Oh, Yes
.
This is just a quick diversion, to ascertain whether the monitor is at fault or whether the mainboard is failing to generate the sync signals. To cut the problem in half and see which half is good, and which bit bad, in effect.
Once we establish that it is the mainboard (if it is) then we'll take the usual sensible path, although that may depend to a certain extent upon how much time Pud is able to spare for sometimes exhausting and monotonous tests.
Certainly a check on the supplies would be sensible given the obvious rework which has been done in the regulator area.