Help troubleshooting an old Audiocom intercom

[cmoore]

I'm trying to resurrect an old (late 80s) Audiocom IC-2MAX master station. It seems to be basically functional, but I've got one problem - every time I throw a switch, for example, to turn on the mic, there's a loud pop in the headset. Same thing when I switch one of the two channels on or off.

I am using a cheap Califone headset that I hooked up to an XLR connector.

Could it be an issue with the cheap headset? Or dirty switches in the station? If anyone has any ideas I'd be grateful.

Also, while I'm at it, I picked up a Telex IC-4M too. It needs a little more work than the IC-2MAX. If anyone knows where I could find schematics that would be great too.

Thanks.

 

[FMEng]

It could be a dirty switch, but I would place my bet on one or more bad capacitors. A very common failure in all old electronics is the electrolytic capacitors drying out from warmth. If you are handy with a soldering iron, the easiest thing to do is replace all of the electrolytics. Won't cost more than a few dollars.

 

[cmoore]

It could be a dirty switch, but I would place my bet on one or more bad capacitors. A very common failure in all old electronics is the electrolytic capacitors drying out from warmth. If you are handy with a soldering iron, the easiest thing to do is replace all of the electrolytics. Won't cost more than a few dollars.

Excellent point, thanks! I did find a schematic for a IC-3M. I'm guessing the basic circuitry should be similar, so I should be able to start with the more likely caps.

I did notice that, after hooking it up to the IC-4M, switching the mic on and off on the IC-2MAX also causes the loud pop on the headset on the IC-4M. That tells me that the spike is actually making it onto the channel itself, it's not local to the one unit. Next step will be to track down how that switch interacts with the channel.