Has anyone ever came accros this, I have repaired many of these AOC 7VLR monitors the ones with the round dial in front. The following problem on a whole bunch of them QTY 20+ (and counting) is that they start up perfectly fine and then after about 30min they slightly flicker and goes out of focus which only becomes worse. I have checked the Tube, Tube base board and lop T. It would seem logical that it could be the Lop T drive as both Focus and HT comes from here, but I have changed all the caps diodes etc, no luck. I have never came across this inland but now at he coast ehre the humidity is very high im faced with different faults. I have tried different approches on different monitors all with the same problem no luck it must be a common problem, the worse is I am now starting to see it on Mecer monitors as well??????
Any input apreciated.
I don't know the specific model but I have had the same experience with TV sets. One point 'may be' worth looking at is the actual tube base.
I have had build up of green verdigris on the actual terminals inside the tube base usually on the focus electrode, this could lead to intermittent focus or 'arc over' on the spark gap in the base.
If you look carefully the base is built in two halves, they can be a pain to open, you will usually find the focus terminal made of spring contacts.
I am not saying this is your problem but certainly worth thinking about seeing you have tried everything else... yet again I have had intermittent focus electrodes which meant a 'new tube' sometimes this fault cab be instigated by tapping the tube neck carefully.