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  1. #21
    tim_walls's Avatar
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    Quote Originally Posted by arigram View Post
    So, the chip and capacitors are ok then?
    What should I look for?
    The rest of the circuit looks fine (for a layman).
    If the relay turns on/off as you adjust the target temperature setting, the chances are high that the circuit is working (you would expect the point at which the relay flips to be around the current ambient temperature - i.e. if the water is currently at 21 celcius, you'd expect that the relay would flip as you move the target temperature setting past 21C.)


    For what it's worth, the chip you identified - a 7485 - is a 4-bit comparator; this is, it compares two digital numbers and outputs an indication of which is higher (or if they are equal.) It very likely is a part of the thermostat circuit, therefore (the output of the comparator would be what turns the relay on/off to turn the heater on when the sensed temperature is less than the set temperature.) If the relay isn't behaving as described above, then this chip is therefore implicated; it sounds more likely though that it's all working as intended from what you describe.


    In which case, if the relay is operating correctly, that more or less leaves the heating element, which is sad - if the element is buggered you're going to need Jobo to provide the replacement.

    As far as I know (I have a CPE rather than a CPP, but I assume the element is the same) the element is of the nichrome-heating-wire-inside-a-ceramic-pipe variety. The two main failure modes are the heating element breaking, or the ceramic cracking.

    Presumably, the ceramic hasn't cracked. If it had, the earth-leakage circuit breaker (which you do use, I hope) would trip as soon as the heating element turns on. A cracked element means the water in the bath is connected to the mains when the heater turns on (if the appliance wasn't connected to earth for some reason, this would make it a real hazard) - an RCD/GFCI breaker will detect this as earth leakage and trip.

    If the wire has just broken, there's not a lot you can do other than replace the element though :-(.


    There is some good news though:
    A fault with the heating element is easy to diagnose for anyone with a multimeter. With the element disconnected, use the resistance checker to check continuity through the element (there should be a high resistance, but not open circuit.)

    To check for a crack in the ceramic, fill the bath with water and then check resistance from the heater element to the outer layer (which is normally earthed.) It should be open circuit if the ceramic isn't cracked.

    There may be some other components in the heater element circuit other than the relay and the element itself; there may be a separate fuse for the heating element, there may also be a thermal fuse which will blow if the thing has ever overheated (e.g. by being operated with no water in the bath,) it could even just be a loose wire. So don't panic yet .
    Another day goes under; a little bourbon will take the strain...

  2. #22
    tim_walls's Avatar
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    Oh, incidentally, in the unlikely event that the 7485 chip is buggered, it costs less than 50 pence and is readily available - I probably even have one in my parts tray I can send you if you need one in case it's tricky to get hold of in Crete.
    Another day goes under; a little bourbon will take the strain...

  3. #23
    arigram's Avatar
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    I just got word that the technician is on vacation.
    I also got an email from the German technician with his address to send the jobo too.
    I think I might wait a bit, to finish a couple photoshoots I have planned and either try the local guy or send it over to Germany. Since its just the heating, it can wait.

    Thank you Tim for all the detailed description.
    Are you an electronics professional? Because it looks like you're having fun fiddling with it.
    aristotelis grammatikakis
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  4. #24
    tim_walls's Avatar
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    Quote Originally Posted by arigram View Post
    Thank you Tim for all the detailed description.
    Are you an electronics professional? Because it looks like you're having fun fiddling with it.
    Ha, no, just a hobbyist - although I used to write embedded software back in the day when programming was a skill and understanding the hardware was considered an advantage (just throwing a faster processor or more memory at your bad code is not an option when your processor has a princely 256 bytes of internal RAM and you've run out of IO pins to attach any more...)

    I still keep my hand in by designing/building microcontroller boards and keep old computers (I have a DEC PDP-11 which has sadly been in storage too long waiting for me to move into a bigger house...)


    The problems people keeping older computers and electronics up and running face are not dissimilar from the problems people face keeping 'old' photographic techniques alive; parts are hard to find if not unobtainium, information is locked up in company research libraries if it hasn't been lost completely, and the general knowledge just seems to be rarer and rarer in an age where 'repair' means 'replace entire boards until the thing seems to work again'. Thank God for the Internet - APUG and its equivalents are a godsend for making sure the information that is out there doesn't get lost forever.

    (Err, sorry, started rambling there...)
    Another day goes under; a little bourbon will take the strain...

  5. #25
    Steve Smith's Avatar
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    Further to my previous post: The processor I have in the shed is not a CPP-2 but is a CPE-2 Plus. However, I assume that the heater and its controller are similar, if not identical.
    If you want any parts from it you are welcome to them.

    Steve.
    "People who say things won't work are a dime a dozen. People who figure out how to make things work are worth a fortune" - Dave Rat.

  6. #26

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    CPP-2 units have two styles of circuit boards, old style – new style, this is the new style. The chip is IC53 on schematics and is a 74LS85N. The chip interfaces the output of the BCD switch (the rotary switch for tenths digital, "binary coded decimal") into the circuits that regulate temperature. From the corrosion in your picture very likely this could be your problem. Inexpensive part but you need a tech that can remove the chip without destroying the circuit board, this type of corrosion can weaken the lands on the circuit board. It should be repairable.

    Best regards,

    Ed

  7. #27

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    Refreshing an old thread... Sorry

    Hi Ari,

    Have you solved your CPP-2 heating problem, since July ?

    I run yesterday in the same problem, on a Jobo ATL-1 (which use the CPP-2 as base) before I discovered that the "canceled-hidden-secret" thermal switch went off. It take long minute between the moment when I find the clue on the Net, and the moment I actually discovered the switch...
    Of course, I presume you had checked that a long time ago.

    Otherwise, as a electric engineer from my student days, I confirm all the things already said, your problem came certainly from the corroded printed circuit board around the 74LS85 IC. This binary comparator checks the consigned temperature against the real bath temperature (binary converted) and order the heating element goes on or off, IMHO.

    It's a pity that buttons and human interfaces on these Jobo processor are not really waterproof, and at reach of any corrosive chemical spilled. On my side,
    I discovered too traces of chemicals in the electronic head of my ATL-1, but hopefully without impact on PCBs.

    BTW, I changed the exhausted Ni-Cd cell used for processing programs backup by a new one (in fact a more current, adapted), and the thing seems to working well.

    I am interested of any experience on Jobo fixing and tinkering ;-)

    Regards,

    Raphael

  8. #28
    ic-racer's Avatar
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    Just saw this thread. If you are still working on this, you could try cleaning around the IC chip or just replacing it. Here is the technique I use: http://www.largeformatphotography.in...7&postcount=59

  9. #29
    arigram's Avatar
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    I haven't done anything the the Jobo, truth be told.
    I was swept into an abyss of personal matters and photography has been put on hold and while I plan to send the machine to Germany every week, I keep postponing it.

    Raphael, if you are right, I only need to replace the chips and this is a job that can be done here by a technician and won't need to send it away. Are you sure about it?
    aristotelis grammatikakis
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    no digital additives and shit




  10. #30

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    Hello Ari,

    Quote Originally Posted by arigram View Post
    Raphael, if you are right, I only need to replace the chips and this is a job that can be done here by a technician and won't need to send it away. Are you sure about it?
    Sorry, I can't be sure of anything, without the actual schematic, my assertions are just guesses based on the pictures and IC reference.

    However, if the technician does a correct job, it won't harm to clean and check this part of your Jobo, given the pictures you'd showed us.
    Maybe, it is not the Integrated circuit itself, as said sooner, it's rather hard to die, but certainly the Printed Circuit Board tracks that connect it. Are the PCB tracks look corroded around the 74LS85 chip ? Have you tried to clean gently it and around it ? With isopropyl alcohol, by example. After unplugged it from the outlet, of course !

    If you know how to use a multimeter, you can check tracks continuity yourself, starting from the chip pins using the multimeter "ohmmeter" setting. Sorry if I seems to talk chinese, here...

    If you are used to work with electricity, with a multimeter, you can even check if the chip does its job, with checking its output going up (about 5v) or down (about 0v)...

    The technician can do this for you, an can be a good option. Of course, if he will take big bucks for the work, or if your Jobo is still under warranty, may be the return at Jobo AG will be preferable.

    You writed sooner, you heard relay clicking when you rotated the temperature knobs, but was water bath filled ? Because, if you power up your CPP-2 without water, the overwarm of heating element will trigger automatically the "thermal protection switch" off, and the Jobo don't warms water (but all LEDs are still lit) until it's armed on again.

    I discovered it a few day ago, when I powered up my ATL-1 without water in it, for testing my CPU battery mod, the thermal protection switch in the CPP2 part goes off, cutting the heating element power, maybe in the 30 seconds...

    Don't hesitate to PM me if you have any questions or need help I can bring to you.

    Regards,

    Raphael

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