[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Hits in CRT
I have a problem that has been driving us nuts here for a while. Of
course its an intermittent problem so it has been very elusive to
catch. We are getting 10 to 20 line "hits" in our CRT in our HD Rank.
These hits when captured on a still store or tape are just a drop in
luminance ( aprox. 10IRE in a bell shaped curve looking in the field
mode ) in positive and a bright up in negative, The picture is
completely in focus underneath the dim area and there is no geometric
distortion to any of the picture. This led us to belive that the
cathode or grid was having some problem. We have noticed that when
the Rank is cold that ( turned off for a while, or we bring down the
temp in the machine room) that these hits seem to appear once or
twice per 5 minutes. We have replaced: CRT's, High voltage PS, CRT
socket,CRT blanking, Backed down the High voltage to 25KV ( runs at
30KV normally ) removed the focus board, removed the pincushion board,
ran the back end of the CRT on its own independent supplies of
(filament, cathode and isolated the grid from the blanking signal)
replaced the scan rack frame ( not the cards ) replaced the main
power switch box ( beam current control ) and removed the rubber
insolaters in the Mc Murdos. The only thing left seems to be the
cradle or convince Dave Walker to make digital scans for High Def.
When you hang a scope on the grid or cathode you can not see any
disturbance. This one has me baffled. Any help would be appreciated.