It sounds to me like you are experiencing a difference in potential between the GND connections between your computer LPT port and the machines PSU GND.
The LPT port’s pins 18-25 are GND and one of these pins must be connected to the laser PSU’s GND point (adjacent to the TTL(L) signal input as shown in my earlier diagram),
This should resolve the problem of the laser firing when it should be off.
Sadly, it does not... I went this morning and wired up the new board (pin7, pin25) gave it a test drive. BTW if anybody is interested, the TB6600 vs TB6560 believe it or not makes a HUGE difference in the sound of the machine. so much quieter now...
except for, it won't stop firing!
here are the details: it is wired exactly as in the diagram. before i was pulling the ground from the board, now it is soldered right to pin25.
what it does:
1) test fire button works just fine.
2) red laser led barely lights up when the laser control screw terminal is plugged in and goes out when unplugged. it brightens to full on when the test button is pressed. this is regardless of whether the pot is wired in or not and/or the setting of the pot.
3) laser is completely off until flood(relay) is on and then the tube sputters or flickers burning lines wherever it goes.
4) the only way to turn the laser off it to either unplug the screw terminal or to turn the pot down, in both cases of which the laser won't fire.
what I've tried:
1) two different computers
2) two different power supplies (i picked up this power supply because i thought there was a malfunction with the first which i bought used off ebay)
3) three different driver boards (expensive lessons learned!!!)
4) used pin 7 as both z direction and digital out
5) wired the power supply with and without potentiometer.
so if you have any advice or suggestions, that would be greatly appreciated. I am at a loss as to where to go from here. does the pin # make any difference? i am not to well versed in parallel ports and haven't used on since the days of the dot matrix printers; i'm a programmer not an engineer!
-derrick