H89 lives - but for how long?

From: Patrick Rigney <patrick_at_evocative.com>
Date: Wed Jan 14 15:34:14 2004

> >[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.

That's consistent with the troubleshooting guide. The supply voltages are 6
and 53 (regulated) for the video board IIRC, and easy enough to measure if
your fingers aren't too fat--it's tight in there. The assembly manual shows
the test points for power on and power off tests. But caveat, Jack: the
assembly manual I gave you is non-RFI, so those measurements may not apply
and/or test points moved. Interesting that it corrected itself, and I'm
wondering if it has happened again since? --Patrick
Received on Wed Jan 14 2004 - 15:34:14 GMT

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