Advice for Tek 4051 vector-drawing issue?

Josh Dersch wrote: If the endpoints are correct, then the DACs are probably OK. That leaves the deflection system, and the two filters (one X, one Y). Take a look at 2-12 (#81 of 228) from service manual volume 2. To rule out deflection, I'd get an oscilloscope (a Tek 454 or similar should be more than enough), set it to X-Y (Lissajous) mode, and wire it up to the X and Y signal outputs from the filters -- there are two test points shown on the schematic for this (TP X and TP Y). If the display on your scope is still non-linear, go looking for faults in the display filters. If the display looks good on the scope, I'd start looking for issues in the CRT deflection circuitry. If you're going to hook it up to a scope, I'd try and get it to produce an alignment pattern that checks 45-degree lines drawn "both ways" so to speak. Either something like the Atari Asteroids self-test pattern, or even just a cross inside a square. Maybe something like this? 110 MOVE 0,0 # draw square forwds 120 DRAW 0,100 130 DRAW 100,100 140 DRAW 100,0 150 DRAW 0,0 # X forward-slash 160 DRAW 100,100 170 DRAW 0,0 # X back-slash 180 MOVE 0,100 190 DRAW 100,0 200 DRAW 0,100 # draw square backwards 210 DRAW 0,0 220 DRAW 100,0 230 DRAW 100,100 240 DRAW 0,100 # back to the start 250 GO TO 110 That's assuming the syntax of the DRAW command is "DRAW x,y", 0,0 is the bottom-left co-ordinate, and 100,100 is the top-right... The idea of this is that you can tell at-a-glance if the vectors are converging properly in both directions in all axes. -- Phil. classiccmp at philpem.me.uk http://www.philpem.me.uk/