Fluke 79 III manual range

[albert001]

Hello,

I recently purchased a used Fluke 79 Series III.

 The AC and DC voltage readings seem function ok. So far I haven't thoroughly tested other functions, most only DC.

However I noticed that there is no response from the "Range" button from any of the rotary dial functions.

When I press the "Hold" button "Manual" is briefly displayed from  upper left and then a "HOLD" is displayed upper right of the display.

 I replaced the Fluke 79 III 9 volt battery with a new one, still the range button doesn't want to respond from any of the rotary switch settings.

Earlier I did take the 79 III apart and removing the pcb (loosened small screw) and removed both fuses to inspect the circuit board  quality and design.

Then put everything back the same as it was.

From what I read from a manual when I press the range button the display should show "manual"?

While apart the range and hold  buttons fell out and I placed them back the same as before.

The internals of the meter are very clean. I didn't see an dust and  debris particles from the inside.

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Update:

I opened the Fluke 79 III and cleaned the button contacts (on the pcb and buttons) with a q-tip and some QD electronics  cleaner. Both buttons now seem to be working as expected.

So I guess the problem is only "dirty button contacts"?

Perhaps when I re-installed the buttons, skin oil got onto the button contact?