Zenith 19EC45 Vertical Problem?

[jblmar]

Had a look a the set toda and found the following,
Measured voltages to vertical board. All measured o.k.
With the back removed, the bottom of the screen remains black.
When I replaced the back panel, the picture clears up in about 15 minutes.
Remove the back and the problem is back!
Ajusted the vertical size (Vr 717). Screen size is now normal.

The problem is COLD related, not heat related. I'll ceck all the boards for cold solders.

Ron