Hi everyone, this is my first post here.
Bit of a puzzle. For me, anyway. I have an HP 4957A that functions perfectly, with the exception that
the CRT does not show half-intensity video, which is a usability hassle because the smart key labels are shown at half-intensity. Interestingly this signal
does show up on an attached external monitor:

I have turned every potentiometer with no improvement.
Even at the highest contrast/brightness there is no sign of the half-intensity signal. It's just not there. Edit: Actually I misremembered. There is no apparent way to control brightness or contrast. The only pots are focus, vsize, and vpos.
I have also tried both the A0001 and A0002 ROM sets, with no evident change in behavior.
There doesn't seem to be a service manual out there anywhere and I'm really not sure where to look next. Any suggestions would be greatly appreciated. Thanks!
- rob