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Old 10-17-2021, 11:38 PM   #8
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Join Date: Dec 2010
City & State: Alberta
My Country: Canada
Posts: 2,464
Default Re: Radio Shack 2200813 29 range DVM

Strange it has only one switch position for the mA/A function, so the shunt R14 is very likely 1R. 99R is typically used for a uA function.
RAA1, RAA2 give 10R but there's no switch position to use them? some of the resistors appear to be loads for the battery test function.

It looks like earlier Dream Tech Taiwan DMM IC used and a COB LCD driver.
DTL02001 but I could not find a datasheet. Very similar to the ubiquitous DTM0660L. The multimeter's right part number is Radio Shack 22-813 similar to 22-812 etc.

I would check voltage regulator U3 is 3.0-3.6V output across C7. You should get half its voltage between BATT(-) and input jack COM.
The voltage reference is across C2 and I believe 1.2V
Maybe measure these in the DCV function to see if the IC has hope.
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