Originally Posted by zac2613  Ha Ha Ha
I can see what you mean about bad eyesite, HarryGB ??????
Sorry LarryGB.....What a Plonker LOL |
Actually, I was referring to my bad eyesite
, but I have to "share that wealth" with you.
So, I've traced the 9Pin D Sub back to the PC board throught the Mini-Din Male and Female. The pin's in question according to the RS232 functions are Pin 1 [upper in your diagram] on Mini-Din is the RX lead, Pin 5 [lower in your diagram] is the Xmit lead. Of course the function on the meter will be reverse of that, i.e. RX to TX and TX to RX.
It may have something to do with the bias voltage on those pins, and how your skin resistance is pulling up or down the terminal voltages there.
I'm going to take a few voltage readings, and then play around with the scope and see if I can see anything unusual. Time to get out the resistance substitution box and experiment. Taking pictures as we go, so will post them when I have time....