Help about Jobo ATL1 (possibly ATL2) processor head

Discussion in 'Darkroom Equipment' started by Raphael, Sep 27, 2012.

  1. Raphael

    Raphael Subscriber

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    Hi all,

    I make a call to the ones among you who are (or was) at the same time Jobo ATL1 or ATL2 users and are knowledgeable tinkerers :

    I have some random problems at ATL-1 head power-on, I think it's a reset problem.

    The CPU card is typical of last century technology, and it doesn't bring many problem of reverse engeenering, especially for someone who made his cursus in electrical enginnering in the same last century :wink:

    But one Integrated Circuit give me a big problem, the reference is completely faded out. And I know it's a part of the CPU reset circuit.

    Is any of you has ever seen this circuit board, and have one within eyes reach, or have any schematics, it would be nice if you can tell me what reference is printed on top. I suspect the Jobo ATL2 use the same CPU card with some minor changes, and I don't think the reset circuit should be very different.

    Here is two snapshots of the CPU circuit board. The culprit is circled red on the close up. Given the capacitors/resistors couple connected, I suspect this is a kind of monostable multivibrator circuit, to take down the RST signal the required number of CPU cycle, but any hint would be greatly appreciated.

    In advance, thanks you very much.

    Best regards,

    Raphael

    P9262158r.JPG

    P9262158_close_up.JPG
     
  2. CatLABS

    CatLABS Subscriber

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    Is there any reason you have isolated this IC as the source of the problem?
    I will try to get the schematics to you ASAP.
     
  3. Raphael

    Raphael Subscriber

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    Hello,

    I recognize it's an assumption, but I cleared many other causes, like clumsy lyra IC sockets, for example (changed with new better sockets).
    And if I can fall in electronic lingo, the CPU /RST signal is driven by this IC, through the two open-collector inverter gates of the 7405 you see in the second photo. And another hint to me is the faded away marking : overheating can conduces to such discoloration. And at last, I like to understand what I see : even if the source isn't here, an unmarked IC titillates my brain :wink:

    It will be great ! Thanks you !

    Best regards,

    Raphael
     
  4. Raphael

    Raphael Subscriber

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    Up and an update

    Hi all,

    Thanks to Omer of CatsLab (Krifartida), I got schematics for ATL2 head. But the design is a complete departure from ATL-1, and the reset circuit is totally different.
    However, seeing the schematics put me on the way : the unknown IC is finally a NE556 (dual 555 in a 14 pins DIL package), connected in monostable multivibrator, as I suspected.

    With this hint I was able to make enough tests to exonerate the reset circuit in the problem. It is somewhere else, I haven't found it where for the moment, but I am progressing.

    Thanks again,

    Regards,

    Raphael
     
  5. CatLABS

    CatLABS Subscriber

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    Raphael - one thing i forgot to tell you that you should check is the voltage on the battery on the upper and lower boards. There is a battery that at one point can die, and can cause errors through out. It is hard soldered to the board so you will have to volt meter it there, and perhaps find an alternative replacement if it is bad.
     
  6. Raphael

    Raphael Subscriber

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    Hi Omer,

    Thanks for the information ! In fact, I already done this, is you look at the whole CPU board image above, you will see an empty place at the center : the PCB mounted NiCad battery was here. As it was dead when I got the processor, I unsoldered it and replaced it with a wireless home phone battery, of the same voltage, but with a different form factor, so I sticked it on the PCB other side.

    Maybe it was a part of the problem anyway : the old battery leaked, and tracks and components pins around was obviously corroded. I thorougly cleaned the corroded areas and re-soldered some points.
    For the moment, changing the NE556 eases the things well : the Jobo is up and running again. However, because it's a random problem, I am not sure to have completely solved it.

    Thanks again for your help,

    Best regards,

    Raphael
     
  7. Mike Wilde

    Mike Wilde Member

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    You are on the right track. I would also change out any old electrolytics.

    I find swapping old ones for new ones clears up an awful lot of flaky problems with 20-30 year old electronic gear.

    It has brought my Fujimoto CP31 roller processor and wash dry unit back from the dead, as well as a few different Vivitar timers.
    The other thing Vivitars have is a zerner diode and resistor voltage reference. The resistor burns up, and all stops. I replace this resistor and zener with a regulator, and all is happy again.
     
  8. mike torrisdale

    mike torrisdale Member

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    Hi,
    Sorry to trouble you after all this time but I desperately need help.
    have a ATL-1 in need of a new nicad battery - which are impossible to find. I noticed from your thread that you have managed to source a replacement. I would be grateful if you could let me know how you managed this especially as the battery has 3 connections.
    Any help would be gratefully received.
    many thanks
    Mike