Quote:
Originally Posted by SiriusHardware
Another left field suggestion - whatever it is is:-
-Periodic, but not synced to any other frequency in the monitor
-Of very short duration
-Powerful enough to disrupt the operation of indirectly related signal paths
Could this be something arcing - fault within the LOPT perhaps, or insulation breaking down across some other component or PCB path? Try getting the unit into a place of complete darkness, let your eyes adjust and see if you can actually see anything flashing over.
|
As noted in post 7 though, this disturbance it happening at about 5 times the vertical rate. Any sort of LOPT arcing/defect etc would happen at line rate or higher, meaning the disturbances would occur at least once on a scanned line and possibly multiple times along a scanned line, not across a field or frame. So it cannot be the LOPT or any signal the LOPT could produce being coupled into the signal circuits.
It is interesting how sharply and well all CRT beams turn off and on again for the short period of this defect. That makes me wonder if the aberrant signal is in the CRT's blanking circuits. But that theory would not easily explain why on a composite signal it loses color lock immediately afterwards, which suggests the power supply has a large glitch in its output. It would be very easy to solve with a scope.
The other interesting thing is how the time of the disturbance is only about one scanning line or two when it occurs across a frame and the amplitude of it is not disminished over time. For example if there was a coil somewhere ringing at 5 times the vertical rate after the vertical blanking interval, one might expect the disturbance to get less as the vertical scan progressed. So the defect almost looks like something you would expect if you injected a regular narrow rectangular pulse into the signal circuits. It will most likely be on the power supply rail, but there is always an off beat chance a sub-circuit has failed and is oscillating locked to the vertical rate, assuming those black lines are not rolling.