Limit switch detection by Supercam

[greybeard]

At long last I'm in the process of setting up my newly finished router with SuperCam ver3.5T bought some years back, using an EMC-XYYZB controller unit.
I am in the middle of the set up, and on checking the limit switches, found that the Y axis limit switch does not change the on-screen indicator from OFF to ON in the "switches status" screen.
X and Z switches both work ok, and the +5v appears at the switch and then drops to 0v on engaging the switch. Swapping the cables makes no difference, and the Y2 socket gives the same result.
From this I conclude that the 5v supplies, the cables, and the switches are all OK.
I'm left with three possibilities - either I have a set up condition that is disabling the Y switch output, ie a software problem, or I may have a fault in the controller hardware, or a fault in the printer card in the pc.
I'm about to start checking the printer card, then I might try re-installing the software.
Is there anything else I haven't thought of ?

I have checked the printer port type, and changed it from ECP to SPP, but no change there.

I've emailed Dennis at Supertech, but if anyone else has any thoughts or suggestions I'm looking for all the help I can get
John

[greybeard]

The problem seems to be within the controller.
While the 5v appears on the input pins to the controller box, the output pins on the "parallel I/O" socket switch from 0.09v to 3.69v when the X or Z limit switches are operated, but the Y output stays at 0.9v.
I assume therefore that there must be an inverter/buffer stage between the switch input and the output socket, and this is where the problem lies.

Further investigation shows a 7414 type octal inverter, possibly wired up as four shmitt triggers(I think - it's been 50 years since I was doing this sort of thing !) for each of the four steppers, xyyz.
This feeds signals to a pair of 74LS244's and various and and nand gates, before the four L297 controller chips..
Help.

[greybeard]

I've emailed Dennis at Supertech, but if anyone else has any thoughts or suggestions I'm looking for all the help I can get
John

...and of course Dennis has come up with the goods.

With this model both Y axis limit switches need to be engaged, so a shorting clip on the non used input does the job.

Many thanks Dennis.
John