Quote:
Originally Posted by old_coot88
Da-yum. You're sayin' that even with the CRT's G1 clamped to ground with a 10mf cap, the white bar remains unchanged? That means the bar is definitely not originating in the video chain (see how one quick test can eliminate or confirm a whole signal chain?  ). Does the bar roll if you turn the vert hold control or not? I'm gonna take a SWAG that the bar is locked to the vert sweep, in which case it will not roll. And another guess that the bar is actually appearing on the CRT's G2.. and that since G2 has boost voltage on it, something's allowing vertical pulse to get into the boost source.
Try this- do the ripple test thingy again with the .1cap, on the CRT's G2. I'll betcha there's some signifigant ripple there, causing the white bar.
Of course i could be completely wrong. 
The CRT appears to have a partial aquadag coating on it. Is that coating securely grounded? An ungrounded or poorly grounded 'dag can cause some really weird symptoms mimicking sync and AGC problems (a little factoid worth bookmarking). |
The white bars roll right along as I adjust the vertical hold out of lock, and back in place when I adjust the vertical into lock.
I'm not sure how much ripple would be needed to cause a symptom like that but G2 has in the neighborhood of 3VAC present on it without any signal injection.
The aquadag still looks intact and making connection to ground, looks can be decieving though I'm sure. Is there a good way to test it's connection to ground to rule it out?
What a mystery we have. Maybe it was the butler in the library with a pipe wrench?