Hi All.
I have a Micronta DMM model 22-185a. It was $50 to $60 some years back. So it shouldn't be total junk!
Recently, when I check DC voltages and I am looking for a "X.XXX" voltage reading, it won't range down to below "X." and I have it set on the correct range (I get whole numbers only with no decimals and inaccurate). The resistance testing seems to be working fine.
Does anyone have any experience with this who can offer some suggestions on how to knock it back into proper function? Maybe even know how to ensure it is calibrated properly and how to calibrate it if it is out? Or should I trash it?
I want a used HP LCR and a used HP DC/AC volt and amp meter, but I am waiting for decent deals on eBay. And the Fluke 289 is $500. I need to hit the lottery! LOL
Any help would be appreciated!
Regards//Keith
I have a Micronta DMM model 22-185a. It was $50 to $60 some years back. So it shouldn't be total junk!
Recently, when I check DC voltages and I am looking for a "X.XXX" voltage reading, it won't range down to below "X." and I have it set on the correct range (I get whole numbers only with no decimals and inaccurate). The resistance testing seems to be working fine.
Does anyone have any experience with this who can offer some suggestions on how to knock it back into proper function? Maybe even know how to ensure it is calibrated properly and how to calibrate it if it is out? Or should I trash it?
I want a used HP LCR and a used HP DC/AC volt and amp meter, but I am waiting for decent deals on eBay. And the Fluke 289 is $500. I need to hit the lottery! LOL
Any help would be appreciated!
Regards//Keith
if it's reading correctly on ohms, the ADC is working properly, could be that the resistor ladder for voltage has a bad resistor in it, or the range switching has a problem. there really are no calibration procedures that can help you here. i was a calibrator in the Army, and when we encountered a handheld DMM that was malfunctioning or out of spec, we NERTS'ed it (Not Economically Repairable This Shop) and ordered a new one. we were a Secondary Transfer shop, so were the highest level a DMM could go, and if we had to NERTS them, nobody could fix them. most handheld DMMs are permanently (thick film resistors printed directly on the PC board and laser trimmed) calibrated at the factory and there are no adjustments inside. Micronta DMMs, being made on the cheap are made to basically be throw-away meters. if you want, you could send it to me and i could send you a video of me shooting it with a .50BMG rifle
Hey unclejed613,
Do you have a Sloooooow Moooootion videooooo camera? That could be worth it and I'll save some of the "Sacred Fluid" (gasoline) with my motorcycle! Or maybe I should suffocate it in a plastic bag with duct tape!
Thanks for your response. Your experience makes your advice about the best I could expect!
I think you have it right with the range switch going bad. It was fine, then intermittent and then completely gone and I now have about 100 JFETs to test the Idss.
I am testing them with a 1K resistor and a 9-volt battery in series and measuring the voltage at both sides of the resistor for a mA value. That is why I need the value to go to 3 decimal places. Like 2.609 volts which would equal 2.609 mA in my test setup. All I am getting is 4 volts for all of them with no variation. I smell toast! (burnt toast)
Looks like I have to steal, gamble, etc. so I can buy what I need! What an expensive hobby!
Thanks for the help!
Regards//Keith
Do you have a Sloooooow Moooootion videooooo camera? That could be worth it and I'll save some of the "Sacred Fluid" (gasoline) with my motorcycle! Or maybe I should suffocate it in a plastic bag with duct tape!
Thanks for your response. Your experience makes your advice about the best I could expect!
I think you have it right with the range switch going bad. It was fine, then intermittent and then completely gone and I now have about 100 JFETs to test the Idss.
I am testing them with a 1K resistor and a 9-volt battery in series and measuring the voltage at both sides of the resistor for a mA value. That is why I need the value to go to 3 decimal places. Like 2.609 volts which would equal 2.609 mA in my test setup. All I am getting is 4 volts for all of them with no variation. I smell toast! (burnt toast)
Looks like I have to steal, gamble, etc. so I can buy what I need! What an expensive hobby!
Thanks for the help!
Regards//Keith
Hi unclejed613,
Yes, it is a rotary switch. I needed to be more clear when saying it wouldn't range down to the setting I needed. I should have been more clear and said it acts like it is on a higher voltage switch setting where decimals aren't used, even though the switch is on the selection for low voltage with 3 decimal places.
So maybe I can save you a heavy slug! (Is that a 50 calibre you were going to use to execute it? black powder? I hope you would offer a blindfold!)
I guess I should take it apart and clean the contacts. You suggest a pencil eraser but if the contacts are delicate, should I use De-Oxit or something like that?
Thanks for giving my little friend another chance at life! She needs to work to earn her keep! (like all of us!)
Regards//Keith
Yes, it is a rotary switch. I needed to be more clear when saying it wouldn't range down to the setting I needed. I should have been more clear and said it acts like it is on a higher voltage switch setting where decimals aren't used, even though the switch is on the selection for low voltage with 3 decimal places.
So maybe I can save you a heavy slug! (Is that a 50 calibre you were going to use to execute it? black powder? I hope you would offer a blindfold!)
I guess I should take it apart and clean the contacts. You suggest a pencil eraser but if the contacts are delicate, should I use De-Oxit or something like that?
Thanks for giving my little friend another chance at life! She needs to work to earn her keep! (like all of us!)
Regards//Keith
the contacts are most likely gold plated copper on a circuit board. they're not delicate. i've used pencil erasers on plated contacts for years, just don't use a gritty pen eraser on them.
that's not a black powder rifle i'm talking about. it's a .60BMG rifle. see pic below. this one is more fun than any human should be allowed to have. 
that's not a black powder rifle i'm talking about. it's a .60BMG rifle. see pic below. this one is more fun than any human should be allowed to have.
Attachments
Hey unclejed613,
Is that yours? What can you shoot with that, a Micronta DMM from a half mile? YIKES It looks like fun (with proper ear protection!).
Micronta DMM
So I borrowed a digital camera to show the kind of switches that are in my Micronta target! Do I un-assemble these by taking out the e-clip and then use an eraser on all contacts or do not un-assemble the switches and use a non-residue spray cleaner or a cleaner/lubricant? (see attached picture)
Thanks!
Regards//Keith
Is that yours? What can you shoot with that, a Micronta DMM from a half mile? YIKES It looks like fun (with proper ear protection!).
Micronta DMM
So I borrowed a digital camera to show the kind of switches that are in my Micronta target! Do I un-assemble these by taking out the e-clip and then use an eraser on all contacts or do not un-assemble the switches and use a non-residue spray cleaner or a cleaner/lubricant? (see attached picture)
Thanks!
Regards//Keith
Attachments
those switches are better than the ones i was describing.... use deoxit on those, and it might work like new. i was thinking of the switches etched onto the PC board and the knob having the leaf spring contacts on it. the ones in the pic are usually pretty reliable and will last a lot longer. cleaning those switches with deoxit should work just fine. the only thing that would NERTS those switches would be a bad case of corrosion with visible green crystals.
Oh well. it was worth a shot.
I spayed and clicked and sprayed and clicked. I can see the contacts and they are clean and fine. Maybe the center contact is bad on the lowest settings or maybe the resistors in the ladder just went? I am not sure which resistors are the ones for the lowest DC settings.
I look forward to any suggestions! Thanks!
Need to use a bullet?
Regards//Keith
I spayed and clicked and sprayed and clicked. I can see the contacts and they are clean and fine. Maybe the center contact is bad on the lowest settings or maybe the resistors in the ladder just went? I am not sure which resistors are the ones for the lowest DC settings.
I look forward to any suggestions! Thanks!
Need to use a bullet?
Regards//Keith
you might look at the pc board and see if it's cracked or if you have bad solder connnections. the resistors for the lowest ranges will be low value resistors (comparatively speaking, they are usually at least a few megohms), usually in meters they are all 1% or less tolerance. another thing that happens to DMM's (especially older ones) is damage to the input amplifier and ADC from static electricity. i once had a new Beckman DMM go south, just from the static picked up near the face of a TV picture tube. back then DMM's were a new thing, and DMMs were easily damaged by static. the problem has long since almost completely vanished as manufacturers have made the electronics in meters more durable. it is possible that your meter got damaged from exceeding the input voltage (marked in red between the banana plugs) limits if you have measured something that has a low average voltage but a very high peak voltage (like a horizontal output transistor collector on a TV or computer monitor, some of which might have an average voltage of about 200 or less volts, but peak values above 1500V).
So I got to the range selector switch again and put sonme 400 grit sand paper where I could clean the contacts. The switch will not come apart with it soldered into the PCB, even with the e-clip removed. Another blast of residue free contact cleaner.
While open, I checked evenything and the resistors, solder joints and PCB all look perfect.
I turned it on and the three lowest ranges worked again....... for a half hour and right back to the problem.
I knew exactly what to do and with the help of Chris (Anatech), I bought a new Agilent U1242A. Probably one of the best values around for a DMM. He assured me it was the one to get at this price range ($220.00 USD).
I got it yesterday and It is an investment. Truly impressive. Check it out.
Now if only someone can tell me where I can still buy that rotary switch for my Micronta POS.
Back to measuring Idss!
Regards//Keith
While open, I checked evenything and the resistors, solder joints and PCB all look perfect.
I turned it on and the three lowest ranges worked again....... for a half hour and right back to the problem.
I knew exactly what to do and with the help of Chris (Anatech), I bought a new Agilent U1242A. Probably one of the best values around for a DMM. He assured me it was the one to get at this price range ($220.00 USD).
I got it yesterday and It is an investment. Truly impressive. Check it out.
Now if only someone can tell me where I can still buy that rotary switch for my Micronta POS.
Back to measuring Idss!
Regards//Keith
while those switches are far better than most used on cheap DMMs, they do have their limitations..... if the silver plating was worn off the contacts to begin with, you didn't hurt anything using sandpaper on them. the copper does have a tendency to oxidize quickly. there is a better way to burnish switch contacts (and relay contacts) and that's with a piece of brown paper from a paper bag. glad you bought a new DMM you're happy with. i have an old milsurp Fluke handheld i'm happy with, and also hace a couple of odd cheapo meters i keep for things like working on the car, etc...
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