Project: SX-1250

Discussion in 'Pioneer Audio' started by Super Noob, May 27, 2018.

  1. Super Noob

    Super Noob Member

    Messages:
    91
    The sickness continues. Getting into a 1250 that I picked up recently. 2nd owner had it for 25 years = ~1993. Here is what I found = looks as if it has never been opened. All the lamps look original and were working.
    [​IMG]

    Need of a good cleaning - working through that now.
    [​IMG]

    It adjusts outs very well:

    Main Rails:
    [​IMG] [​IMG] [​IMG]

    Bias - Each Channel (read a bunch about setting anywhere from 70mV to 100mV). I elected 80mV.
    [​IMG] [​IMG]

    DC Offset - Both Channels:
    [​IMG] [​IMG]

    All I can say am pretty impressed = 40+ years later and she was not really far off with original components.

    Maybe I should leave well enough alone, but I going to do all the caps, trimmers, + relays. Here is the lights (all changed). Four Dials & Nine Indicator Lights. The 1250 looks to be very easy to work on compared the other units I have completed - plenty of room.

    [​IMG]

    Am finishing up the cap list (based off of MTF / Mattsd posts)... but I don't think I am going to wholesale the transistors. I will share in .xls format shortly.

    There are a few folks here that have done more than a few SX-1250 (and are miles ahead in experience on this unit) = what transistors do you all recommend being replaced for increased reliability or improved sonic performance. I might just ensure I have them all in stock and place the order later today (minus the main outputs).

    Most threads are centered around a wholesale rebuild = transistors and diodes. Thanks in advance for sharing your thoughts.
     
    Last edited: May 27, 2018
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  2. kevzep

    kevzep Its all about the Music Subscriber

    I'd do the transistors and diodes in those BOM lists, so many of the smaller TO92's are going noisy and leaky these days because of age, this way you'll never need to open it again in your lifetime.
    They don't cost much, and you're in there anyway.
    There is the "romance" of originality, and sonic signature that some people seem to attribute to the transistors which Pioneer used....Once you are past that and think about it, you'll want to replace them....
     
  3. Super Noob

    Super Noob Member

    Messages:
    91
    Kevzep = thanks.

    Hard to argue with that logic.
     
  4. kevzep

    kevzep Its all about the Music Subscriber

    No problem..... Another thing I am always weary of in Pioneers, is the wire wraps they use, so when you pull the EQ and flat amp board out, you are going to be de-soldering, then putting the components in, then soldering, you'll be swinging those boards back and forth, this can stress those wire wraps out and sometimes the wire can snap off....So just be careful moving those boards around, minimal movements.

    I have a wire wrap tool, I got it after I seemed to be getting a lot of Pioneers to work on.....makes things easier to put back to "factory". Soldering onto those wrap terminals is not recommended.
     
  5. kevzep

    kevzep Its all about the Music Subscriber

    Oh and by the way, that is a very nice looking SX1250 too, unmolested!! A virgin!!
    You are very lucky!!
    The one I am working on is fairly beaten up....but I'll get it back on track...
     
  6. Super Noob

    Super Noob Member

    Messages:
    91
    Thanks Kevzep.... I have fully recapped STA-2100, STA-2000, SX-850, SX-750, 2325, SA-800 = all with careful attention to the heat-sink triple diodes, never removing wire wraps, and all completed with much luck and never having to un-wire a board. This unit should be a walk in the park comparatively; however, I will heed your advice and be very careful and minimize board swinging. :biggrin:
     

     

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  7. KingBubba

    KingBubba "Too Much Stuff"

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    You can desolder the wrap post from the board, making it much easier to deal with. Unwrapping and rewrapping the posts requires a new post and fresh wire. The sharp corners on the post are dulled by the original wrapping. Many times there is not enough slack on the wire to do a re-wrap and a stretch of new wire will need to be tacked on the old wire. Un-soldering the posts from the board is the best all around method. The nice thing about the 1250 is the modular construction. For the flat amp, take great care in cleaning the filter switches. Clean with Deoxit, lube with Caig Fader and seal with Caig shield. Because they are such troublesome switches, both in removing the flat amp and the fact that that just Deoxiting does not last. The Shield helps you with having to repeat the whole process again in a year. Have fun with your new Monster.
     
  8. Super Noob

    Super Noob Member

    Messages:
    91
    KingBubba = Nice Post

    Never thought about de-soldering the wrapped pins. It is not too bad to take care and support loose boards, then I rotate the entire assembly - not the board. Very little noise in the switches and knobs. I use Deoxit and Fader lube = never experimented with shield; I will have to try. Am about 3 hours south of you on the left coast = getting some rain up there?
     
    Last edited: May 27, 2018
  9. onwardjames

    onwardjames Hoardimus Maximus Subscriber

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    I love being a voyeur on threads like this. Good luck, sir!
     
  10. kevzep

    kevzep Its all about the Music Subscriber

    All good, you'll be fine with all those units under your belt, and yes, the layout is easy to work with.

    Sometimes you can unsolder the post, but not always....but as long as caution is used, you'll be fine.

    I've rewrapped wire before and seems tight and secure, I think you only get one chance though because as stated the wires will dull the edge on the post....
    Its a matter of assessing and acting as necessary.

    Yeah always use SN5 to shield...a lot of people don't, as deoxit DN5 will do its job, but when it dries out it leaves the nice new contact surface to oxidise again...
     
  11. PabloX

    PabloX AK Subscriber Subscriber

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    It's great to see 1250s being preserved.
     

     

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  12. zebulon1

    zebulon1 Getting behind on work. I need help? Subscriber

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    My advice is to completely rebuild the stabilizer board (transistors, diodes/zeners and caps) as I mentioned in a current 1250 thread. The small signal transistors on the rest of the boards, the problematic ones, replace. The rest can be left alone. Of course it up to you on how far you want to take the set.
     
  13. KingBubba

    KingBubba "Too Much Stuff"

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    We have been putting up with sporadic drizzles, no wind or anything brusk. I hope it stays that way.
     
  14. Super Noob

    Super Noob Member

    Messages:
    91
    Here is the first pass... open for use. The mouser cart is ready for execution.

    List was started by MattSD & MTF (credit to those folks).

    I use WIMA for caps under 2.2uF. It appears that much is thought of the UKL for signal path electros. Am thinking about changing these to "KA" series. Anyways... I think I will create a second tab with KA in place of UKL. Am curious to anyone's thought on this route.

    https://drive.google.com/open?id=1o-A55kI6F1Ot7Bz2uAdcZtRAnBzvMar7
    (two tabs)
     
    Last edited: May 28, 2018
  15. rcs16

    rcs16 Super Member

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    Good job. Always good to have options. since UKL vs film can add up to a fair bit more coin.
     
  16. slow_jazz

    slow_jazz Lunatic Member

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    Congrats and good luck with your resto..
     

     

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  17. kevzep

    kevzep Its all about the Music Subscriber

    Good work on the spreadsheet!!
     
  18. kevzep

    kevzep Its all about the Music Subscriber

    Worth it though, made a massive difference on my SX1010...
     
  19. WE6C

    WE6C Well-Known Member

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    Location:
    Colfax, Northern California
    Kevzep, Do you recommend the "shield" after using the "fader" on the switches?
    Thanks, Bob
     
  20. rcs16

    rcs16 Super Member

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    3,586
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