Acquired a military multimeter AN-PSM-37,Intend to fix it

[daisizhou]

Want to know if any friends are still using this kind of multimeter?
Found that there are 5 legs of the op amp, I don’t know what model it is,Can anyone tell me the exact model number?
[ Specified attachment is not available ]

[xavier60]

The selectable voltage input  sensitivity including 10MΩ looks interesting. FET input stage maybe?

[daisizhou]

Yes, there is a 5-pin chip on the internal circuit board,Looks like an op amp
But did not write the model number
Below is the manual, hope you can help me 33A1-12-933-1_5029.pdf (2342.14 kB - downloaded 66 times.) 33K1-4-141-1_4468.pdf (747.27 kB - downloaded 85 times.)

[bob91343]

What is wrong with it?

[daisizhou]

Pointer does not turn,Estimated to be damaged

[xavier60]

Pointer does not turn,Estimated to be damaged

If  you have a working Digital Multimeter, you can do a resistance test on the meter movement's terminals.
I'm not certain what to expect at the moment but the pointer needle should also move.

[daisizhou]

Has anyone used this kind of meter?I hope friends who know or know can help me

[Stray Electron]

  The date of the contract for that meter appears to be 1974 but I've never heard of that company!  My guess is that they were a small shop that got part of a large contract to build meters (not a standard design either) along with many other small companies. I have a big "automotive electrical system" tester that falls into the same category. I've seen many "automotive electrical system" testers that were purchased under the exact same military classification as mine and meet the same requirements but they're all different and were built by at least 6 different companies. It's also quite likely that that company that built your meter only existed for as long as it took to build the meters to complete that one contract. FWIW the tester that I have was built in a town about 10 miles from where I live and I know many electronics types in the area and none of them have ever heard of the company!  However I got lucky in that even though my tester is about the same vintage as your meter, it had been completely overhauled in about 1982 and then placed in a sealed box that wasn't opened for about 30 years and it included two complete copies of the manuals for it.

[Stray Electron]

Pointer does not turn,Estimated to be damaged

If  you have a working Digital Multimeter, you can do a resistance test on the meter movement's terminals.
I'm not certain what to expect at the moment but the pointer needle should also move.

   That meter movement takes 50 microamps DC for Full Scale movement. It's marked on the scale.

[Stray Electron]

  Have you seen this?  http://www.nj7p.org/Manuals/PDFs/Military/TO%2033A1-12-933-11%201-May-87%20K4XL.pdf

   Look at the next to the last page.

[xavier60]

Has anyone used this kind of meter?I hope friends who know or know can help me

Can you post some internal photos?
Are the battery contacts intact?

[daisizhou]

Yes, I have checked this model.They look alike, and the internal circuits are basically the same
The only difference is the safety protection device

I am trying to disassemble it

[xavier60]

With no battery power, that multimeter will not even work on the voltage ranges.
More conventional analog multimeters need battery power only for the resistance ranges to work,

[Wallace Gasiewicz]

I have one of these meters and have repaired it. It is a good meter. Use it all the time. There is somewhat of a following of fans on some military equip post sites
It is more like a VTVM or modern digital meter in that it amplifies the input to achieve a high input impedance, so it loads down the circuit very little.
To check the mechanical D'Arsonval meter itself, just touch it with resistance probe of a multimeter.
There is a FET jnput and the op amp is pretty standard, as I recall.
This thing takes a LOT of batteries. I am attaching the Manual with some schematics.

Wally