Analog Meter Repair - Fix or Fail? Heathkit IM-5218

Removal and cleaning of a sticking analog meter from Heathkit VTVM model IM-5218. Note: This VTVM has been converted to solid state and no longer used tubes.
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[@killercloud7019]

John some info I found while googling the IM-18 The IM-18 VTVM was one of my favorite tools. It was one of those basic designs that couldn't be improved upon. The circuitry was essentially the same since it was introduced (under a different model number) back in the '50s. The circuitry hadn't changed in the late '70s when it was later given a new paint job and the model number changed (Marketing moves in mysterious ways). Anyway, it was a rugged tool. In the '70s, Heath came up with an upgrade (the IMA-18-1) that replaced the two vacuum tubes with solid-state equivalents so that it would be ready the instant you turned it on. I did a lot of warranty service on the modified units as they tended to blow up when brought near the high-voltage circuits in color TVs. I think most customers who bought the mod went back to the vacuum tubes. Needle pegs on DC or AC on first turn-on: Suspect a leaky DC-cal or AC-cal potentiometer. ww_heco.home.mindspring.com/heco_fix.html From: Heathkit Troubleshooting tips

[@TinkerJohn_W5CYF]

Thanks for taking time to leave the detailed comment and suggestion. That's good info. ~John

[@zarchy55]

I had the same VTVM years ago. I also performed the same solid state conversion. The modules were available from Heathkit, if I remember correctly.

[@TinkerJohn_W5CYF]

Thanks for watching and providing the info on the solid state conversion kit. ~John

[@zarchy55]

I don’t remember if the two solid state modules were physically interchangeable, but check to see that they are plugged in to the right tube sockets, contacts are clean, etc.

[@jamescoffey5225]

The two solid state modules are not interchangeable! I have the old Heathkit VTVM (non functional unfortunately and I don't know why) with the solid state modules installed. The instructions for installing them also required some minor circuit modifications (removing a couple of components--not difficult). John, if you want the modification instructions and the changes to the schematic, please contact me and I will email them to you. I think I still have them. 73 de Jim, AE5ZX

[@jameslester3861]

I built one of those in vo-tech school in 1979 and still have it. I don’t like the design of the probe on it but it’s a nice meter.

[@TinkerJohn_W5CYF]

James, thanks for following along. Those were some nice meters. ~John

[@skycarl]

I'm partial to Heathkits as well John. I have a V-7a VTVM.

[@TinkerJohn_W5CYF]

Carl, always good to hear from you. I"m really enjoying your AM radio and amp series videos. Good stuff! ~John

[@warplanner8852]

John, if the two modules merely plug into the sockets and that's the extent of the mod, you can remove them and replace them with a 12AU7 and 6AL5 and restore the meter to original condition. Those tubes are available on eBay. Bill, k6whp

[@TinkerJohn_W5CYF]

Bill, thanks for that info. I was wondering if that was the case. I don't have any info on the solid state mod so this is very helpful. I"ll be on the lookout for some tubes. ~John

[@jamescoffey5225]

See my comments below "somewhere." You just can't remove the solid state units and replace them with original 12AU7 and 6AL5. Circuit modifications were required as part of the installation procedure for the solid state units that replaced the VTs. 73 de Jim, AE5ZX

[@zarchy55]

Yes, the mod consisted of simply replacing the tubes with the plug in modules. That’s the way I remember it., anyway. You might be able to pick up a 12AU7 tube at Guitar Center. I believe the 6AL5 tube is only used for the AC function. You should probably concentrate on getting the DC mode to work first before spending a lot of money on parts.

[@jamescoffey5225]

I just checked my old (nonfunctional) Heathkit VTVM (w/ SS mods). My model is the (older) IM-18, not the IM-5218. Looking at my old schematic, I had to change out a resistor in the circuit and replace it with another one of a different value as part of the solid state modification to the VTVM. I did this "decades ago" so I don't recall much else about it. The problem with my VTVM is not with the meter, however.

[@happymark1805]

you found a lot of gunk, well one of the previous owners was probably a smoker, so that means everything is covered with that gunk, first begin with cleaning all the contacts of the switches and potentiometrs and then see what happens, after that, well you have the manual.

[@TinkerJohn_W5CYF]

Thanks for the good suggestion. I am cleaning up all pots and switches. I'll see where that take me. I really don't "need" this thing, but mostly after the fun in getting it going. ~John

[@williamthrasher8540]

you may have some bad capacitors. Leaky caps maybe allowing to much voltage across the meter terminals.

[@TinkerJohn_W5CYF]

William, I think you're on the right track. I've put the meter on the back burner for a few weeks and will look at caps when I get a chance. ~John

[@eldonwilson8495]

John If you want a working vacuum unit, I have a HeathKit IM15 that works. Dont use is any more. Want it?

[@TinkerJohn_W5CYF]

Eldon, Thanks for the offer. If you are not using the VTOM, I'd like to work out a deal with you. Contact me via PM and we can go from there. All the best. ~John

[@inerlogic]

I have an IM-18 (with tubes) the ohms function works, but i get nothing on the AC/DC ranges. I've replaced the two non-ceramic caps. If anyone has suggestions as to what to check, i'm looking for suggestions :)