Sunday, May 18, 2014

Chroma Polaris Membrane Repair

While repairing a Chroma Polaris, I was forced to disconnect the ribbon connectors (technically FFC connectors) that connect the membrane to the panel PCB's. To my horror, even though I was being painstakingly gentle and slow, one of them tore, almost immediately, as soon as I tried to move it

Additionally,  the other 3 connectors -which didn't break as the first one did- still became cracked and intermittent when they were unbent from the position they had been resting in for 35 years.

In all cases, the cables broke where they had been bent... fairly close to the socket.

To repair the situation, I was able to cut the damaged portion off with scissors, and then grind away the insulating material (from the black side, not the silver side) with a wire brush attached to a dremel.

This may seem barbaric, but it actually worked flawlessly. ( I practice on the discarded portion of the ribbon cable first). You just need to buff it just enough so that you are able to ring through the traces on the ribon cable with your multimeter. If you buff it too much, you will grind through the conductive material, and render it useless. So you have to buff, and test, buff and test, until it rings through. It is naturally a good idea to practice first on the discarded portion of the ribbon cable.

On 3 of the connectors, I didn't have to shorten the cables too much, and they still stretched to their sockets

. On the 4th, I had to install a few wires and actually move the socket closer to the cable.

Either way, the repair has seemed to be permanent and hopefully the membrane will last another 30 years, especially if it is undisturbed. An additional step may be to recoat the exposed conductive part with conductive epoxy or paint; however it did not seem required in this situation.

One additional note: these flat ribbon cables are actually called FFC's, flat flexible cables. They are not called ribbon cables at all. Ribbon cables, technically, are made up of many insulated wires attached to each other. If these break, it is much easier to repair them. I am going to put up another post discussing FFC cables.

I also recapped the power supply and replaced a few faders.


No comments:

Post a Comment