Author Topic: Repairing a Micronta Multimeter -- Can't measure resistance, AC/DC is fine.  (Read 6194 times)

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Offline GiskardReventlov

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I'm finally getting around to looking into my micronta multimeter 22-203A, from 1981 I think. It suffered a battery leak and I think I cleaned up the residue and that's all fixed but now it won't measure resistance. AC/DC works fine.

Some pointers on what/where to poke and probe would be appreciated.

No it's not worth much but of course it's been around a long time and it's otherwise in good shape. I even found the receipt. Paid $31 for it in Santa Ana, CA.
 

Offline fluxcapacitor

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heres a manual,with schematic on the last page.

http://www.nl10609.nl/PDF/Micranta22-203Amanual.PDF
 

Online Flump

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iff all resistence ranges are dead checkout the ohms zeroing adjustment circuit (VR1)


I love old micronta meters , i have several myself  :-+
 

Offline calexanian

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we still have one of those models floating around the shop.
Charles Alexanian
Alex-Tronix Control Systems
 

Offline Joule Thief

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try cleaning the contacts on the A.Ohm / Voltage selection switch. I believe it is labeled V+ V- and A OHMS.

Perturb and observe.
 

Offline qno

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Check out the battery contacts.
Why spend money I don't have on things I don't need to impress people I don't like?
 

Offline GiskardReventlov

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@fluxcapacitor, thanks for the link, I've got the original manual still too.

I will check the battery contact, I thought I'd cleaned it up well enough.
Will look at VR1 and check contacts on V+-/A Ohms

 

Offline SeanB

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If the battery died a messy death then first off replace the wiring that connects the battery terminals with the board, it is very likely they are both corroded open. You will strip the end and find black copper or just sludge inside.
 

Offline GiskardReventlov

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If the battery died a messy death then first off replace the wiring that connects the battery terminals with the board, it is very likely they are both corroded open. You will strip the end and find black copper or just sludge inside.

Good point. Coincidentally I just fixed a battery powered pencil sharpener that was exactly as you described. I had to fashion a new terminal and replace the wiring.

I have had way too many batteries fail lately, I'm not sure why.  Maybe it's due to our quiescent Sun.
 

Offline SeanB

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I have done gate batteries recently where the rot got about half way down the cable. Luckily I have a lot of old airconditioner and microwave wiring looms that I have been using as wire with a built in right size spade connector. I even have different colours and connectors with 2 wires to feed to other circuits. Last battery had corroded itself to the terminal tight, so I had to cut the wire off down to the board end before finding clean copper.
 

Offline jancumps

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If you need some comparison measurements, I can help you. the one that helped me through my electronics studies in the mid 80s is still alive.

 

Offline pickle9000

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MMmMm, Radio Shack goodness. Mine was the 22-202, brushed aluminum 19.95, still have it, works, bought it new. I also have the dynamic transistor checker and a 22-220 FET I still use from time to time works really well.
 

Offline GiskardReventlov

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Ok, I think I got it working. I say "I think" because I barely know how to use a meter. It's always just been the basics. But since finding this site I have been going more in depth.

I used a 68k as measured by my BK  meter and then measured on the RS meter and adjusted to match. All's well.
But the Rx10k doesn't respond but I presume that's operator error. How can I test Rx10K setting?

The wire was corroded and so was the tab it connects to. Replaced the wire and cleaned up the tab. I had to solder the tab back into a single piece as it broke where it attaches to the wire terminal. This tab acts as a cam follower so it's springy and I had to tweak it a bit, i.e. bend it and check that it disengaged/engaged properly according to the cam position (the cam is connected to the selector knob).

The wire was corroded for 3-4 inches from the battery. Crappy battery!! Did I say I hate batteries sometimes?

Attached the receipt for this meter,  gas was about $1 then, so I paid 30 times what a gallon of gas cost.
My new BK meter is paid much less than 30 x gallon, closer to 20x.  What conclusions do we draw from this data?
Gas is too expensive of course!

Oh sales tax was 6% then and now it's 7-9%, it changes depending on what crooked county you're in, the bastards!
 

Offline GiskardReventlov

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If you need some comparison measurements, I can help you. the one that helped me through my electronics studies in the mid 80s is still alive.

Thanks for the offer, I'm using my BK meter to compare.  The cam follower I mentioned in previous post almost caused me to ask if someone could take a picture of theirs. But I think I got it right through some trial/error.

I wasn't sure if it went on the inner side or the outer side of the contact because the cam follower end broke off due to some corrosion.
 

Offline GiskardReventlov

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@pickle9000,

Great!  that catalog shows my meter for 24.95!!!  This is the worst, well ok maybe not the worst, but possibly the most delayed case of buyer's remorse on record.  32+ years!!



 

Offline 6E5

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Hi,

 I have the same meter here in the shop. I never use it, but it does have a nice big face. Unfortunately, I don't like how its cluttered with half a dozen scales.
 


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