No where near MA, but I know a PLer that is, and he has a design lab with scopes.
Ok, differential means the input wiring to the amp from the ILDA connector uses both the normal and inverted signals for X and Y to drive the amp. Thus you have three wires to each amp input, X and X prime and Ground. Then Y and Y prime and ground. Differential is used to get the full drive for calibration.
I've found the 470 pF cap to be a critical component for stable amps.
OK, I'm 750 miles from my bench. We need to measure your position sensor "Volts per Degree". It could be done with a good DC voltmeter. I haven't measured it for my amps yet. I have not needed to.
Ok, This may/ will make your DT40 amp unstable and you may loose your tuning. Set up a small image, say the test grid, at 10 degrees or less of angle. While I never recommend changing position scale without an angle test rig, you should try it. Turn position scale about three full turns and see if the image size increases. If it increased, you should be at the correct end of the potentiometer travel. If it decreased, something is very wrong.
NOTE TO OTHERS READING THIS POST: Normal users should NEVER touch position scale after the galvo factory
has set the potentiometer. Doing so may cause you to loose your tuning and/or cause severe oscillation with certain images.
Steve
Qui habet Christos, habet Vitam!
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