Meratronik V543 Voltmeter

[mldevw]

Hi,

on the plus side I just aquired an old nixie voltmeter from Meratronik with good documentation.

Now I figured it has a offset of about 160 mV in the 10 V measurment range,but I can't calibrate it, as the total potentiometer travel only does a 10 mV change.
I also tried calibrating the 1V range there is only a 5 mV difference but changing the potentiometer does absolutely nothing there.
(Yes, I made sure to warm it up and turn the right potentiometers, according to documentation).

Anyone had this fault before?
What point can I start analysing the issue?

Thanks in advance.

[doktor pyta]

Please tell us readings for shorted input. Go through all DCV ranges.
We must distinguish zero error (offset) from gain error (slope).

10-turn potentiometer on the front panel 'zero' can have dirty wiper contact.
You can test it using ohmmeter.

You can do simple test - remove DC amplifier board and short it's output to ground (LO).
You should get stable  zero reading unless there is a fault in AD converter board.

P.S. I have a calibrated V543 but in other location.
If You won't solve the problem I can measure some voltages in the circuit for You - to have the reference.

P.S.2. Manual is there: https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwjJmYiT_4jvAhVlkIsKHQjKCS0QFjAAegQIAhAD&url=http%3A%2F%2Fbee.mif.pg.gda.pl%2Fciasteczkowypotwor%2FPolskie%2520mierniki%2FV543_2.pdf&usg=AOvVaw0wWdLV4loh_KVyHdZhIFXc

[bob91343]

A circuit diagram certainly would help.

[coromonadalix]

what  i've found,  a djvu file  converted to pdf

from :  http://multimetry.tzok.eu/multimetr.php?typ=V543

[bob91343]

Always check the power supply first.  Voltages and ripple.

[mldevw]

Hello,

unfortuanetly I currently can't work on it, but I figured it is a slope error.
I will try to take out the DC amp board to check if there is a fault on the AD converter;
My zero potentiometer is fine.

Thanks a lot.