|Re: HP9100 CRT|
Message #2 Posted by Tony Duell on 7 Aug 2001, 6:27 p.m.,
in response to message #1 by Mark Sims
Firstly, DO NOT power that machine up. The electrodes in these CRTs are supported on (brittle) glass support rods. They break, and oyu get inter-electrode shorts. If you are unlucky, you blow transistors on the deflection boards, followed by diodes on the main gating board, and if you're _really_ unlucky, some of the flip-flop transistors as well.
To see just how bad it is, pull the CRT and the EHT generator fuse (on the PSU chassis). Power up, and try something that should result in an error (STOP, STOP, 1, CHS, SQRT is as good as anything). If the error lamp comes on, then the processor is basically working, and it's certainly worth looking for a new CRT. If not, then you have a processor fault to find as well.
OK, back to the CRT problem. It's HP custom (the main 'feature' being that it's very short for an electrostatic CRT). AFAIK, new ones are totally unobtainable now. Having the old one rebuilt is possible, although if it's been full of air for some time, the screen phosphor will need replacing as well, most likely. There are still a few companies who rebuild CRTs who _might_ be able to repair it, but I would think that the cathode/heater assembly would be
very difficult to get. I wonder if it's possible to interface an external CRT to the 9100 (without the modified deflection boards, etc that were used with the external display option). Tap off the signals from the deflection boards, and feed them to a simple 'scope or something. I suspect it would be cheaper than a rebuilt CRT.