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Electronics => Repair => Topic started by: Amarbir[Lynx-India] on October 31, 2013, 04:17:28 pm

Title: Radio Shack - Micronta 22-206 Multimeter [ VOM Repairs ]
Post by: Amarbir[Lynx-India] on October 31, 2013, 04:17:28 pm
Hello ,
        Friends i have just imported one from USA to india  .The Unit and the probes are in mint condition but one of the resistances inside the unit is burnt of .Most of my measurements are wrong  .I am posting the pictures of the product in the thread .You can see the burnt resistance  .Can someone please assist me with a user/service manual or open his Micronta 22-206 VOM and let me know the value  .I tries a lot but could not find anything of our forums or the internet . :(

(http://i43.tinypic.com/xckuuo.jpg)

(http://i44.tinypic.com/2zr0yn9.jpg)

(http://i44.tinypic.com/2m60ewy.jpg)
Note :  The value printed under the resistance also was not readable due to burning of this resistance  .
Title: Re: Radio Shack - Micronta 22-206 Multimeter [ VOM Repairs ]
Post by: jucole on October 31, 2013, 05:06:27 pm
If the input circuit is the same as the 22-208, which can be found here...
http://elektrotanya.com/micronta_radio_schack_22-208_fet_vom_voltohm_mero_sm.pdf/download.html (http://elektrotanya.com/micronta_radio_schack_22-208_fet_vom_voltohm_mero_sm.pdf/download.html)

You are looking at a R20, 9.5 Ohms, 1/8 W +-1%
Title: Re: Radio Shack - Micronta 22-206 Multimeter [ VOM Repairs ]
Post by: Amarbir[Lynx-India] on October 31, 2013, 06:45:56 pm
Quote from: jucole on October 31, 2013, 05:06:27 pm
If the input circuit is the same as the 22-208, which can be found here...
http://elektrotanya.com/micronta_radio_schack_22-208_fet_vom_voltohm_mero_sm.pdf/download.html (http://elektrotanya.com/micronta_radio_schack_22-208_fet_vom_voltohm_mero_sm.pdf/download.html)

You are looking at a R20, 9.5 Ohms, 1/8 W +-1%

Hi ,
    Thanks for the support  .The value the current resistance is showing is 9.3 K Ohms  .I had a 10 Ohm  Resistance handy and i changed the same to that .The multimeter works very fine in all Ohms ranges and AC voltage Ranges  .The Amps Range is a little out  .But in the DC range as soon as i connect voltage to the meter the needle slams on the right side of the meter and remains there .I think if i can get user/service manual of this 22.206 meter i could then check all the components one by one and see if there is a issue in any .This made in korea product has very sensitive 25 micro amps meter movement thats smooth like butter .
Title: Re: Radio Shack - Micronta 22-206 Multimeter [ VOM Repairs ]
Post by: Whuffo on November 05, 2013, 12:21:34 pm
That brings back memories; I remember buying one of these new. It was a decent meter and served me well for a long, long time. I might still have it packed away in deep storage - I haven't seen it for a while. I retired it when I got my Fluke 79; the Micronta was still working last time I used it, but that's been a long, long time ago. You do understand that it's very, very old - right? I bought mine about 40 years ago.

The smoked resistor is a common failure - due to someone putting the probes across a voltage while the function switch was set to ohms. Be careful to replace them with the same type and value - close isn't close enough. This burned resistor only affects the ohms scale; if you have a problem with the voltage scales look elsewhere. My memory says it's a 10 ohm resistor - but don't take my word for it, it's been decades since I had to replace it in mine.

Make sure it's zeroed correctly. With the meter turned off, the pointer should rest on the zero line at the left of the dial. If not, adjust the plastic screw in the bottom of the meter (carefully) to correct it. Then, select a low ohms scale and turn the meter on - now adjust the "zero adj" knob to put the pointer on that zero line. Short the probes and adjust the "ohms adj" knob until it reads full scale.

For troubleshooting, remember that all the functions operate as simple resistive voltage dividers feeding a FET amplifier which drives the meter. Start by testing each selector switch position with a known test device and make notes of which scales work right and which do not. A pattern will emerge, which will show you where the problem lies.

When you get it fully working, you'll have a very good quality FET VOM that has high input impedance and gives accurate readings. It's a useful addition to any workbench and will serve the needs that digital meters don't handle quite so well.