toddpw@tybalt.caltech.edu (Todd P. Whitesel) (11/23/89)
I have an IBM 5272 monitor (color display for their 3270 computer) and have been trying to figure out what type of sync timing it needs. The "Maintenance Information" is written for morons and is totally useless except for one page (3-25) which gives the sync and video pins (i figured 1 and 2 are ground like the PC monitors seem to be) and I got video but it was torn and scrolling so I know both syncs are off. The video board I am using is an Apple //+ 80 column board, what's nice about it is that you can play with the 6845 directly and run it with any monitor you like. The standard firmware sets the timing to roughly NTSC (not really, it puts out 240 lines of video, I never worked out how much extra sync it throws in, but the Apple Monochrome takes it even though it takes up much more screen area than the strict NTSC non-interlace that the //+ puts out) and with an IBM-compatible mono amber it makes a stable picture but there were some odd effects that required minor position and width tweaking to fix. Starting with the default settings (I know what they are but it's easier to initialize the firmware and let it set them all) I increase the Vertical Total Adjust from 0 to $10 and I got what looked like a vertically stable picture but it was still tearing. After playing with the Horizontal Total and position I could not improve the tearing, and mostly made it worse. I didn't mess with the Horizontal sync width at all, that may be it; I want to learn more about these things so I can get more monitors up and running, especially a REAL RGB (not the TTL color like this 5272). Speaking of which, does anybody know the specs on a DEC VR241, it has separate coax for R/G/B/H/V and I can have one for free as long as I can show that I'm using it. Is there any algorithm for determining the sync timing of some given monitor? Or do you have to guess until someone finds the Tech Book? Right now I have a programmable mono display board, am planning to build a color display (bought the VRAMs already), have an IBM compatible amber which I can use, a 5272 color display which I currently can't use, and a possible VR241 which I don't have yet. Any and all info is deeply appreciated, if I knew where to look I wouldn't need to post. (If there are any video jocks out there please speak up and tell me what I could be dealing with. If my only hope is to call IBM, so be it, but I don't want to waste gobs of time finding someone who will look up the schematic for me since their Maintenance book has you Replace the Defective Component for half the symptoms. Thanx in advance Todd Whitesel toddpw @ tybalt.caltech.edu