Voltraft VC870

[Sebo]

Hello !

I have problem with this voltmeter VC870
All ranges auto/manual are ok, except when is on resistance (ohm) setting. Insted showing 0L, it shows 213,99 ohm. I tested every component and found nothing wrong. Sometimes, if you repeatedly short test leads a few times, it goes to autorange. Measure resitance ok except on lower ohm, then it shows again 213 ohm and stay there. If you short circuit test leads it shows 0 ohm, sometimes around 10-15. Manual range at kohm and higher is ok.
I have two of these VC870. I got them very cheap, i repaired one, this second gives me headaches ... When you press second function on ohm setting ( beeper ) it is also ok.
Both of multimeters on diode test position - test leads shorted, show 0.2470 V, which is also not normal. Must be zero. When measuring diode both show value higher, exactly +0.2470, compared to UT61E ...

ES51966A adc
AD737 rms-dc
MSP430 Mikrocontroller for display/data

Any help would be appreciated.
Sorry for my bad english.

[PKTKS]

Very frequently this little cheapos require care on the rotary switch
or whatever they use as such to change functions...

Cheapos and even some more expensive ones.
Those switches are a source of bizarre problems

Paul

[Sebo]

Thanks for reply !

The first one had problem with contacts on rotarity switch, i fixed that. The second one have more serious problem, i can not determine what...

[Sebo]

Hi !

Update

I have swapped eeprom from the second dmm. Now shows on the ohm range correct value 0L, before showed 213.99 ohm. Does anybody know fastest and easiest way to copy data from good eeprom to currupted one, or get new eeprom dump, or at least how to calibrate  these dmms because both have problem on diode function test, when short circuit tleads, they dont show 0 or near it, they show 0,24 V ...

[Sebo]

I removed eeprom from one dmm, works fine without it, i guess it i for store data and/or calibration.
But the problem on diode test remain, on both dmms. It still shows 0,24 V, when short circuited.
Voltage on test leads ( both dmms ) in this position is a little more than 4 V. Is this normal ?
On UT61E voltage is a little less than 3 V...