Need new potentiometers for IBM 5155

[dhau]

When I adjust contrast and brightness, CRT image jumps erratically. Is it possible to replace potentiometers with new exact equivalents?

If that is not possible, can I somehow refurbish old ones?

 

[Chuck(G)]

You can find replacements, but the easiest way to handle this is to simply clean them. Near where the terminals on the controls are should be a small gap in the case--squirt some contract cleaner in that gap and rotate the control. Usually, this will take care of things.

 

[maxtherabbit]

I like deoxit for this

 

[Hugo Holden]

The gap that Chuck talked about, where you can squirt in the cleaner, and sometimes other gaps where the cover does not completely seal the control, is the gap that let dust and vapors and fumes into the control, sometimes cigarette smoke etc. This tends to insulate the control wiper from the carbon track and make for intermittent connections. I generally will clean the control first with contact cleaner (such as CRC's CO contact cleaner) rotating the control back and forth over its full range. After the cleaner dries though, the friction can increase so I spray in some Inox mx-3, which provides long lasting protective lubrication (it is better than any other product for potentiometers, switch contacts, IC sockets etc). Although there are "cleaner-lubricant" products, none are as good as separate clean and lubrication with mx-3.

Very long lasting controls are normally completely sealed units.

 

[Chuck(G)]

Sometimes the things just wear out. Not long ago, I replaced the throttle position sensor (basically a sealed pot) on my truck. This was the second time I did the replacement in 29 years. Wacky Ford engineers put it on the bottom of the throttle body, so you have to disassemble the thing to get to it. (5.0L V8). Have a replacement gasket handy.

 

[Hugo Holden]

Sometimes the things just wear out. Not long ago, I replaced the throttle position sensor (basically a sealed pot) on my truck. This was the second time I did the replacement in 29 years. Wacky Ford engineers put it on the bottom of the throttle body, so you have to disassemble the thing to get to it. (5.0L V8). Have a replacement gasket handy.

Yes, sometimes the track can wear its way right through the carbon coating. If this has happened the resistance across the potentiometer end terminals will increase a little.

But often, there is a fix, if you bend the wiper arm so that the small projection from it, which wipes across the carbon track, is on a different radius of curvature, then the potentiometer's function returns to normal..or is "repaired". These are the things you come to learn when you are stuck in a garden shed, with no replacement parts, in Timbuktu.

 

[Chuck(G)]

I will confess to making a midnight repair on a bad pot by using a soft "lead" pencil to fill in a gap in the track.

Good luck on getting into one of these:

 

[Hugo Holden]

I will confess to making a midnight repair on a bad pot by using a soft "lead" pencil to fill in a gap in the track.

Good luck on getting into one of these:

I had heard of that idea to use a pencil on the worn tracks, but I have never tried that one myself.