When a Monitor II starts to exhibit a wavy display, it may be attributed to
overheating of the voltage regulator, IC601, mounted on the heat sink near the
power transformer. If a voltage check shows the voltage regulator to be good,
it may only fail while hot. Apple's Quality Assurance reports have indicated
that this failure is directly related to the mounting screw that secures the
voltage regulator to the heat sink. If the screw is loose, there is inadequate
heat transfer between the heat sink and the voltage regulator and it fails
prematurely.
When servicing the Monitor II, insure that the IC601 mounting screw is secured.
If you replace the IC601, be sure to use thermal compound or an insulator pad
(P/N 725-0006) between the IC601 and the heat sink.