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208Re: Electronics on KH970 CB1

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  • Steve Conklin
    Apr 16, 2012
      Cobi (and list),

      Sorry to take so long to respond -

      First my disclaimers - I know nothing about the KH970, but am basing
      this upon what I know about the KH930 and technology of that era.

      If the following is difficult to follow, please email me directly, and
      I'd be happy to discuss this with you on the phone.

      The short version is that your machine might be repairable in the
      hands of someone with some electronics knowledge. These machines are
      so hard to ship without damage, or I'd offer to look at it for you.
      Where are you located? (no need to be too specific) Maybe we can find
      someone near you with the right skills to help you.

      The electronics on those those machines are built using a low level of
      integration and generic through-hole parts. In basic terms, this

      0. They are often repairable
      1. There are a lot of parts on the board
      2. The parts are generally common devices and still available, with
      some exceptions
      3. It's not uncommon to have failures which result in loss of one area
      of functionality (floppy disk connection, for example)
      4. In the CMOS chips used in that era, common failures include damage
      due to static electricity, which commonly happens on chips connected
      to external connectors like the floppy connector.
      5. With some time and electronics knowledge, it's often possible to
      find and fix these problems.

      Since the machine knits using internal patterns, we know that the
      internal microprocessor and the control electronics work. This is
      good, because it means that most of the parts which are likely to be
      "impossible to replace" are working.

      I think it's probable that your machine has a failure in the chip(s)
      which connect to the floppy drive connector. For someone with skill in
      electronics, it might be possible to diagnose and repair this. If it
      were me and it were my machine, I'd open the machine and try it, but -
      it's not my machine, and I'm pretty experienced and comfortable with
      these things.

      As I recall from the KH-930, the chip connected to the floppy drive
      was a simple 4xxx series CMOS logic part, a hex inverter or quad NAND
      or something like that. These are very easy to get.

      If it were my machine, here are the steps I'd take:

      1. Take anti-static procedures - work on a conductive mat or even a
      piece of anti-static packing foam. Wear a grounding bracelet connected
      to the mat, and connect the knitting machine frame to the mat.

      2. Remove the cover and examine the board with the floppy connector.
      Figure out which chip the traces from the connector connect to, and
      sketch out the pinout of that connector and label everything.

      3. (If possible) Connect the floppy drive and power up the machine and
      the drive. Using an oscilloscope, check the signals at the inputs and
      outputs of the logic gates on that chip, and try to verify that one of
      them is not working as it should. Try to observe it when attempting to
      save a pattern, etc. Continue diagnosis, hopefully until a bad part is

      4. Order a replacement part. If the original part is a 4000 series
      CMOS part, it will have a number like CD4009 or CD4012. If the
      original part has no suffix or an 'A' suffix, then death due to static
      electricity was almost certainly the problem - the original A series
      parts were very susceptible. You will replace it with a B series part,
      as that's all that's available now - it will work fine.

      5. Note the orientation of the old part. One end will have a notch, or
      perhaps a molded dot on the corner. If the PC board isn't marked, you
      can make a mark with a marker near that end. Be sure to put the new
      part in the same way.

      Carefully remove the bad part and replace it. If you don't have
      desoldering equipment, then with through-hole Dual-Inline packages
      (which this probably uses) the best way to do this without risk to the
      board is to clip each lead close to the chip using a small pair of
      flush cutters, and remove the chip body. Then using hemostats heat and
      remove each pin. Now remove the excess solder from each hole. This is
      really the step which is most likely to cause damage to the board,
      which may be hard to repair. There are several ways to do this and
      it's a topic unto itself, so here's a web page which does a good job
      of discussing it: http://www.aaroncake.net/electronics/desolder.htm

      6. Install the new part and solder it in place.

      7. Test the knitting machine, and put it back together. If it doesn't
      work, keep troubleshooting.

      This sounds daunting, but it shouldn't be more than a few hours work,
      even at a relaxed pace (not counting ordering the part). The
      electronics in these machines is actually more repairable than a lot
      of recent electronics, but it takes some time.

      I hope this is helpful,

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