Fluke 845AB Needle Porn II

This is a follow-on to my previous video where I showed the unit with some new, random, neons in the photo-chopper circuit. Since then I've grabbed some that others on the EEVBlog (apologies for not remembering their names) had success with and I've now got a way less noisy meter.
Work still needs to be done though...

[@DrFrank-xj9bc]

Hi, there are still several things not right.. zero can not be "calibrated", there is probably an issue with the amplifier circuit, you need to check the waveforms and the supply voltages acc. to the manual. In my 845AR, I had to replace two electrolytics, which were dried out.
The needle should be much more stable in the 10µV range, even in 1µV, my unit shows much less noise (ok, the damping time constant is much higher there). I just checked: in the 10µV range, the needled slowly wanders +/- 2 divisons, or +/-400nV, in the 3µV and 1µV ranges it's as well +/- 2 divisions, i.e. about +/- 50nV
Have you checked the neon bulbs, whether they fire in the dark? If these new ones show the dark effect, then the noise is related to misfiring.
We had a detailed discussion on eevblog, identifying possible root causes.

[@tgsoapbox]

Thanks Dr. Frank - I believe the neons are working but I have not confirmed - They are certainly working more than the previous ones I had in there. I know you can't calibrate the zero but I was planning on doing that as a step before I started looking at further issues with the noise. Will review the EEVBlog thread.

[@TheDefpom]

Did you see my last 845AB video, just did the battery really and tested the power supply voltage etc, might be of help to check yours.

[@tgsoapbox]

Thanks Scott - I did watch your vids, you never replied to my question you bastard :) - As for the battery I replaced mine with some Tenergy NICADs to try and keep it original (though I suspect I'll need to move to the non-photochopper mod at some point and so I'll probably go your path then) - The noise dropped quite a bit between what I had before and now with the new neons - I'm hoping to ressurect it to working with old school components.

[@tgsoapbox]

I think I have an older one than yours (at least your knobs from memory as white where mine are darker - Did yours have the Neons or the newer chopper circuit?

[@TheDefpom]

@@tgsoapbox yeah mine is newer, might be some similarities though.

[@TheDefpom]

@@tgsoapbox keeping it original would certainly be nice. I don’t remember seeing your comment, sometimes I have found comments on videos that don’t show up in my notifications of comments list… (or filtered comments) it’s a bit odd.