Good day !
I bought a Fluke 8520a from EBay.
When I turn on the device, all is fine.
All the power rails are within the specs
When running the diagnostic program, on test sometimes fail. It's a VAC voltage gap but I don't think is related to my other main problem.
The unit seems to have two different routes for VDC reading (low and high voltage, controled by a relay). When the unit is in 100VDC resolution, the voltage displayed stays at 0 (or near). When it gets to lower resolution (10VDC or lower), the displayed voltage goes up (or down) by itself. Well pass beyond the reading limit of this resolution.
If I try to read the voltage at the VDC input posts with another multimeter, the input seems to de-energize and goes back to 0, then moves again.
When a VDC source is applied (10VDC) to the input, the reading is steady and accurate at every resolution. In that case, if I lower the input by the source, the voltage reading follows even at lower resolution, but if I unplug the source, the input stays energized and voltage reading goes up or down (still only at lower resolution, 100VDC res reading is fine). When I swap between the resolutions without a source, the reading resets.
I checked the Zeroing circuit TP that should pulse at InputVDC+2V and when the input energize itself slowly, the limit is 18,9VDC or so (pulse is there, but voltage too).
Since shorting the input de-energize it, I went with a multimeter and tested many TP, some were shorting the input too. Pass the DC buffer, I wasn't able to short the input.
Does anyone have experience with this instrument or have encountered the same problem?
Here is a vid (turn of the sound, I'm on an old chair)
https://1drv.ms/v/s!Aj0t8sj3fkXvja4NTQwfrTflZvu2tQ?e=hJdi0VI know that the manual warn for a ramp up but 18VDC? Is it normal?
My plan for now is to recap everything from the input to the end of the DC buffer. I'll keep you updated.
Thanks for your time!