Heathkit

IM-18 VTVM Restoration

 

Initial condition of the IM-18 VTVM as received from the seller. Note how the cabinet paint is peeling off and the cabinet is put on upside down!! The ID label was put on  between the handle and the top of the cabinet. When I powered up the IM-18 I noticed the transformer got warm which should never happen. There was an obvious short somewhere, possibly in the wiring or on the PC board. The original or a previous owner scratched their social security number on the to rear of the cabinet. The short was found in the power indicator lamp socket. Replace the socket, problem solved. The other problem was the PC board was cracked resulting in numerous broken foil runs. I fixed the broken foil runs with jumper wires and gled the breaks in the board.

The other problem was the original builder or a previous owner connected the AC HOT to the PC board’s “LINE” connection and the AC NEUTRAL to the Function switch rear wafer terminal 2. I used the Function switch rear wafer terminal 2 for the AC voltage source to perform the AC CAL adjustment. Applying AC HOT to the “LINE” connection, the AC voltage would drop across the power transformer primary winding resulting in zero AC volts at the Function switch rear wafer terminal 2. This prevented the AC CAL adjustment from being done. I swapped the AC HOT and AC NEUTRAL power cord wires so AC HOT was on the Function switch rear wafer terminal 2 and the AC NEUTRAL  was on the PC board LINE connection. It’s best to switch AC HOT like the manual says then to switch AC NEUTRAL. After making the swap, I was able to perform the AC CAL adjustment so the meter display 118VAC (my normal AC wall outlet voltage) without any problems.

 

As the IM-18 looked when received from eBay seller

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Rebuilt IM-18