Fluke 187 Inaccurate Voltage/Backlight Button Issues

[Dback100]

Hi there, I've had this Fluke 187 for a while and finally figured to ask you experts for help. It works well except voltage is always reading high at the default 3 decimal range setting. If I manually set the range two 2 decimals or less, it's pretty spot on. If I set the dial setting to AC+DC Auto, it's also spot on. Any idea why the 3 decimal default is so far off? Photos attached.

Also, the backlight button has never worked for me, meaning it doesn't seem to do anything. I can't get the backlight on or get into any settings using it. The board and everything else looks pretty clean and these are more annoying issues than anything but it's bugged me for years. For what it's worth, I got it from a company surplus. Was this button disabled with software?

Thanks

Manny

[Dback100]

Pictures of the board

[M0HZH]

Are the readings stable or they're drifting? Are all the other ranges OK? Especially all three mV ranges need to be checked.

To me it sounds like the calibration for the 50V range is off. It's a nice accurate meter you should to send it to a cal lab in your area as they'll have the precision voltage source necessary to get it back to spec.

If you don't care about accuracy ... see calibration manual attached, you can reset to factory calibration. I advise against it.