Yep, RGB on seperate BNCs and H-V combined on another. I'm throwing a LeCroy scope onto the SYNC output and using the cursors to measure between the regular pulses. I pulled the graphics boardset and found one jumper (ext/int) that was set differently from Gerhard's model (thanks for the settings!) and I swapped that, which raised the sync frequency to 29.1 KHz. The total waveform looks like: 29.1-29.4 KHz negative-going pulses, with 134muS square negative pulses occuring at 66Hz (looks like it might be stuck in 33Hz interlaced mode). there are stronger negative pulses in line with the ~29 KHz sync at 400.96 Hz, and on top of that there are 174muS blanks in the signal (at the positive end) at 2.56 KHz -----\/---\/---\/---\/ (regular pulses) ---|_____|--- (vsync pulse, 66KHz) \/---------\ /---\/---\/ (the 2.56KHz blank and strong negative pulse) \/ not to time scale, and the strong negative pulse was the same duration as the regular horizontal pulses. The strong negative always occured after a blank, but not every blank. The Display Generator board is crystal-controlled (meaning I should have pulled it out all the way before pontificating) There is a set of jumpers on the main processor board (IP2) which are supposed to set resolution, with choices between 60Hz non-interlaced, 33Hz interlaced, RS-170A, and European Standard. These seem to make no difference. The jumper to select master/slave mode on the processor made a difference (dropped the sync to ~2KHz), so I know there is a control connection between the IP2 and the graphics. I checked the DIP switches, and they function. I suppose I could try the system with no processor and see what the default sync rate is. I'm wondering if the system (or parts) were set up for genlock of some sort, and is expecting something it's not getting. I'll throw the LeCroy on a Sun 3/160 and check the waveforms for comparison. Sorry, but you might need to "teach grandmother how to suck eggs", this is both the first computer video and the first scope I've really dug into. I found out really fast that my NTSC TV book doesn't help much. . .