Ok, ran through the tests you outlined and here are my results:Originally Posted by jimbonzzz
- Got a new 9V battery, tested at 9.4V with no load; hooked it up to pin 7 of DB9 and ground
- Tested collector line from 3906 transistor, 0 voltage
- Tested base line, 4.3V (a bit lower than expected?)
- Jumpered a 22k resistor between the base and ground; base voltage changed to 4.18V
- Tested RXD (pin2) with jumper connected, shows 4.84V (with the 5% tol 4.7V zener in place)
Are there any specific COM port settings I should try? I left everything default in XP (9600b, 8n1, no flow control, default FIFO settings).