SX1980 Voltage Regulator / current source question

Discussion in 'Pioneer Audio' started by Jon1982, Dec 2, 2017.

  1. kevzep

    kevzep Its all about the Music Subscriber

    I don't know why you are trying to fumble around getting the original circuit going, it is far more efficient and a much better solution to make the Echowars current source's and install them, they are so easy to build and install.
    There's a lot of information about this in the forum here, and people to guide you.
     

     

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  2. rcs16

    rcs16 Super Member

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    Do you want me to design a pcb for this CC source, it is a very easy design, would take about a few hours to make it. More time to figure out the dimensions. :)
     
  3. markthefixer

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

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    I DID post a perfboard (3 hole per pad, 6 pads in a row, 0.400 wide and 0.700 long) version of the circuit
    AND thoroughly, exhaustively documented It's construction, with parts list.
    THEN I documented it's installation. Probably an an Anderslober sx-1980 thread.
     
  4. kevzep

    kevzep Its all about the Music Subscriber

    Here you go, couldn't be easier...
    current.jpeg
     
  5. kevzep

    kevzep Its all about the Music Subscriber

    And parts list.. you might have to sub the transistors on that list because I don't think the ZTX is available any more.. upload_2017-5-15_15-10-6.png
     
  6. markthefixer

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

    Messages:
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    And what I did was to leave the resistor and LED wires uncut on the corners, for electrical connections and for mounting considerations.

    current_regulator_mtf.jpg
    ----------------------------------

    Two resistors, two zener diodes and a JFet are removed from each regulator circuit, they are unneeded and their holes are used to mount the current sources.

    In the pictures, the positive polarity leads go into at least one green hole
    the negative polarity leads go into at least one yellow hole
    the white marked holes are isolated and can be used for mounting, as long as
    you don't put a positive and a negative into the same foil's conjoined holes.


    Positive Regulator Current Source placement
    positive_regulator position.JPG
    ---------------------------------

    Negative Regulator Current Source placement
    negative_regulator_position.JPG
     

     

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  7. Jon1982

    Jon1982 Member

    Messages:
    63
    Thanks for the info folks and I've got the parts on order.

    In the meantime I've been trying to work out what has upset the low voltage supply.

    I change Q201, 202, 203 and the 6V zener - but I notice the source select / speaker select lamps on the front of the unit are dim.

    So I decide to disconnect the +13.5V outputs which go to the tuner, meter amp and APC board.

    Hey presto the lamps light up correctly and I check the voltages which are now very close to spec.

    So I reconnect the APC & Meter amp feeds and we're still okay.

    I then reconnect the tuner feed and Q201 shorts out again.

    So, something has gone bad on the tuner, or maybe the problem only manifests when a certain load is reached.. I measure the resistance to ground on the feed to the tuner (that is, pin 7 on the tuner PCB) and I see 100 ohms. So, that would only be 135mA draw which sounds pretty nominal to me?

    There would seem to be a common theme with me getting the output voltages from the board where they should be, but then problems occurring when I'm reconnecting the loads. Am I missing something?

    Q201,202 2SC945 was sub'd with KSC945 which looks to be the same spec with different pinout.

    I am going to throw this thing in the river soon or perhaps attach a handle to it and use it for weight training.
     
  8. zebulon1

    zebulon1 Getting behind on work. I need help? Subscriber

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    You seem on top of it but you still are missing the big picture.
    I learned this from MTF.
    And. I should be the one to talk with a Spec causing me issues but I do know the 1980 PS in that you have to replace all the silicon when a PS failure occurred.
    The whole shooting match or you will chase your tail. The good regulators will be stressed when the bad give way. The new CS workaround needs to be built and installed. New everything and it will work.
    That PS has to be fresh when powered on after a repair. Trust me.
    The TurboX board is the cats ass. Worth every penny. An option and I believe, a value added upgrade to the Masterpiece.
     
  9. Jon1982

    Jon1982 Member

    Messages:
    63
    Thanks zebulon. I was wondering if it is possible for semi's to test OK on a DMM but still actually be faulty. I can certainly have a go at changing all semis in one hit.

    I am considering the board upgrade but I'm put off by criminally high import duties, (and also that I hate being beaten!) perhaps I could get one shipped over to me next time I'm in Vegas..
     
  10. zebulon1

    zebulon1 Getting behind on work. I need help? Subscriber

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    I'll help out how ever I can. ;)

    Replace the FET's with the EW mod and Marks instructions.
    Rebuild the board with new silicon with the addition of the Service letter:
    It should be good.

    Capture 1002.PNG
     
  11. Jon1982

    Jon1982 Member

    Messages:
    63
    While waiting on parts for the current source I've been messing with the +13.5V - replaced all the transistors in that area and get the correct voltage at no load (well, marginally over). I reconnect the tuner feed, this time with my DMM connected ready. Initially voltage is correct but rapidly decays. I quickly switch off to avoid damage.

    I decide to connect a 100 ohm resistor as a dummy load. Voltage is okay at around 13.5V for around 30 seconds, then suddenly jumps up to 14+V, then violently to zero and back a few times, presumably as something goes into its death throes.. at least it looks like the tuner board is off the hook.

    So, is there anything else that could be doing this? I see there is a link across to the +80V regulator but I don't know what this is for. I don't want to muck about doing the current source mod if I've got another unrelated issue that I can't solve. Thinking of just giving up now and getting the all singing all dancing replacement board.

    Q201, 202, 204 were subbed for KSC945

    Q203 & Q205 were subbed for on semi D44H11G.

    Original failure mode was R202, Q201, Q202 & D207 toast.

    TIA
     
    Last edited: Jan 3, 2018

     

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  12. Jon1982

    Jon1982 Member

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    63
    Anyone any more suggestions for me before I gives up?

    Any common componentry that might cause both the -80V and +13.5V to die? That is, voltage fine under no load, but once load connected, transistor fail?

    Does the current source on the +80V also kick start the +13.5V? Thus could a problem there be killing the 13.5V?

    The +80V has never failed and I've never touched that, save to replace the failure prone zener diode.

    My input voltages are slightly high but only by a couple of volts, i.e. 110V vs 106V spec. My mains voltage is slightly high at 247V versus 240V spec. (yep the voltage selector is set correctly... was set to 220V when I bought the bloody thing)

    I've just been diagnosed with a case of shingles, bit of an old person disease, but I'm only 35... apparenty STRESS can be a trigger, probably SX-1980 related... :mad:
     
  13. Jon1982

    Jon1982 Member

    Messages:
    63
    Anyone have any more suggestions for me now I've sufficienty recuperated?

    Was thinking of whipping the feeds to the PSU board out, and checking the AC voltages.
     
  14. Jon1982

    Jon1982 Member

    Messages:
    63
    SX1980 Guru needed!

    Had another delve around. Only Q201 failed this time (failed short). Q202, 203, D207 all check OK
    It occurs to me that there's only so much that can possibly be doing this.

    Would I be right in saying that Q201 gets its base voltage from the +80V, dropped down by R201?

    I'm wondering if a problem here is destroying Q201 and then causing a cascade fault.

    The +80V has never failed but is slightly high (say 81-82V)

    I'm not trying to bodge the board or cut corners but I'll be miffed if I do the CCS mod and the thing is still not right.

    Thanks in advance, you lovely people.
     
  15. kevzep

    kevzep Its all about the Music Subscriber

    You need to do the mods to the board for future proofing it against certain failure.

    Have you replaced ALL the silicon on the board?

    Have you checked all those low value large resistors, and I mean all of them, the ones on the board I worked on were way out of spec, gone high resistance.
     
  16. rcs16

    rcs16 Super Member

    Messages:
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    Location:
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    This is one of the more difficult units to work on esp for a hobbyist. I have never even worked on one so listen to experience, it will hopefully save you any more stress.
    I agree with kevzep and his experience, I'd go over everything and maybe just replace them while you are at it.
    Make those CC source boards!! Maybe you have other problems but using the CC ckt will help you towards a proven more reliable solution.
    In my opinion, it is best to isolate the PS from the loads get it going properly first, even test with dummy loads before hooking it back up.
    Do not worry about slight differences is document voltages and what you are reading, there are at least %5 tolerances
    Did you figure out the pinout difference between ksc945 and ksc945c, always good to reference the datasheets for ksc945 and NEC 2sc945

    Good Luck
     

     

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  17. kevzep

    kevzep Its all about the Music Subscriber

    What did you replace that D207 with? Should be a 1N5234B Zener.
     
  18. Jon1982

    Jon1982 Member

    Messages:
    63
    Thanks for replies guys. I was just trying to gain some hope that it might fix all the ills with the board, what with the interplay between the +80V and +13.5V, which I don't fully understand.

    D207 replaced with RS part 813-3940

    Yes I noticed different pinouts on the KSC945. I ought to have ordered the KSC945C, by the looks of it, as a drop-in replacement for the 2SC945. The SX-1980 has little symbols on the PCB to denote transistor type and orientation, and I've been relying on that being right, I know Mark the fixer will tell me off for that!

    You are right about this unit being a sod and I'm somewhat out of my depth - but I'm hoping it'll be all the more satisfying when I finally sort it! What I lack in experience, I hopefully make up for in tenacity!!:bigok:

    I will do the CCS mod since I now have the bits and will double check resistors etc. as advised, I will report back.
     
  19. rcs16

    rcs16 Super Member

    Messages:
    3,632
    Location:
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    I suggest to test the CCS ckt on its own before you install it
     
  20. Jon1982

    Jon1982 Member

    Messages:
    63
    I took up your suggestion.

    And saw that I have made a daft, albeit slightly forgiveable, mistake :)

    If I attach the circuit diagram with a little addition to make things a bit more obvious to fellow dumbasses, you can probably guess what I'd done wrong! currentsource.jpeg
     

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