Thank-you to Dan for the link to the service manual scans, I never
would have figured this one out otherwise. I first replaced IC501
C1883CT, the H/V Control unit. It looked as if it had the identical
problem, excepts playing with the on screen controls I could now
almost stabilize the picture. Which means maybe I didn't just waste
$25. I carefully traced the vertical signal to Q401 which is used to
switch the v-sync on and off. Turns out the tiny surface-mount
transistor Q401 was also bad but tested OK with the standard diode
test. All-in-all a seemingly simple repair that turned out near
impossible.
(Nadir) wrote in message . com...
I have a Viewsonic P810 (Chassis 21HV8SA) monitor with a vertical sync
problem. Based upon some testing I have determined that the
vertical-sync may not be reaching the vertical output IC. I need the
pinout of connector N1002B, which connects the cable input daughter
board with the main board.

With no signal applied the "No Signal" test screen comes up clearly.
I can turn up the brightness on the flyback and see that the raster
fills the screen with no noticable distortion. However when I use
either the BNC or Dsub input, the video has no vertical hold. About
3 or 4 rapidly rolling images fill the screen. If I bring up the OSD
it sits in one place with only some flickering. The problem occurs at
all resolutions and refresh rates.

So far I have checked all the electrolytic caps in the vertical
section, none were bad. I then replaced the vertical IC490 (STV9379),
C409 (470nF, 100V Mylar) and C498 (56nF, 100V, Mylar). This had no
effect. I figure I may be able to bypass the mechanism which switches
between the d-sub and bnc inputs then I could isolate which component
is not passing the v-sync signal.

Any help is appreciated. Thanks