Heathkit IM-103 Line Voltage Monitor - The Good, The Bad & The Ugly

If you have or are acquiring a used IM-103, here's the right way to restore it for proper use, as well as some examples of, let's say, poorly built ones.
I've had mine, now updated with modern parts, running for 52 years...

[@jadney]

I found mine about 20 years ago. Like all the others, it had burned up inside and was no longer working, but the meter movement was still fine. I'm amazed that this design ever made it out of Benton Harbor. I redesigned the circuit, changing resistor values so that it would work the same, but not overheat anything while not requiring anything above 2 W. Sorry, I don't recall the new values. It's been working fine ever since then. Someone on ebay is selling Heath upgrade packages to fix these. I've always wondered whether these just maintain the old design with higher wattage resistors or a more thoughtful approach that dissipates less power.

[@dtss_smudge]

@jadney : You're referring to the d8apro.com IM-103 rebuild kit. I looked into it, and it's not a bad kit but does not replace every component, just most of them. Also, as I show, all parts are available on DigiKey for ~

[@tomschmidt381]

Interesting, I have one I built in the 1970s, forget exactly when. I repackaged mine with a 5A AC meter a variac and isolation transformer. Now that you mentioned resistor overheating it I'll have to check mine. Have not looked inside in years.

[@Micotech1]

Yep, they blow, I've restored mine as well and improved it too, the electrolytic was temperature-sensitive and drifted in time, it was the first component to change, resistors change value as well here.

[@mikescott58]

Great video. I built many Heathkits back in the day. I still have my IM-103 and it still works. I think I built it back in '74 or '75. I will definitely replace the 50-year-old electrolytic and I like the idea of a grounded line cord. BTW, how did you strain-relief it? 3 wire cords are thicker. Did you drill the entry hole for a larger Heyco? I'll also replace the 2W carbon resistors with 5W wirewound, though neither looked like they suffered heat damage. Also, mine included the fuse.

[@dtss_smudge]

@mikescott58 You perceptively noted that I kinda did not show the line cord entry. The proper way to deal with a new flat line cord would be to taper-drill out a larger hole for a proper "sqeeze"-type (Heyco?) line cord strain relief, as I did for my signal tracer video. For now I did not want to modify the case, so I used a couple of zip ties on either side and a bit of silicone. Were I to sell one, I'd go back and do the right thing. Thanks for commenting!