Some seconds after I and Arnaud started the EX ESD TF measurement, EX PLL failed. VCO frequency readback was giving some nonsense numbers like 65MHz and such (should be about 79MHz), beat note was going around 0, PDH modulation readback was also nonsense, and we were even reading some frequency out of unused ports.

Daniel was suspicious about the DC regulator (7805) thermally overloaded, because that chip is without any heat sink (and, as it turned out, it was not even screwed down to the board itself).

We went to the EX, shut it down, and after a while powered it up again, and it read the frequencies fine. We pulled the unit, Daniel swapped the chip and put a heat sink on it, which unfortunately made it impossible to put the top lid of the chassis, but anyway we left it like that for the moment.

After putting it in the rack, it seems like it's working fine again.

Note that a proper modification should be made to this unit later, as well as all 3IFO and spare units.