Hello Badcaps.netters,
I have a problem with a DMM, where there is a malfunction with the 4V measuring range, and the diode test function. The meter has a MAX134CMH ADC IC in a MQFP-44 pin format. See pinout diagram and schematic diagram of DMM circuit below.
When there is nothing being measured on the 4V range, pins 24-28 should be at 0V, but instead pin 24 has a voltage that alternates between 1.84V and 0V, and pin 25 has a steady 2.5V. Pin 24 is the input from the positive test probe lead, and pins 25-28 are connected to attenuator switches inside the chip, and to a resistor network externally. The 40V range and up all work OK.
I can only think that the presence of the voltages on pins 24 and 25 indicate that there is a fault within the ADC IC, and that replacing the IC should bring normal functioning to my meter. Am I correct in my thinking?
Cheers,
Krisby.
I have a problem with a DMM, where there is a malfunction with the 4V measuring range, and the diode test function. The meter has a MAX134CMH ADC IC in a MQFP-44 pin format. See pinout diagram and schematic diagram of DMM circuit below.
When there is nothing being measured on the 4V range, pins 24-28 should be at 0V, but instead pin 24 has a voltage that alternates between 1.84V and 0V, and pin 25 has a steady 2.5V. Pin 24 is the input from the positive test probe lead, and pins 25-28 are connected to attenuator switches inside the chip, and to a resistor network externally. The 40V range and up all work OK.
I can only think that the presence of the voltages on pins 24 and 25 indicate that there is a fault within the ADC IC, and that replacing the IC should bring normal functioning to my meter. Am I correct in my thinking?
Cheers,
Krisby.
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