? Missing supplies?
    The tuner is a little squirrelly. I noticed this on a few I worked. Locking in on a station and getting the centering meter centered is tricky. There is a recent post about the tuner MTF and the experienced poster worked on and it had some really good info.
     
  3. Fhamre

    Fhamre Super Member

    You know I just had a look at the foil side and so far from what I see it looks quite good. Haven't spotted any lifted traces yet. Just the usual dark spots. I suspect once I go it to replace etc I will find some issues.
    Is it good practice to disconnect the driver boards when testing the power supply board?
    Have you made those current source units? Not sure yet on how to build them. I found some bread board. Will likely need the parts but haven't got that far,yet.
     
  4. zebulon1

    zebulon1 Back repairing the PL's Subscriber

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    That's good news.
    Yes disconnect the driver boards.
    The EW current source work a round is very easy using Marks post in the 1980 restoration thread. The leg configuration is important to keep straight depending on the transistors you choose.
     
  5. Fhamre

    Fhamre Super Member

    Easy is not simple! May need to tap you on the shoulder when I get to that point. I saw his diagram and at this point the light hasn't gone on for me. We shall see.
     
  6. zebulon1

    zebulon1 Back repairing the PL's Subscriber

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    I can build two for you if it gets to that.
    Not to keep moving the bar but the install is as important :D
    Just like all of it :dunno: I guess.
    You have some sets under your belt, it will be a good exercise and will stretch your skills.
     
  7. Fhamre

    Fhamre Super Member

    I think I will start by recapping, replace the regulators and any or all transistors I don't like. Plus the relays. Replace the recommended zeners and then see where things are at. Then do the mod.
    Will a 100 watt bulb suffice in the DBT?
    Still have to look at my stock and then do a parts order.
     
  8. zebulon1

    zebulon1 Back repairing the PL's Subscriber

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    100 watt is good with the amps disconnected. You might want to go to something bigger when testing the amps. Like a 150 watt.

    I was thinking about the process wondering if you should look at the amp board that's missing the Idle adjustment?
    It might be something simple like a cold solder or a missed solder from the previous tech?
    It hard to set a prescribed flow to the work because it involves several steps. Like the amp boards. Once opened up you are obligated to complete the board and outputs for a finished product. This might leave the repair in limbo until you can regroup with parts of better info.
    A thought :dunno:
    This restoration should be taken with an open mind and precede only when quality work can be done.
     
  9. Fhamre

    Fhamre Super Member

    Good advice. Just need a few parts. I have the relays but will order the 24V LY1.I will even order the Panasonic relay that Mouser now carries that EW suggests is a bit better than the MY.
    Are the outputs considered disconnected with the just the connectors removed, even though the PS caps wires are connected?I also found I have four 22,000uf 100V PS caps I never used in another project.They were originally to go in a 1250. So they will need a smaller bracket or? To fit properly.
    You don't happen to have a picture of the back of the current source boards by any chance?
     
  10. Fhamre

    Fhamre Super Member

    Also when I get to the driver boards should one plan on pulling the outputs cleaning the old compound off and replacing with new insulators and compound?
    Does anyone know the part number for the insulators?
     
  11. zebulon1

    zebulon1 Back repairing the PL's Subscriber

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    When working the amp boards you should repaste the outputs.
    If your careful you can reuse the mica.
    When using the transistors MTF recommends for the CS's you can connect the leads in rows across the board. He designed it to make it easy to build.
    I don't have an image.
     
  12. Fhamre

    Fhamre Super Member

    Well today my parts came. So I did everything to the power supply board suggested except at this point the current source mod. I will have a go at making the two little boards,tomorrow. Still not quite sure how to make or install them.
    We shall see. Is there a way to test the individual current mod boards before install to ensure they are wired correctly?
    Well at this point I fired up the unit with the driver boards disconnected. Both relays clicked and no bright light.
    Next I will connect the driver boards and take some voltage readings.
     
  13. zebulon1

    zebulon1 Back repairing the PL's Subscriber

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    I might be to late but take the PS supply voltage readings first. Check against the spec's before connecting the amps.
     
  14. Fhamre

    Fhamre Super Member

    I took readings before connecting the amp boards and once connected. They read the same.
    Pin 17 76V,Pin 18 -77V
    Pin 9 33V,Pin 11 -33V
    Pin 8 -29V,pin 12 33V
     
  15. markthefixer

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

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    There are detailed instructions about the current sources, in one of the LOOOONG sx-1980 threads, maybe anderslober? mattsd?? qguy???
    Construction and installation, with pictures.

    IF the pictures are missing, send me links to the defective posts and I'll see what I can do to fix and update them. I really don't have the time to dedicate to the search for those posts.
     
    Last edited: Oct 3, 2017
  16. Fhamre

    Fhamre Super Member

  17. Fhamre

    Fhamre Super Member

    Haven't made the current source boards yet. So far today I just tackled the left amp board. A lot of reflow required. After I put it back together I got the missing bias back. So that's progress.
    I'll do the other side next then see about those cs boards.
     
  18. zebulon1

    zebulon1 Back repairing the PL's Subscriber

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    I've noticed that (Poor wave soldering) on a few of the 1980's and most of the Spec equipment of the late 70's.
    Good find.
     
  19. Fhamre

    Fhamre Super Member

    This 1980 has two slightly different driver boards. Small changes at factory. My guess. Two transistors are different. The two big caps were not glued but raised off the board. Little or no reflow required on the one board.
    I hope to make those CS boards today. May tap you for assistance on how to install.
    Thx
     
  20. Fhamre

    Fhamre Super Member

    That driver board also had a different trimmer a 50K instead of a 150K.I put 50K back in both and they work fine
    My recap ,transistor replacement and reflow of the eq/phono board has fixed my phono. So that's progress.
    My FM is funky on the low end of the scale but decent at holding stations above 100. Was hoping to be able to clean the wipers and variable tuning cap but the top plate appears to be soldered on. Is that correct?
     

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