Radio Shack 2200813 29 range DVM

[Schoenradt]

Does anyone have any information for a Radio Shack 2200813 meter. I need to know what value R14 was. Mine is measuring 90 ohms. My meter did have a blown fuse F1 rated at 250V @ 500mA. Symptoms are meter doesn't measure DC mA correctly and beeps above 40 mA range if it is even giving proper current measurements. Below I have included some pictures and a macro shot of R14 on the pc board.

[eccerr0r]

Does the meter otherwise work on voltage, resistance modes?

Is that 90 ohms measured out of circuit?

What does the meter read if you pass 20mA in it with that 90 ohm resistor in it?

Without any additional information or schematic my guess is 10 ohms.

[stj]

show the whole board so we can see the chips

[Schoenradt]

Yes the other ranges seem to work. I don't see any way to zero the ohms out as the meter reads about 46.7 ohms when leads are shorted. I'll send some more pictures of the main motherboard and some LCD readings.

[Schoenradt]

Originally Posted by Schoenradt

Yes the other ranges seem to work. I don't see any way to zero the ohms out as the meter reads about 46.7 ohms when leads are shorted. I'll send some more pictures of the main motherboard and some LCD readings.

I have included photos of the main board and some tests using a known good meter and it isn't good.

[Schoenradt]

Originally Posted by Schoenradt

I have included photos of the main board and some tests using a known good meter and it isn't good.

Adding complete picture of main board component side.

[retiredcaps]

Originally Posted by Schoenradt

I don't see any way to ero the ohms out as the meter reads about 46.7 ohms when leads are shorted.

When you have an offset like that with the probes shorted, I would try the simple things first.

1. Try a fresh batteries first. Some meters give incorrect readings before they show a low battery indicator (if they even have one).

2. Give the entire PCB a good IPA clean with a clean toothbrush and let it dry overnight. Any unseen dirt, debris to the naked eye can affect the readings and give non zero ohms readings when the probes are shorted.

[redwire]

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.

[sam_sam_sam]

It could be the picture it self but I see some soldering joints that do not look very good I would check each and every soldering joint under a magnifying glass and reflow anything that does not look good

One other thing to be aware of is that meter leads have an issue with bad terminal connection issues and the meter leads that you get Radio Shack had these issues if you used the leads a lot

Or the wire that is used to make these meter leads are very poor quality and is corroding in the meter tip soldering joint or on the barrel end or both ends and will be either green or black in color on the wire strands bundle

Or the connectors pins on the barrel become loose in the mating connector spread them out a little bit and reinstall them and see if this makes any difference or not

However if the swivel is very loose and has play in it then this could also cause you problems as well it should be locked in place or if it rotates it should give you resistance to to move if not replace the barrel end with a new one

I have also seen where the barrel connectors corrosion inside the connector it self if that is case you can improve the connection by taking a piece of sandpaper roll tightly up that fits in the connector space and rotate it back and forth but note that if you have to do this then you are going to have this issue all the time

One more thing to be aware of is that if you have used this meter a lot the switch connections to the board can have corrosion on the traces or on the connection metal tabs that meets the board traces or not enough tension to the board end you can bend them outward however be very careful doing this because if you do to much of this can break them

I have a meter that has also done this as well but then some other failure issues happen to this meter and I stopped using it

I have 4 1/2 digit meter that has this issue can make you go mad because it a nice meter otherwise and it is the same problem with the meter barrel connector that becomes loose fitting in the connector and do not read the voltage or ohms correctly

I hope this helps