Keithley DMM7510 randomly shows Overflow at startup

[flo.b]

Hello,

I got a used DMM7510 which randomly shows Overflow on all ranges and most modes at startup and doesn't function, and the autocalibration fails with an error (I believe it was 2802, something with unexpected value, out of range).
Turning the device off, shaking and rotating it slightly, then turning it back on often helps and makes the unit fully functional again, including autocalibration passing.

There is most likely something loose inside, however I could not see or hear anything obvious after taking just the shell off.
All the connectors seem to be tight. The unit is very clean inside, it seems barely used, and never taken apart more than just the shell.
I wiggled around the PCIe-like board-to-board connector already (the one with optocouplers) which doesn't seem to have an effect.
The CR2032 backup battery was also replaced which didn't make a difference either.

The seller transported the device to me by car, he stated that this problem occured for the first time when he wanted to demonstrate the unit to me before buying. He seemed genuine, it was my choice to buy it.
After fiddling with the settings, he took the shell off, touched some cables on the side, put the unit back together and it suddenly worked.
The unit was bought by him in 2017, confirmed by a serial number check. The firmware seems to be the latest (1.7.12b), although it ends with "b" which could be beta?
I cannot download any firmware on tek.com, it wants me to complete my profile before downloading software which I tried many times with many different data, but it always wants me to start over again.
Could someone download 1.7.10 for me and upload it here? I was able to download it today and did a downgrade, just to make sure it's not SW related because the seller made the FW update recently.

Taking the whole thing apart is definitely not my first option, and I don't have special repair gloves at hand either.

Sending the unit in for repair will probably total above new unit price, so that's most likely not an option either.

I appreciate any help, thank you!

[coromonadalix]

it could be a simple input charging effect,  if it has very high impedance in the giga ohms ??

have you done simple tests / measurements ....


playing with firmware(s) is not always a good idea, since in the end the hardware still stay the same ?

if you start it up, with shorted input  what does it says ?

[flo.b]

If the Overflow appears at startup, it doesn't go away anymore and no tests / measurements are possible.
The unit has to be turned off and turned on again, then it might work normally, but not always.

Since it is so erratic, it might be a software issue. That's why I wanted to try to downgrade to 1.7.10.

Currently I cannot test starting it up with shorted input, because the Overflow message doesn't occur anymore.

[Kleinstein]

An erratic behaviour with sometimes working and sometimes not is usually not a SW issue, but like suspected from the start something like a poor contract of cold solder joint.

Especially if the meter is not running reliable and sometimes stopping it is not a good idea to do any SW update or downgrade - a malfunction during the update may cause more problems.