14 Jan
2004
14 Jan
'04
3:34 p.m.
[Jack Rubin:]
Here's my question - after the machine was running for a minute or so,
the screen got very bright - the "black" background became green and the
screen characters were so over-driven that they became "fuzzy". The
brightness control worked (i.e. changed brightness levels) but the
available range only went from "too bright" to "really too bright".
After another minute or so, the brightness level gradually subsided back
to normal and everything seemed ok for the next 20 minutes of operation.
What caused the "glow" and what incipient failure does it suggest?
[Joe:]
I've never worked on a H-89 but it sounds like the power supply that's
supplying power to the video display is losing it's regulation. Check the
12 VDC or whatever supplies power to the video display. I'm sure that
you'll find that it's voltage is increasing at the same time that the
screen blooms.