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 Post subject: Heathkit IM-103
PostPosted: Nov Sun 17, 2019 2:55 am 

Joined: Dec Wed 24, 2014 7:34 pm
Posts: 2090
Location: Weimar, Texas
I picked up a "very nice" IM-103 on eBay a few weeks ago. Here's the ad on eBay:

This is a very nice Heathkit IM-103 line voltage monitor. <--- Define nice

The paint is factory original. <--- True

It has been recently calibrated. <---- Ummm does calibration involve smoke and flames? :lol:

The original manual is included. <--- indeed and it came in handy

This is what I received (note the zener diode replacement stack and other questionable wiring)-


This is what I turned it into. It calibrates fine after replacing... everything but the meter.


I have three of these now. I think I may have a Heathkit problem... I don't leave them plugged in because they get a little warm but when the ham rigs are fired up or I'm working on the bench I plug them in. I upsized the voltage or wattage ratings when I restored them. All three were smoke calibrated :shock: :D prior to purchase. For some reason the seller always claims they are in perfect working order :D They are now :) I always just strip the board, switch, pots, and meter out oif the case and wash the smoke out as best as I can. The board gets stripped of components and desoldered.

There's a 16.1V zener in the circuit. A 16v 1/2W zener works fine. I didn't take a photo of the face and sides but it really is clean.

It's hard to solve an equation if every term is an unknown.



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