Wells Gardner monitor problems

[RonKZ650]

Wells Gardner 27" industrial monitors used in bowling alleys model 27K3003
built in 1996. I do service on these various monitors for about 10 different
bowling alleys around the Denver area. The problem I'm having is confined to
only one bowling alley. The monitor will come on with a bright white raster, I
find all 3 video outputs shorted. I replace all 3, turn on the monitor, see a
perfect screen. Problem is this perfect screen will return to a bright raster
with all 3 video outputs shorted again within a few days. The monitor plays
perfect, all voltages perfect, grounds all intact, tapping on the neck of the
tube and running a screwdriver around the anode cap and flyback, I cannot make
the tube arc in any way. These use good RCA tubes. I now have this condition on
3 of this alleys monitors and the alley only has about 14 lanes. Any ideas
besides a rash of bad CRTs?
Thanks, Ron Hansen

 

[Jerry Greenberg]

The only thing I can see happening here, is that the CRT is doing an
internal arc, thus causing an overvoltage to the video output drive
transistors.

Or, there is an intermittant overvoltage getting to these transistors
somehow.

Jerry G.
http://www.zoom-one.com

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