"John Robertson" wrote in message
...
On 2017/07/04 5:44 PM, wrote:
ive got a tovis mtg-1901cn cga color monitor. in use, or with a test
pattern, the image starts out perfectly at the top. as you move down
toward the middle , it gradually starts to compress the image, with more
compression the closed you get to center. and when it gets to mid
screen, its a full vertical collapse. bright while line across the
center, with no image whatsoever in the lower 50% of the screen. also
sold as a vision pro .

battery voltage is good at 123, 12v and 24 v are good. 123 volts at the
flyback.
the vertical output ic is a LA7833. pin 6 has good 24 volt supply, and
pin 2 ( output) is a nice 24 v square wave. i recapped the monitor,
and the image is exactly the same. now im stuck.

thanks


Your vertical circuit is missing the bottom deflection half of the
vertical circuit. If the vertical driver is an IC, replace it, if it is a
pair of transistors then I would suspect the transistor pulling to ground
(typically the lower of the two on schematics) is the one at fault.

The vertical drive is just a very slow audio amp, apply audio amp service
methods.

Not quite - it has flyback boost and tailored feedback for linearity.

Either of those can cause similar symptoms.