Fluke 8010a - AC not working [HELP]

[NZKiwi64]

Hi all,

long time reader first time poster.

I'm looking for some help with my Fluke 8010a - for some reason the AC measuring side is always reading overranger all the time. After consulting the manual, I've traced the problem to two things;

First is a zener diode (VR2) it splits supply voltage between pin 1 and 22 of U8 (RMS to DC) it's a 4.3v 1/2w zener - it's getting -13.6v and its output is -10.6v - (3.3v across the zener). Could this be causing issues with the U8 board?

Second If there is an issue on the U8 board it might be too much for me to fix (there is no schematic for that part - it's custom made by Fluke on a ceramic substrate.

Best beat for that would be to find a donor unit and swap U8 boards.

Let me know what you think or any thoughts you might have - I'd really like to keep this meter working.

Cheers