IBM 5151 (MDA display) - common faults / gotchas?

Hey, I had a question about this.. On Fri, Nov 7, 2014 at 11:49 PM, tony duell <ard at p850ug1.demon.co.uk> wrote: This is the same situation as the Osborne Vixen + Zenith 7" display. The display takes in a horiz. signal (a vert. as well, but that's another matter) which gets routed to a transistor, and then a 555 timer. From there, one more transistor and then comes the horiz. driver & opt. section. Anyway, the first two transistors and the 555 are collectively labeled "horizontal oscillator".. but that's not exactly the case, is it? I measured the horiz. input signal at roughly 16Khz; the chassis says it uses a 15.7Khz signal, so I assume that's the true freq. So if that's the case, it doesn't actually need an oscillator, does it? My guess was that the 555 was more of pulse-shaping deal.. it only uses the horiz. input as a trigger pulse, and then outputs a clean square / rectangle wave of whatever duty they want from the 555. That pulse then gets amplified. shaped, whatever by the next stage until it feeds the horiz. driver which in turn feeds the HOT. Is that what's going on in these monitors? @Jules I'm pretty sure I have one good-working 5151 monitor here, and just maybe a dead unit as well. If you need the worker as a reference, you're welcome to borrow it for as long as you require it to get yours repaired. Please just promise to be very careful with it.. ;-) And if I have it, the other one might be a parts donor should you need anything specific to the design, that you can't get off the shelf etc. Keep it in mind, for when we meet-up next spring or whenever.