IR probe & Digitrace questions

mikeymike · Post by **mikeymike** » Wed Mar 07, 2007 4:31 pm

theoretically,, i shouldnt have gotten voltage on all 3, i realize that. i think it may be best for me to cannibalize one of my old printer cables, identify each bare wire with a continuity tester, and the start taking readings from that. i can also check for continuity between the chassis and pin 25.
whatevere the problem is here was no doubt the reason that the probe didnt work with digitrace as well

johnsfine · Post by **johnsfine** » Wed Mar 07, 2007 6:11 pm

Why can't you test voltage right at the connector on the back of the computer, without a cable?

But anyway, you could easily have + voltage on all three pins if pin 25 wasn't connected or if the wire in your probe cable that you thought was pin 25 was really some other pin.

I think my suggestion of checking which of 18 through 25 is ground, is your best path forward.

Ctrl-G · Post by **Ctrl-G** » Sat Mar 10, 2007 3:16 pm

I remember I was having similar issues in getting the probe to work .. sorry I don't remember the EXACT details of my testing as this was several months ago. Regardless, after breaking out a power supply, a digital logic probe that I made in p.c. board class and my DMM I surmised that the pin 9 was not floating high enough to be considered a logic 1 signal by the Parallel port.

I ended up putting a 2200 ohm 1/4 watt resister between pins 1 and 9 in the DB-25 and everything came to life.

Now it works great.

Hope this helps,
Bruce

mikeymike · Post by **mikeymike** » Sat Mar 10, 2007 3:26 pm

thanks for the info ctrl-g, i will keep that in mind. i havent been able to work on it the last couple days,, weekends are busy for me, but tomorrow,, hopefully i will be able to figure this out.
thanks,
mike

Ctrl-G · Post by **Ctrl-G** » Sat Mar 10, 2007 3:36 pm

Well then again .. if you are getting 4.35 volts on Pin 25 .. my suggestions may provide very little help indeed. You are going to HAVE to have a good ground point for this to work .. I don't know what you are using as the ground point for your meter .. but you could always remove the wire to pin 25) and then connect that wire to where ever you have the meter's ground lead connected while everything else is connected as before and see if that works. If it does ... you know somethings weird with the Parallel port.

Just a thought & good luck,
Bruce