Heathkit IM-25 Solid State VOM - Part 2: Battery Eliminator Hack & Final Reassembly

See below for a table of contents for this video.

Before watching this video, I recommend that you watch my Part 1 video about this Heathkit IM-25 solid state VOM.

In this video, which is part 2 of 2, I go into all details of the design, fabrication and testing of a battery eliminator created for this meter, essentially 'hacking' Heathkit's original design that required 18 (yes, 18) 'C' cells to form two battery packs (not counting the special 1.35V mercury cell used as a voltage reference), and I conclude with the final reassembly of the meter.

The IM-25 has special significance for me. It was the second Heathkit I ever built (as a teenager during a high school electronics class)....I had previously built a power supply, the Heathkit IP-27, and I have a similar YouTube video to this one for that power supply......BUT, the IM-25 meter was the first Heathkit that I never got to work at the time. Now, doing the restoration of the same model, acquired on eBay, I encountered what I think was the same issue I had back as a teenager, with the culprit being a few major errors in the manual's 'calibration' procedure. The difference between failure and success can be chalked up to knowing almost nothing of electronics as a teenager, contrasted to looking at it with the eyes of somebody who has done electronics design for 47 years, and and therefore able to figure out and correct the errors.

00:00 Battery eliminator hack
28:55 Fabricating the custom PCB for the battery eliminator
1:06:47 Final re-assembly of the restored meter
1:09:20 Beauty shot

[stephenstoner]

Hi, I found your you tube site by acident and also have a IM25 meter that i would like to restore. I am very intrested in building a battery eliminator but wondered of you havew avalable a circut board layout (or a board avalble for purchase?), parts listing and so forth avalable. certainily appreciate all your eforts and high quality video presentation. Steve Stoner

[johnaltamura]

Our family just drove by Gurnee on the way back to Wisconsin. Always remember you talking about it on one of your train videos. Thanks for the great content!

[marka]

Wondering if you could have tacked the primary wiring for your battery eliminator board to the primary of the main transformer instead of the board traces. Nice meter. I like that it has the .15 volt range. Nice restoration and explanation of the cicuit.