Mcintosh Volume control acting erratic

Have you tried unplugging the unit and resetting the pre-amp? Since it has a micro-processor in the volume control,it may have had some brain flatulence and just needs a re-bbot. If that doesn't do it call Chuck Hinton at Mcintosh if anything they will fix it under warranty.
I have had many Mcintosh pre-amps and have bfound the re-boot to fix any quirks. When it didn't Chuck helped me out.
Good people, great equipment.

My MX 132 will sometimes need to be re-booted, which means turning off the main switch and leaving it off for a few minutes. No big deal

It could be a static discharge when you touch the unit. That is what happened to mine. Simply turn it off and unplug for a few minutes and you should be good to go like Theo says.

I have had a similar problem for some time to the point where the only way to change volume is via the remote. I spoke to the folks at Mcintosh who told me if the reset doesn't solve the problem, it will need to be sent for service. I would be less bothered by this if the remote weren't so cluttered. Anybody know of a quality programmable remote-somthing like Simaudio's-to provide very basic functions. Volume control is all I need

Depending on how many compnents you want to program into a remote I have the marantz RC1400 and love it. I had the RC2000mkII and that was good but not enough memory. But I run my whole system 9 componnents with this little remote and a couple of macros. I like the ability to punch through other component functions to each component screen.

As an Authorized McIntosh repair center, we have had more than 2 Optical Encoders fail (one in an MX-132 and another in a C2200 I seem to recall) and they reflect your exact symptoms when failing. Take her in for service and McIntosh will take care of you.

My problems is not only does it get stuck, but it changes on it's own. I have a computer modem within 3 feet and am wondering if that could cause it.

I don't think the modem is the culprit here. Mcintech has the best advice.

I serviced the encoder on my C46 tonight. It's a serviceable part, the top slides off exposing a small board. On mine, I noticed a few suspect joints, I addressed with my station and needle tip. I cleaned the sensors, 2 pairs which read the wheel from both sides with alcohol. I also was able to wipe off the wheel itself with a Q-tip and IPA. Reassembled, it's 95% I'd say. Unsure if it was the suspect joints or the alcohol, but thankful it was such a quick, easy fix I was able to do myself within a half hour. Behavior I was experiencing was not skipping on its own, but unresponsive to manual turns, leading the user to turn quickly or very slowly to gain desired movement.