Rebuilding ARP PPCs

Using FSRs (force sensing resistors) to repair PPC "proportional pitch control" pads for an ARP Odyssey Mark III

Because I am now one of those people who thinks they are very busy, I am just going to share a “quick tip” today.

In one of several Odysseys that we rebuilt recently, the “Proportional Pitch Control” pads (otherwise known as PPC, those three spongy white pads that Mark III Odysseys have) were so bad that no amount of cleaning could revive them. I finally was forced to look for another solution, and tried using some FSRs (force sensing resistors) and the results were great.

I was prepared to have to adjust some values of the mixing resistors following the FSRs but the ones already there were just fine. The FSRs I used are Interlink FSR-02 which I got from Digikey.

After cutting off the elements of the original PPC “sensor”, which appear to be just parts from inside a regular ARP slider, I glued the FSRs onto the original PPC PCB with a very thin layer of CA glue (super glue) applied with a Q tip, folded the “tails” around to the back and soldered a very thin (26awg) between each tail and the solder pads on the PCB.

If you’re doing this, the biggest challenge is how quickly the plastic that the FSR is made of can melt. With my soldering iron on 725, I basically melted the end off of the first one I tried to solder to almost instantaneously. Set your iron temp a bit lower and work very quickly and you should be fine.

One thought on “Rebuilding ARP PPCs”

  1. ugh.
    you just induced a nightmare ;0)
    one of the 3d printing systems we sell, and that i have to service, uses one of these for its calibration routine and to sense the nozzle has reached its limit on the z axis [rather than a simple endstop switch like it uses on its other axes].
    the fright comes from the fact that it’s about 5mm across – the pressure area is about 3mm – and it has to have it’s 2 tiny leads tinned JUST right to fit into tiny little push in sockets, and the folded over and stuck to a metal frame after removing a thin membrane that covers the self adhesive spot on back.
    if you touch the adhesive once it no longer sticks. at all.
    if you fold it too much or more than once the leads break off.
    if you put too much solder on when you tin it it won’t fit.
    too little and it does not stay in place.
    then it gets a plate put over it with a seriously sensitive hex key adjustment to set the starting pressure.
    too much pressure and you’ve killed it and have to start over again.
    and re-assembling the module it goes in requires 4 hands but barely has room for 2.
    and you have to re-assemble the printer to set the pressure and find out if it’s working – no way to test it prior to assembly.
    my boss was wondering why it took me 3 days to fix one of these the first time.
    then i showed him the badly translated from polish instructions and what the parts looked like and what was required.
    i really hate working on these machines.
    the company refers to it as the tensometer.
    that’s not the word i choose to use.

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