Old heidenhain scale ratio problem - Page 2
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  1. #21
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    Yes, it's consistent throughout the travel...and it is exactly 25%....give or take ancient Bridgeport tolerances! I've got access to a handheld vacuum desolderer, but I've got the weekend to mull over if I can be bothered��

    Wish it'd just been the switch��

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    Quote Originally Posted by darkhorse0 View Post
    Yes, it's consistent throughout the travel...and it is exactly 25%....give or take ancient Bridgeport tolerances! I've got access to a handheld vacuum desolderer, but I've got the weekend to mull over if I can be bothered��

    Wish it'd just been the switch��
    Boffins? Is it works correctly in imperial, which chip is likely to do that 1/25.4 thing.

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    Quote Originally Posted by darkhorse0 View Post
    Another thought....the electronic side of things is above my pay grade, but I can solder. Most of the chips seem to be available at negligible cost, is it worth just swapping them all out? Are any of these more likely to be the culprit than any others?
    M9102 I assume some kind of buffer
    LM339 Quad comparator
    HEF4081BP Quad 2-input AND-gate
    HEF4013BP Dual D-type flip-flop
    HEF40174BP Hex D-type flip-flop
    SCL4070BC ???
    HEF4027BP Dual J-K flip-flop
    HEF4011BP Quad 2-input NAND gate
    SCM10007P ???
    HEF4001BP Quad 2-input NOR gate
    HEF4516BP Binary up/down counter
    SCM1010BP ???

    Thanks in advance..

    SCL4070BC Quad Exclusive-OR Gate

    Do the SCM10007P and SCM1010BP have more than 16 pins?

    Post a pic of each will help.

    Bill

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    I am following this thread with interest; I am also trying to repair a fault in a 731B unit. (One channel will only count up, no matter which direction the encoder moves.)

    A bit more info in reply to an earlier comment; the boards appear to be triple layer, so a bit more complex, but still possible to follow without too much effort.

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    If you are re-chipping it, might pay to get some sockets in there, makes things way easier going forwards. Chips are cheap, you can also get logic chip testers pretty cheap too, on socketed boards a quick removal drop in and press of the test button can find the failed ones in minutes.

    Other favourite trick of mine is inspecting the power supply on older digital electronics like this. Hell maybe even just replace the smoothing capacitors on it, also check it for correct voltage too. Some times borderline voltage + a bit of electrical noise can play hell on digital electronics of that period!

  7. #26
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    It looks like the OP may have given up on this old thread.

    Anyway, this is a digital system. So any power supply or capacitor issues would probably lead to either complete failure or somewhat consistent problems in both English and metric measurements on both scales, not just a metric problem on one scale. Noise on the power supply would probably produce random results on all scales.

    It is most likely not a 25.4 thing because his factor is 80% (0.800X or 1.25X if you invert it) and he says it is as exact as he can measure.

    It is not likely a wiring problem as the wiring will be the same for both English and metric.

    As for an individual chip, that is a bit more complicated. It could be, but with many years of experience in troubleshooting digital electronics, I would highly doubt it. More likely a broken trace or bad solder connection on the board.

    As I said early in the thread, it is MOST likely some kind of calibration constant that is held in a memory or that is switched with some kind of switch or jumper. Or that is actually entered into a memory by some combination of button presses. The scales will have a basic count that is finer, probably much finer, than the resolution of the scales. Something like 10 or more counts for each 0.001" increment or hundreds of counts per mm. This is divided down by the electronics and the correct factor must be used for each mode.

    If he is still trying to repair this unit, the best way may be to find a copy of the original instructions and read them.

    Another approach may be to take some GOOD, CLEAR, CLOSE-UP photos or the boards (both sides) and any other controls and post them here so I/we can see them. With 45 plus years of experience, I can't remember everything, but a photo can quickly bring back some of those long buried memories.

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    I have some questions about a problem with the same 731 Heidenhain DRO controller. I have posted a question in the Bridgeport forum, but the only reply I got was to direct me to this thread. I don't want to hijack the thread, but I am happy to post pictures of the boards which may help both me and the OP.

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    Here are some pictures of the DRO boards. Please ask if any of the IC numbers are unclear.heidenhain_731_display_rear.jpgheidenhain_731_display_front.jpgheidenhain_731_input_rear.jpgheidenhain_731_input_front.jpg

    The problem I am having is that one channel will only count up, no matter which direction the encoder moves. I have swapped the encoder and the problem stays with the channel.

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    RE: the original poster's question. Those two boards appear to each have three devices, vertically (in the photos) across the middle of the boards. I can not make out what they are. Are those DIP switches or jumpers? That could be where the scale factors are entered.

    RE: count up but not down. That would be a more difficult problem. It could be a bad chip. Or just a broken wire. Have you carefully checked the connections. And just what do you mean by "not down"? Does it just stop counting when you reverse direction or does it continue to count up?

    A schematic would really help for that. Anybody know if one is available?

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    The blocks in the middle of the boards are pin connectors to link the 2 boards.

    re count up not down; the numbers will go up if you move the encoder in one direction, and continue to go up if you move it in the other direction.

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    Sounds like there is a direction signal that is not changing.

    What do you have for troubleshooting equipment? Scope? Digital probe? Multimeter?



    Quote Originally Posted by NickA View Post
    The blocks in the middle of the boards are pin connectors to link the 2 boards.

    re count up not down; the numbers will go up if you move the encoder in one direction, and continue to go up if you move it in the other direction.

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    I've got a scope and a multimeter. I may be able to uncover a logic probe hidden somewhere. I am pretty unskilled with the scope, so any pointers would be much appreciated.

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    I have managed to track down the circuit diagrams for the VRZ 731B DRO, If I post them here, is there someone who could help me interpret them as to where the signal to change from up to down (or vice versa) is getting lost?

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    Quote Originally Posted by NickA View Post
    I have managed to track down the circuit diagrams for the VRZ 731B DRO, If I post them here, is there someone who could help me interpret them as to where the signal to change from up to down (or vice versa) is getting lost?
    Hi Nick,
    Im having 731b trouble, x wont count up or down. can you send me your circuit diagrams please?

  16. #35
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    i wonder if op has found a solution.

    (one of my axis reads 75%. i got used to it after a while.)

  17. #36
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    i finally solved my 731b x axis counting problem and it only cost me €1! i added a thread here for anyone interested
    Old heidenhain 731b fault repaired without diagram


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