07-12-2014, 11:16 PM
Hi everyone hope this is the right place for this.
I was hoping someone could help me troubleshoot my Heathkit Im-28 VTVM. When I put the dial to DC+ the meter moves all the way over to the right then after a few seconds it goes back to the left which from what I understand is normal in either DC+ or DC- positions. Now, when it moves back to the left My zero adjust doesn't do anything, it wont move the meter at all. If I move the selector to DC- the meter then stays to the right and doesn't move back to the left. The troubleshooting page suggests to check capacitor c6 and resistors R35, 37 and 38 but they are good. I even changed C6 to 22uf 450v to be sure it was good. I did notice that with the variac set to 110volts coming in I have 123 volts ac coming out of the transformer and across c6, and if you measure DC at the + side of c6 I get 108 volts instead of 50 to 70 volts and on the - lead I get 42 volts which should be 60 to 85 volts. I have attached the schematic, I am hoping someone has an idea of what might be going on here. Thanks anyone for any time on this matter, I don't really want to buy another vtvm so I am hoping I can find the problem here. Warren
[Image: http://i1348.photobucket.com/albums/p721...84cbb8.jpg]
I was hoping someone could help me troubleshoot my Heathkit Im-28 VTVM. When I put the dial to DC+ the meter moves all the way over to the right then after a few seconds it goes back to the left which from what I understand is normal in either DC+ or DC- positions. Now, when it moves back to the left My zero adjust doesn't do anything, it wont move the meter at all. If I move the selector to DC- the meter then stays to the right and doesn't move back to the left. The troubleshooting page suggests to check capacitor c6 and resistors R35, 37 and 38 but they are good. I even changed C6 to 22uf 450v to be sure it was good. I did notice that with the variac set to 110volts coming in I have 123 volts ac coming out of the transformer and across c6, and if you measure DC at the + side of c6 I get 108 volts instead of 50 to 70 volts and on the - lead I get 42 volts which should be 60 to 85 volts. I have attached the schematic, I am hoping someone has an idea of what might be going on here. Thanks anyone for any time on this matter, I don't really want to buy another vtvm so I am hoping I can find the problem here. Warren
[Image: http://i1348.photobucket.com/albums/p721...84cbb8.jpg]
