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Thread: Jobo Resistor

  1. #1
    Thiago Lara's Avatar
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    Jobo Resistor

    Hi, Apugers!

    Bought this CPE-2 on fleaBay some months ago to backup my CPA-2. It came with the motor somehow slow... you can see in the video below:

    http://www.youtube.com/watch?v=kJvExXiq3jY

    I'm in Brazil, and it came from US. So just the shipping to receive it was almost the same value of the processor, sending it back would only make me loose more money, so was not an option. Didn't bother to contact the seller, since the guy basically sent me his trash, it's hard to believe that he didn't knew the processor was defective. After months trying to find someone to service it here, I decided to try it myself. Found a blinking toasted resistor in the control board, it blinks when the motor inverts:



    Here's a picture of the board of my processor:

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    The problem is that I can't identify the resistor by the stripes, I think the former owner has insisted in using it this way during some time, the thing is really toasted, it's gray:

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    I find the picture below on the internet, this guy has changed the whole board in order to keep the high voltage on the lower speed setting and keep the torque high... another thing, but there's a picture of the original board there... unfortunately it's black and white.



    here:http://www.tech-diy.com/Photography/...oller/jobo.htm

    Would some lovable owner of a CPE-2 here make me the huge favor of opening the panel of the processor to identify the resistor, so I can try to find one to replace it? This things are identified by the number of the stripes and it's colors, I'm informing myself about it as I research a solution for this machine, I know nothing on electronics, so a picture would be great. But I understand that people here doesn't have digital cameras – I've actually thinking on selling all my digital crap everyday since I started with film – so if a picture it's not possible just a identification on the colors of the stripes on it will be fine as well.

    And since I'm already asking, I would love to know more about resistors and this specific problem. What could have caused it? I read thats usually caused by an overload, but what can be the cause for this overload? A subtle variation in the power? Plugin a 110v machine in a 220v wall socket? I'm wondering if it's something external or another component in the machine which may be the real cause for this toasted resistor. What do you think?

    Thank you very much,

    Thiago Lara.

  2. #2
    ic-racer's Avatar
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    This is a guess based on the pictures, Brown, Black, Orange, Gold = 10k 5% Carbon film resistor.

    There are others on this forum (like Gregg Blank) that can give an exact answer.

  3. #3
    ath
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    Most probably the resistor gets overloaded because something else is wrong. Changing the resistor alone will probably not cure the problem. Maybe the motor is the problem.
    You might want to contact the Jobo Analog service in Germany and ask for a replacement board or they might give you the schematic and someone with electronic skills repairs your board.
    Regards,
    Andreas

  4. #4
    Diapositivo's Avatar
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    I have the Jobo CPP-2 Service Manual.

    I don't know which are the differences between CPP-2 and CPA-2 but it can be of help. Plenty of electric schemes.

    I tried to attach it to this post but the operation does not work.

    I'll try later, or I can send it to anybody requesting it if they send me their email via private message.

    Fabrizio
    Fabrizio Ruggeri fine art photography site: http://fabrizio-ruggeri.artistwebsites.com
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  5. #5
    polyglot's Avatar
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    CPE-2 is very different from a CPP-2, otherwise I'd go look in mine for you. You could PM hoffy, I know he's got one and he's had it apart for repairs.

  6. #6
    EdoNork's Avatar
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    Hi Fabrizio, can you post the service manual somewhere?
    Thanks.

  7. #7
    Nicholas Lindan's Avatar
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    You can't tell the value from the supplied picture. And gold doesn't always mean 5%.

    Some designs use resistors as very slo-blo fuses - never a good idea. But that does look like the case here - with the posts holding the resistor away from the board so that when it flames it doesn't set the board on fire. The resistor may unplug from the posts for easy change out.

    If the resistor was associated with motor current limiting then it may have blown if the motor stalled out or was run with a heavier than expected load from a gummed gearbox or some such.
    DARKROOM AUTOMATION
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  8. #8
    Steve Smith's Avatar
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    Does the unit still work properly despite the sparking resistor?

    The reason for asking is that judging from the close up picture, the resistor appears to be connected in series with the blue capacitor above it. If this is the case, it could be possible that the capacitor and resistor form a 'snubber network' which is connected across the motor connections.

    The unit will work fine without it as the purpose of a snubber network is to reduce electromagnetic interference from electrical contacts - in this case, the brushes and armature connections of the motor.

    If this is the case, the most common value for the resistor is 100 ohms (with a 0.1uF/100nF capacitor).


    Steve.

  9. #9
    Nicholas Lindan's Avatar
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    Looking at the video, Steve may be right -- it is a snubber across the motor. [When you said 'sparking' I thought it was in reference to the resistor being burned, not that it was actually sparking - they don't usually spark (or not for long)...] The snubber isn't there for EMI but to absorb the inductive kick when the motor reverses - well, there will be a burst of EMI from the relay contacts at reversal and it will help with brush noise but brush noise caps are usually right at the motor terminals. You can see the spark when the relay clicks and the motor 'whines in the other direction', though it only sparks on one of the two reversals. It could be the relay contacts are absorbing the spark in the other direction.

    The 100 ohm/.01 standard snubber is used for 110/220V AC circuits. It is my understanding the Jobo motors operate at 24V. The snubber resistor shouldn't have blown. OTOH, why a snubber should be up on spacers like that is a bit of a mystery. It is possible the capacitor shorted out, and that is what caused the resistor to burn/open. As it is a small cap the chances are the voltage rating is rather low. Try replacing the resistor with a 100 ohm 1/2W [a good a value as any?] and the cap with the same value but with a 200V or more voltage rating. The standard snubber capacitor is http://search.digikey.com/us/en/prod...756-ND/2687071 - but it is for 110/220 circuits.

    The busted snubber circuit won't be the reason the motor turns slowly, though. The resistor is open - if it were still good there would be no spark and in any case it takes no current from the motor.

    You should replace the snubber, though, or you will soon find yourself needing a new relay. The snubber keeps the relay contacts from pitting.
    DARKROOM AUTOMATION
    f-Stop Timers - Enlarging Meters
    http://www.darkroomautomation.com/da-main.htm

  10. #10
    Thiago Lara's Avatar
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    Wow! That's a wonderful feedback. Thank you all very much!

    Thanks for the info on the German guys, ath! I'll contact them soon. Right now I'm waiting a response from a US guy on the spare parts, lets see what's he gonna tell me first, since the shipping will be cheaper from US. Also, I already bought some itens from this guy that I'm waiting a response in the past, nice guy.

    Diapositivo, you're always saving me! Thank you very much. At this point any info will be worthwhile, since I'm already looking for alternatives for the board and the motor. I'll send you a PM.

    polyglot, I just googled (jobo motor hoffy site:apug.org) and found lots of information on this exactly same issue. Thank you very much for the reference, I wasn't found those threads on my earlier search. References to several repairs and modifications on a dead CPE-2.

    Hoffy's threads:

    http://www.apug.org/forums/forum43/9...-overhaul.html

    http://www.apug.org/forums/forum43/8...one-tried.html

    Other threads that may be useful here, still researching:

    http://www.apug.org/forums/forum43/8...pe2-dying.html

    http://www.apug.org/forums/forum43/8...processor.html

    I'll try call Hoffy and also Gregg Blank that ic-racer said here in this thread through PMs.

    Right now I think my best bet would be try to improvise some 24V input and try the motor alone to see what happens, right? Something like 3x 9v batteries (27V?) in series would do it? I also have a pair of 12V 5Ah batteries from a portable flash unit, if I wire them in series it would be 24V 5Ah, right? Can I test the motor with that? What do you think?

    About the controller board... I seeing that will be my real headache. Steve Smith and Nicholas Lindan, I think I'm failing in following you two here. Here's some more detailed pictures of the board:

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    Whats exactly the components you think I need to replace? Do you think I also need to replace the motor?

    Here's a video on the motor and it's noises, and some pictures so you can check if everything is wired the right way in the right places... the machine seem like was serviced before, some wear from instruments on the bolts, things like that... maybe its wrong connected somewhere, I don't know:



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    Thank you all very much for your inputs so far. Hoping to hear more!

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