Extech MN35 DMM problem...

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#21
1. 200ohm probes shorted,,, 8.8.8 fluctuating to 8.8.4 and 8.8.5
2. 1K resistor reads,,, 1.8.8.8
3. -18.8.0 with the minus sign and one flashing on and off
Thanks for all the info,,, I will try to back light the PCB and trace those resistors...
 
#22
Oh my. On manual-range basic meters like this the decimal points are simply controlled by a section of the switch. Very odd that more than one would be on at a time, so not good. When you get a chance, with the meter on, check the voltage between the COM jack and the positive battery terminal. It should be close to 3.0V.
 
#24
mrmodemhead said:
Oh my. On manual-range basic meters like this the decimal points are simply controlled by a section of the switch. Very odd that more than one would be on at a time, so not good. When you get a chance, with the meter on, check the voltage between the COM jack and the positive battery terminal. It should be close to 3.0V.
Click to expand...

Not always but usually yes. Either way, this indicates something is horribly horribly wrong with this meter. Much more than just the damaged resistors. I am betting the main IC is toast, not surprising.
 
#25
One of the basic functions of an x7106 is to regulate the voltage on its COM pin with respect to its V+ pin. The original Intersil ICL7106 specifies 2.8V, but the Chinese clones are usually closer to 3.0V. If this isn't happening, then either the makers of this meter went with an odd design, or the chip-on-board (black blob) is toasted.
 
#27
knockbill said:
OK,,, well at least we tried... I guess there is really no way to read it out without a schematic...
Click to expand...
Well there are a lot of similarities in inexpensive DMMs based on x7106 clones, so it's not impossible to make a few assumptions and maybe figure some things out. There are endless circuit variations and PCB layouts though. I did notice that the makers of this one kindly included some pin numbers from the original 40-pin DIP ICL7106 in their silk-screen. That's where the "25", "26", "COM", and "35" come from.
 
#29
knockbill said:
Thanks!!
Here ya go,,, The 3 resistors are along the top edge of the pic, arranged vertically about 1/2" to the right of the yellow hold button, and 1/2' above the blue cap...R15 is next to the edge,,, these resistors look burned, the numbers are no longer legible...
I'm assuming they are open, the meter I checked them with has a 2M max ohm scale...
Click to expand...
Hola amigo yo tengo el numero de esas resistencias yo necesito el numero de la R28

Hello friend I have the number of those resistors I need the number of the R28
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:cop: please add an English tranlation when posting in another language.
Por favor, añada una traducción al Inglés la hora de escribir en otro idioma. (google translate).
 
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