pull up resistor on index question

[spiked3]

quick background;
I purchased one of these zero setters; http://cgi.ebay.com/ws/eBayISAPI.dll...m=270446538093

It works fine by itself, but I decided to put on a lug to attach an aligator clip to and use Mach3's index input for automatic Z zero setting. That worked fine on my old eMachine 600mhz computer.

Then I upgraded to a newer computer, a dell 2.8ghz Dual core. The computer itself works fine with Mach3. And on the diagnostic screen the above setup indicates good index signal. But, when I try to use the Z depth auto probing, it almost immediately detects a closed circuit, even though the Z barely moves. A little DVM check shows that the zero depth block is not really open, it shows a 300k resistance - but like I said it worked with the older computer. So it seems the parallel port electronics are a little different between the computers.

The question is; will a simple pull up resistor correct this problem? I'm not a wiz at electronics, but it would seem contrary to me. What would be a good value to try?

[japroach]

Do you have a breakout board? It should have pullups. Try using the DVM to measure voltage on the block, if it doesn't pop up to near 5V when open then try adding a 1 to 5k pull-up resistor.

If its quickly detecting a closed circuit on z-probe, but not staying on, it could be due to noise.