Fluke 5100B drifting

[broketest]

Hello,
I have 5100B, who works perfectly, with action on pots on Ranging board etc. The Power supplies are stable. But the +10V from A14 is drifting after 5mn after power on. then the pots seems inactive, nothing moves.
I suspected U10 reference on A14 'SZA263), which i borrowed from a broke 8840A, unfortunately the restults are the same.
Does anyone have an hint?