MT2400 power graphing multimeter strange measurement problem

[R_G_B_]

I Have an automotive  power graphing multi meter with a problem:

It will not measure AC voltage or show AC signals on channel 1 when you select the AC measurement function.

However it does show AC signals when in other modes e.g if i go to the menu and select AC pulse generators then channel 1 will happily display AC signals.

Also Channel 1  has no problems displaying D.C signals and D.C measurements.

Note only channel 1 can measure AC signals. The rest of the meter seems to function OK.

The input coupling to this graphing multi meter is D.C on all channels. To get AC coupling requires an AC filter as shown in the link below:

I have tried to supply a pure A.C signal to the input channel 1 it will not read or show the signal when in AC measurement mode.

http://resources.aeswave.com/old/TechNotes/index1.htm


Could this be a firmware issue or corrupt data in the memory eeprom card?

R_G_B_

Thanks

[R_G_B_]

Selecting in the menu hardware and software test shows no problems with the hardware or software.

Also looking at the analogue circuit seems to use peak detecting analogue circuits.

Bit difficult to see where the fault is the meter functions in all other modes the only function that does not work is AC voltage over time which seems a bit odd. The graphing meter is directly coupled which implies both D.C  AC voltage share the same signal path for channel 1 of this graphing multimeter.

The signal is getting to the ADC as a waveform and the other channels of the ADC are receiving detected peaks of this waveform and when adjusting the amplitude of the function generator the signals at the ADC seem to follow the change in amplitude.