Qrx9001 f2624 board swap

Discussion in 'Exclusively Sansui' started by Justcuz, May 12, 2018.

  1. Justcuz

    Justcuz AK Subscriber Subscriber

    Messages:
    61
    Location:
    East tenessee
    I have the hood off a dead 9001 comparing it side by side to a restored machine.Both are silver chassis one is missing serial numbers so I can't give production dates. I see f2634 boards are a little different.My dead 9001 was stored since 1982 and stays in protection.If I pull f2624 boards protection relay engages.Would I be safe swapping good boards into bad machine?I'm not a tech.Most these topics have probably been covered and I've probably read them but this 9001 has a overwhelming amount of info to take in.I'm just trying to do a quick safe trouble shot to bring this beast to life.I have 3 9001 2 silver chassis 1 gold and all 3 have there differences.I'm nervous about putting my rebuilt f2624 boards into the unknown.lol.Any input would be appreciated.
     

     

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  2. tnsilver

    tnsilver AK Subscriber Subscriber

    Messages:
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    Can you check a transistor? If so, verify all the output transistors are intact and no blown fuses on board. When all clear, use a DBT to power up the suspect unit with the good boards.
     
  3. Justcuz

    Justcuz AK Subscriber Subscriber

    Messages:
    61
    Location:
    East tenessee
    Outputs are good no blown fuses or swollen or leaky caps.No burn marks anywhere.Two 180ohm fuseistors seem to have lost there colors other than that all is clean and pretty.I don't have the DBT to bring it up slowly.When I purchased it from original owner he pulled it out of storage he plugged it in to test it so it was already rudly awakend when I got it.My compatible good boards are in a completely rebuilt machine that sounds incredible.My gold chassis boards are also rebuilt just different style.
     
  4. tnsilver

    tnsilver AK Subscriber Subscriber

    Messages:
    3,314
    Location:
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    A DBT is not a variac. It doesn't slow down the firing up, it just limits the current to the device, so an otherwise catastrophic short or current surge is absorbed by the light bulb, which goes indicatively bright. It stands for Dim Bulb Tester and you can build one in 10 minutes for less than 10 bucks. Don't do squat without it.

    EDIT: Its so rudimentary. Here's one from a recent thread:

    [​IMG]
     
    Last edited: May 12, 2018
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  5. Justcuz

    Justcuz AK Subscriber Subscriber

    Messages:
    61
    Location:
    East tenessee
    That's solid advice I appreciate it.I'm just getting back into audio after years of car building and somehow have picked the 9001 to learn on.I would like to set up a functional bench to work from but I have a move coming for work and I haven't been able to carry much stuff while transitioning.It does drive me crazy having a dead piece in the collection and I'm so cheap I would rather fix it myself vs paying for it.That's how I got started with cars I refused to pay someone to do something I could with some effort.Money the great motivator.lol.Thanks again for your wisdom.Good thing I have lots of sansui to keep my ears busy while I'm learning.
     
  6. sKiZo

    sKiZo Hates received: 8641 Subscriber

    The F2634 boards saw a major revision about halfway thru production, but all the x001 boards are interchangeable. Last I heard, the x0x0db boards are not compatible with the x001 machines.

    One thing you DO want to do after changing the boards is verify the bias and offset as those can vary from machine to machine. Be VERY careful adjusting those pots as the slightest tweak can put you way out of range.

    You couldn't have picked a more complicated receiver to get your feet wet on, could you? Restoring mine was ... interesting ... in a Chinese sort of way, but I'd rather slam my (insert body part here) in a drawer repeatedly than go thru that again ... <G>
     

     

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  7. LBPete

    LBPete Rolling Along Subscriber

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    First, the 9001 is too complected and expensive as a learner mule. It's F-2624 used fuse resistors and suffers from them failing just like the other receivers of that era that use this board. That would be the first place to start.

    Swapping boards can be a good shortcut but its not without hazards. If your 9001 has shorted outputs, they could take out the driver transistors on your substitute board.

    - Pete
     
  8. tnsilver

    tnsilver AK Subscriber Subscriber

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    Location:
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    Interesting, what did you hear - any details?

    A quick diff on the SM's of both shows very minor semi-conductor differences:

    (9090DB vs. QRX9001)

    TR01-TR04 (diff. pairs) 2SC1400 vs 2SC1708 - both replaceable with modern KSC1845 - it makes no difference
    TR09 - TR10 Older F2624 driver amps use 2SC984 Hitachi transistors, later use STV-3H stabistor diodes - the two versions of the driver amp are interchangable

    I think they are fully compatible. I haven't dug deeper but the F2624 driver amp seems kind of universal, isn't it? There's lesser gain specs on the driver transistors
    of the 8080DB driver amp (model "B" as the SM calls it) but otherwise, pretty much the same - right?

    A funny thing with the trimmers on the 2SC984 vs. STV-3H boards. One yields more bias current with more resistance, the other less bias current with more resistance.
    Unfortunately I don't remember which is which. :dunno:
     
  9. sKiZo

    sKiZo Hates received: 8641 Subscriber

    Did some digging here ... come to find out, it was LBPete that I remembered had doubts, but that was a while back ...

    http://audiokarma.org/forums/index....90-driver-board-r.795125/page-2#post-11004894

    And yah - like he said, the fuse resistors are prone to failure and will open the circuit when they do. Those lil guys run HOT and will crack and turn to dust over time. I replaced all mine with equal value metal film, and was careful to set them high on the boards for max air circulation around them.

    In case anyone's wondering what we mean by complicated, here's what one will look like during a "simple" switch cleaning ... :yikes:

    [​IMG]
     
  10. kevzep

    kevzep Its all about the Music Subscriber

    And when the front comes off like that, you are in danger of losing the tuning dial string!! Lose that and you've got a real headache on your hands......

    I have a QRX9001 coming in for a restore in a few weeks, it will be my second one.........not a beginner job!!
     
  11. sKiZo

    sKiZo Hates received: 8641 Subscriber

    Little trick I learned from Trnsfmr (rest his iron) ...

    [​IMG]

    The ends heading for the front panel can be taped to the side wall to keep tension on them, and the rest can be looped back and taped to the back panel during surgery. Green tape leaves no residue.
     
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  12. kevzep

    kevzep Its all about the Music Subscriber

    Yah, thats what I do too, just gotta make sure you get it right and it doesn't come off.... RIP Jim...
     
  13. Justcuz

    Justcuz AK Subscriber Subscriber

    Messages:
    61
    Location:
    East tenessee
    I agree with Pete,not the receiver for a rookie for sure.I did pick a kenwood kr2600 for free to practice on just no time to practice.While I have your attention on the qrx9001 my gold chassis has had the pass thru pinning done when its playing in 4 channel mode I have 4 channels playing in hall mode when I switch to surround qs an sq I lose left channel cd4 mode it returns and when its at idle I here a discharge or static type noise not adjustable with volume.It seem to stop after idle for a few minutes.It has had caps and resistors changed in pre power and f2624 boards also in 4 channel boards.It seems to have unequal balance on low end of volume dial then is balanced fine after at level one and higher.When the left channel drops it's not completely gone but faint.I suspect a bad joint in pinning process but hoping its more simple.I tried to compare the wiring of the switches themselves but all three units are different on how the wires are routed and connected.I'm using my unmolested silver chassis for reference.I bought 2 9001 and one is perfect and sounds incredible and the other has the symptoms described.Two different techs done the work by the way pinning procedure was done.I would like to send it out and get it fixed but I have one totally dead that needs to see the Dr.first.Thanks you all for your input.Don't you just love a good qrx problem to figure out.
     

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