Need help for troubleshooting Excel DT-9205A multimeter

Thread Starter

planetElectron

Joined May 5, 2022
1
I'm just a starter.
I have a problem with Excel DT9205A meter and it is showing lesser ohm than real resistance in every range of ohm scale, only 96 ohm for 100 ohm, 968 ohm for 1k, 9.52k for 10k, 99.1k for 100k, etc., tested with 5% resistors.
I checked the series resistors of ohm scale with an analog meter (because I don't have another DMM) and all seem fine, and it has 100mV at the input of 10K resistor of main IC Ref+ pin, like described in the schematic, so it seems ok.
According to what I read, it seems Ref- voltage is getting less or Ref+ voltage is getting higher than normal. I checked componets (except capacitors) related to Ref+ and Ref- lines without removing from the board, and all seem fine, but the PTC thermistor connected at the input of VOhmDiode line, part code 4B DMZ, is unknown because I could not find that ptc code on the internet, also local stores don't have it and so I don't know its normal resistance, just tested by removing and heating with soldering iron and checking for resistance and it seems fine but not sure, I wonder if it gone less than rated value.
Can anybody help me to find the fault or tell me the normal value of the ptc if you have this model DMM?
Because my country is rather hot, please also take a note for the room temperature when you measure the ptc normal resistance, if you are not in an Air-Con room then °C shown in the weather app may be enough.
 

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Last edited:

DickCappels

Joined Aug 21, 2008
8,705
Well, everything has a tolerance. Your resistors are ±5% and your readings are coming off less than 5% off.

You might improve your understanding of the accuracy of your multimeter if you obtain some 1% or 0.1% resistors.
 
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