VM77E Range problems.

[stuart_morgan_64]

I have worked on this before, and had some advice too. It has now developed another fault, the mV ranges are fine but no reading on the V section.

I have a signal at R113. I have a reading on two volt ranges, 100V and 300V but very low, and don't respond much to adjusting input voltage, and read low.

The mV ranges seem ok. Put it aside for this evening, but will get back to it tomorrow morning.

Thanks

[Marconi_MPT4]

An interesting problem, have you made any progress so far?

While it has been raining today I lifted the cover on my VM77E and made a few signal measurements. Although not complicated there is a paucity of service information (*) for this model which makes diagnoses more of an effort.

With 1V range selected, an input of 2V pk-pk @1kHz will give approx 50mV pk-pk at C123 negative. The meter should indicate approximately 0dB and 1.6V DC measured on pin 6 of IC201.

(*) There are errors in the circuit diagram, Q204 is shown as PNP and R220 is shown as 383kΩ which is 383Ω in the production unit, confirmed by LTS simulation.

Rich