Acquired a military multimeter AN-PSM-37,Intend to fix it - Page 1
Forum section: electronics / repair

author: daisizhou
author_rank: Super Contributor
timestamp: February 27, 2021, 03:48:21 am
content: 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 ]

author: xavier60
author_rank: Super Contributor
timestamp: February 27, 2021, 04:47:21 am
content: The selectable voltage input sensitivity including 10MΩ looks interesting. FET input stage maybe?

author: daisizhou
author_rank: Super Contributor
timestamp: February 27, 2021, 04:56:06 am
content: Yes, there is a 5-pin chip on the internal circuit board,Looks like an op ampBut did not write the model numberBelow is the manual, hope you can help me33A1-12-933-1_5029.pdf(2342.14 kB - downloaded 86 times.)33K1-4-141-1_4468.pdf(747.27 kB - downloaded 102 times.)

author: bob91343
author_rank: Super Contributor
timestamp: February 27, 2021, 06:24:25 am
content: What is wrong with it?

author: daisizhou
author_rank: Super Contributor
timestamp: February 27, 2021, 08:16:35 am
content: Pointer does not turn,Estimated to be damaged

author: xavier60
author_rank: Super Contributor
timestamp: February 27, 2021, 10:59:51 am
content: Quote from: daisizhou on February 27, 2021, 08:16:35 amIf 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.

author: daisizhou
author_rank: Super Contributor
timestamp: February 28, 2021, 04:51:57 am
content: Has anyone used this kind of meter?I hope friends who know or know can help me

author: Stray Electron
author_rank: Super Contributor
timestamp: February 28, 2021, 05:22:31 am
content: 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 gotpartof a large contract to build meters (not a standard design either) along with many other small companies. I have abig"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 knowmanyelectronics types in the area andnoneof 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.

author: Stray Electron
author_rank: Super Contributor
timestamp: February 28, 2021, 05:24:48 am
content: Quote from: xavier60 on February 27, 2021, 10:59:51 amThat meter movement takes 50 microamps DC for Full Scale movement. It's marked on the scale.

author: Stray Electron
author_rank: Super Contributor
timestamp: February 28, 2021, 05:28:50 am
content: Have you seen this?http://www.nj7p.org/Manuals/PDFs/Military/TO%2033A1-12-933-11%201-May-87%20K4XL.pdfLook at the next to the last page.

author: xavier60
author_rank: Super Contributor
timestamp: February 28, 2021, 05:37:42 am
content: Quote from: daisizhou on February 28, 2021, 04:51:57 amCan you post some internal photos?Are the battery contacts intact?

author: daisizhou
author_rank: Super Contributor
timestamp: February 28, 2021, 08:50:42 am
content: Yes, I have checked this model.They look alike, and the internal circuits are basically the sameThe only difference is the safety protection deviceI am trying to disassemble it

author: xavier60
author_rank: Super Contributor
timestamp: February 28, 2021, 10:29:44 am
content: 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,

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: March 01, 2021, 12:07:24 pm
content: 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 sitesIt 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