开云体育

Hello,

I purchased a non working CD V-720, and found the meter "nuts" were not present which caused the meter to not show any movement...obviously. After connecting the meter, it seemed to be ok enough to zero, but..... most ranges were maxed out which I take as high leakage current from something dirty. The insides looked pretty clean compared to others with battery leakage damage.

I removed the chamber and the leakage currents were reduced to a ~0.5R/hr reading on the 1x scale. I cleaned the glass insulators on the chamber with 99% IPA and a Qtip and the chamber leakage went down to about 12 R/Hr on the 10x range.

Looking at the schematics, I see mine is different from what was published in 1961. I have a 8.2k resistor across the meter, and the 470k resistor near the potentiometer is 100K ohms. I am wondering if they made changes in 1971 when a faint stamp shows CD calibrated the meter. It looks like my meter was made in 1962 with "62" on the meter and a 62 date code on the vacuum tube.

I scraped off the flux residue on the solder side of the PCB (kept dry), and that sorda helped, bringing the 1x leakage currents to show ~0.25 R/hr on the 1x scale.

I am thinking the glass insulators are still dirty which is causing the upscale readings, and there is a leakage path on the PCB or switch somewhere.

Questions:

What was the 470K -> 100K resistor mod supposed to do?

What is the resistor across the meter for?

Does this meter require a desiccant in the can to help reduce the upscale readings?

Thanks for any help, I attached the check results with and without the chamber, name plate and? one of the component side. I left them full resolution such that one can zoom in if need be.

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