RADIO SHACK/MICRONTA 22-195 Multimeter Calibration help

[santiniuk]

Hi folks.

I'm after some assistance. I recently found my first multimeter purchased some time ago. Its all working but could do with a calibration. It's got sentimental value.



I have found the schematic on

http://www.alfredpratt.com/tiki-view_blog_post.php?postId=72

As far as I can see the meter is built around a SMC4301F0A which I cannot find any datasheet for.

Looking at the schematic I can see pins 23, 24 and 25 have the references to VRF1 and 2. adjustable presets on here.

I have measured the voltages on the pins and stored these. A slight tweak to a preset does change the measured value.

I have a precision 5V external reference that was measuring 4.96V and I can tweak this to read 5.00V but I would prefer to know the correct method for calibration. I do have a lot of equipment at work available once I know the procedure.

Many thanks.

[Kryoclasm]

Wow, I don't think I have ever seen that one. It looks like a nice meter.

What year did you get it? How much did it cost?

[RacerX]

I have two of these myself...    have always liked them even though from "the shack"

It was Radio Shack's "flagship" unit in the late 80s, early 90s.

I still use mine even though I have much higher end meters now...   
solid unit has never given any trouble but I am also curious also about the calibration

[Fraser]

I bought one of these in 'as new' condition only a couple of years ago. No idea why, I just like it    My only complaint is that the digits are really skinny by todays standards 

Thanks for the link to a decent image of the schematic. Very useful.

[santiniuk]

Well it's good to hear others have this meter too. I must admit It's as good as new condition and I've just realised it's about 25 years old    My parents purchased it when I was a young lad hooked on electronics and even now with a lab full of equipment at work I'm still fond of this meter. It brings back memories walking around the UK version of Radio Shack (TANDY) and wondering what to save up for next.... Ah the memories.

I'm surprised so far no details of the SMC4301F0A I.C has turned up. The schematic is straight forward enough to see what to 'turn' to calibrate but I'm presuming some reference levels need to be set to complete the calibration.

Not looking too hopeful at the moment on calibration method which is unfortunate.

Thanks

[Andy F.]

Hello all,

I was looking for a user/owner manual and schematic for mine as well as calibration spec's and procedures myself. I found the manual and schematic at the links below. Manual is handy and schematics are poor quality, but they're free and helpful. I'm posting this for those who want them because the links above are either broken or not available anymore. None of these have the info or spec's to calibrate this meter, but still a great manual that explains usage and features in detail like they used to write 'em back in the day. Not like these cheesy skimpy manuals written today that are mostly BS for morons telling you you need an ac outlet and have to plug it into said wall outlet. 25 pages of BS and 1 page of actual useful info , ...if you're lucky. drives me absolutely crazy!

Btw... If anyone has a clear crisp schematic with spec's that are readable, I'd appreciate you being kind enough to please send a copy to me at AndysMailBag@gmail.com, thank you.


Anyway, here ya go...
MICRONTA 22-195 AUTO-RANGE Multimeter manuals and schematic links below.
These links are/were active as of this posting in Feb 2024 as I just found and used them myself.

ElektroTanya.com site you have to disable your add-blocker if you have one to get the download.

User/Owners Manual with so-so schematic: https://elektrotanya.com/micronta_22-195_auto-range_dmm_uses_smc4301f-04_owners_sch.pdf/download.html
A little better So-So Schematic only: https://elektrotanya.com/micronta_22-195_dmm_sch.pdf/download.html


Another is SCRIBD.com if you're a registered member. Over 170M documents available on just about everything, but you have to register as a member to download from this site.

User/Owner Manual with schematic: https://www.scribd.com/document/527765712/micronta-22-195-dvm-small


Repeater-Builder.com has the manual for free download. This is the site if you're into radio repeaters etc. This site has a ton of links to manufactures of various Amateur radio gear and related items for those who are interested.

Home page: https://www.repeater-builder.com/rbtip/index.html
Direct download link to the Micronta Mutimeter user manual pdf (Will not open a page. Instant pdf download to your PC): https://www.repeater-builder.com/radio-shack/22-195/micronta-22-195-dvm-small.pdf

[coromonadalix]

for the same chipset and better schematic    you had the 22-185A
https://manualzz.com/doc/22740038/micronta-22-185a-lcd-digital-multimeter-owner-s-manual
pdf included here


and you had this more modern variant,  chipset ?

22-175B

calibration ?
https://www.youtube.com/watch?app=desktop&v=8QKjevJc9VA