Hey- my buddy has a Nanao monitor that has some strange HV/brightness behavior.
At first, you see a bright white screen with some dark(er) vertically scrolling bands. Funny because when you adjust the screen control on the flyback, the scrolling areas change as if you were playing with the horizontal freq control.
If you turn the screen control WAY down, it looks like you lose the raster altogether, but not really- it's just that the screen gets dark and those bands are gone. Not a nice solid raster, but wavy on the sides and some odd artifacts.
Input signal doesn't matter.
So, as you turn up the screen control a bit, the screen gets brighter, and brighter until WHAP! It flashes white like a flashbulb and goes dark. It does this in a cycle- brighter until the flash, and then dark. If you keep turning the screen control up, the brighter/flash/dark cycle speeds up.
It keeps speeding up until you get the original behavior- what looks like a white screen with some bands of dark.
He just replaced the flyback and some caps. He says it was basically doing the same thing before. The B+ voltage looks right on (about 106.5V) and most of the static DC voltages from the schematic page are close.
I thought it might be some xray protection or shutdown circuit wigging out, but I don't really know.
Could something be shorted in the tube? Any way to tell without a rejuvenator? It's such an odd beast, I don't think we have a compatible tube laying around.
Thanks for any help.
At first, you see a bright white screen with some dark(er) vertically scrolling bands. Funny because when you adjust the screen control on the flyback, the scrolling areas change as if you were playing with the horizontal freq control.
If you turn the screen control WAY down, it looks like you lose the raster altogether, but not really- it's just that the screen gets dark and those bands are gone. Not a nice solid raster, but wavy on the sides and some odd artifacts.
Input signal doesn't matter.
So, as you turn up the screen control a bit, the screen gets brighter, and brighter until WHAP! It flashes white like a flashbulb and goes dark. It does this in a cycle- brighter until the flash, and then dark. If you keep turning the screen control up, the brighter/flash/dark cycle speeds up.
It keeps speeding up until you get the original behavior- what looks like a white screen with some bands of dark.
He just replaced the flyback and some caps. He says it was basically doing the same thing before. The B+ voltage looks right on (about 106.5V) and most of the static DC voltages from the schematic page are close.
I thought it might be some xray protection or shutdown circuit wigging out, but I don't really know.
Could something be shorted in the tube? Any way to tell without a rejuvenator? It's such an odd beast, I don't think we have a compatible tube laying around.
Thanks for any help.
