repairing VT220 DEC terminal -

Not relevant to fxing the VT220, but IIRC, most DEC terminals with video inputs do not accept sync on said input. Instead, you haev to take the video _output_ signal from the terminal, extract the sync from that, and then lock your video source to that sync signal. Needless to say this makes such terminals not a particularly useful substitute for a monitor. It also probably explains what's going on here. They should be pretty simple. Monochrome raster monitors are all pretty similar, the differences are in the video drive circuitry (between the video input(s) and the CRT cathode). I would start y measurign the CRT electrode voltages It's difficult to state what they should bem but at least you'll see if any are missing, if the gun is biased way beyond cut-off (if the cathode is more than about 20V positive wrt the control grid), and so on, -tony