Commodore 1084s-D1 High-pitch whine FIXED!

[F0LLETT]

Have you checked, line drive transistor. Which basically drives the LOPT.
They normally go short and can cause the effect your getting.

Regardless of being a monitor. Its basically a TV (just no tuner).

[F0LLETT]

Thats better.

Seeing pic of board helps. Nice you found short.
Would be worth once you get parts, check for dry joints. I can see D224 has a nasty dry joint on one side.

Miss the days of faults, being just dry joints, . Judging by pic there are a few.

[F0LLETT]

I've ordered 4.7uF 100v electrolytic non-polarised.

Ouch, I would not have turned it on, until had replacement parts. You may have caused more damage.
Looking at small parts of the manual doesnt help. Where it 4.7uF located?

Edit: Nevermind I see it, around the Horizontal Drive circuit.