Multimeter repair - final desicion?

[marekpasek]

Hello everybody,
I have a malfunctioned multimeter Metex m4650cr. I have created a thread about it already (https://www.eevblog.com/forum/repair/metex-m-4650cr-multimeter-repair/msg2804114/#msg2804114) and I got some interesting feedback. Check it out if you are interested.

To make long story short my unit has a constant deviation of 22% on all ranges of DC, AC, DV and AV. Other functions work correct with remarkably low offset after 25 years since calibration. The problem until now was that I could not find any service manual which would tell me what values the passive components in the unit should have and therefore I could not compare them with values I measured by another multimeter (my first assuption was that the deviation is caused by some burned resistor which messes up with some voltage divider ratio thus feeding wrong values into the ADC).

However, recently I found a service manual for a similar meter Metex m4650B. There are the values and the circuit shows some similarities with what I observed in the *cr model. Most importantly there is the low value resistor I found burned in my unit (discussed in the original thread). The value in *B model should be 1 ohm whereas I measured 2 ohm in my unit. Also in the service manual there are trimmers sorted by what range they trim.

So there comes the question. Do you think the low value resistor causes the problem? Should I replace it if it does? And would it also work if I just compensated for the deviation via the corresponding trimmer?

Thank you.

Service manual and picture attached below:

[iMo]

Why do you need two threads for the same repair?

[shakalnokturn]

It is quite annoying for forum database cluttering, future searching and general following of "a" subject.

[marekpasek]

Sorry for that. I am used to do that from other fora. In certain type of fora it is undesirable to make long conversation and vice versa it is appreciated if broad topics are "chopped" to shorter subtopics. Although it is important to note that it is common mainly in those fora where topics are listed by time of uploading, not by time of the last reply (the case of EEVBlog).