Hello badcaps.net Forum People,
I have a Protek 506 DMM which has a problem with the Diode Test Function and with the 4V range of the Voltage Measuring Function. I have posted this on three other forums, but have not been able to find out the source of the problem.
It seems that the Diode Test problem is linked with the 4V range Voltage Measuring problem, so I shall just focus on the 4VDC range to simplify things.
When I select the DC voltage function on the rotary switch of this DMM, the display alternates between showing 3.999V and 0V. If I test a 1.5V cell, the display alternates between 3.999V and 1.5V. If I test a 9V battery, the display shows a steady 9V. So that indicates to me that the fault is with the 4V range.
The Diode Test Function is stuck on displaying the word "OPEN" and the accompanying voltage of "3.999V". It should be showing 3V or less, which is the voltage used to do the diode test with.
I've checked out the components leading up to the A/D Converter IC, which is a MAX314CMH, in a MQFP-44 case (Metric Quad Flat Pack 44 pins). So it seems like the fault may lie within this A/D Converter IC. I have attached the data sheet for the MAX134, the schematic diagram of the Protek 506, and a pin configuration diagram for the MQFP-44 version of the IC, because it is not shown on the datasheet.
My limited understanding of this IC is that the ranges are determined via attenuator switches inside, which are linked to an external resistor network at pins 25-28 (RN1 on the DMM schematic diagram), and the voltage to be measured entering the IC at pin 24. When there is no voltage to be tested at the probes, pins 24 to 28 should all be reading 0V. However, I find the following voltages:
pin 24: 1.85V and 0V alternating
pin 25: 2.95V
pin 26: 0V
pin 27: 0V
pin 28: 0V
So, I am wondering if the problems I am experiencing are caused by a fault in the MAX134 A/D Converter IC (U2 on schematic diagram) or in the microcontroller (U1) that tells the ADC what to do, or some other componentry on the board?
Any ideas?
I have a Protek 506 DMM which has a problem with the Diode Test Function and with the 4V range of the Voltage Measuring Function. I have posted this on three other forums, but have not been able to find out the source of the problem.
It seems that the Diode Test problem is linked with the 4V range Voltage Measuring problem, so I shall just focus on the 4VDC range to simplify things.
When I select the DC voltage function on the rotary switch of this DMM, the display alternates between showing 3.999V and 0V. If I test a 1.5V cell, the display alternates between 3.999V and 1.5V. If I test a 9V battery, the display shows a steady 9V. So that indicates to me that the fault is with the 4V range.
The Diode Test Function is stuck on displaying the word "OPEN" and the accompanying voltage of "3.999V". It should be showing 3V or less, which is the voltage used to do the diode test with.
I've checked out the components leading up to the A/D Converter IC, which is a MAX314CMH, in a MQFP-44 case (Metric Quad Flat Pack 44 pins). So it seems like the fault may lie within this A/D Converter IC. I have attached the data sheet for the MAX134, the schematic diagram of the Protek 506, and a pin configuration diagram for the MQFP-44 version of the IC, because it is not shown on the datasheet.
My limited understanding of this IC is that the ranges are determined via attenuator switches inside, which are linked to an external resistor network at pins 25-28 (RN1 on the DMM schematic diagram), and the voltage to be measured entering the IC at pin 24. When there is no voltage to be tested at the probes, pins 24 to 28 should all be reading 0V. However, I find the following voltages:
pin 24: 1.85V and 0V alternating
pin 25: 2.95V
pin 26: 0V
pin 27: 0V
pin 28: 0V
So, I am wondering if the problems I am experiencing are caused by a fault in the MAX134 A/D Converter IC (U2 on schematic diagram) or in the microcontroller (U1) that tells the ADC what to do, or some other componentry on the board?
Any ideas?
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