This one could be a bugger to track down. Do you have a scope? if so look at the output from your dac. If you don't swap the x and y inputs going to the scan amps and make sure there isn't anything wrong with your output. If that is fine and you have swapped the scanners and drivers and it follows the x card then there is probably something wrong with the x driver.
It looks like left side exhibits the problem more (could be just me). if it is more pronounced on one side there could be something wrong with an ic in either the -/+ rail, hence the worse output on one half.
Does it do it at rest? In other words does it do it if you are just projection a dot? Do you have a dc bias that you can use to just steer a dot to the left? Does it get worse the further left you go?
Chad
When the going gets weird, the weird turn pro.