Restoring a pair of 1968 Heathkit IM-18 VTVM’s

Thorough repair of two

Heathkit

IM-18 VTVM’s

 

Repair update 02/10/2018

Initial condition of both IM-18’s as received from the seller

Both IM-18’s have the same flaky cabinet paint problem. One IM-18 meter cover was cracked and a previous owner tried to fix it by gluing, didn’t do a good job. The other IM-18 meter was stuck, damaged beyond repair. The stuck meter was swapped out with a spare I had. The replaced meter works 99%, had a slight issue with accuracy so a second spare meter was found on eBay and is schedule to arrive on Monday 12 Feb 2018. The second IM-18’s handle was broken.


Complete restoration of two IM-18 VTVMs


 

 

 

The replacement meter arrived today. I swapped out the meters and now the second IM-18 works as it should, no taping the meter so the meter rises to the proper point on the scale. The 200ua meter’s internal resistance is approximately 908 ohms. Not all meters will have the exact same internal resistance. Using Ohms law the voltage across the meter terminals at FS (Full Scale) is approximately 181.6MVDC (0.0002 x 908 = 0.1816VDC),