Why does it work on a bread board, but not a proto-board?

[KC2UGV]

Ok, so this weekend, I spent the better part of working on a project that should have taken like 30 minutes.

It's a simple soundcard interface. Works fine on a breadboard, but when transferred to a protoboard, the rig stays keyed no matter what?

Basically, the DTR is connected to the base of a NPN transistor, with the collector wired to ground, and emitter wired to the PTT pin. Works FB on the breadboard, but when moved to a protoboard, and soldered, it keeps the rig keyed.

I've flipped the E-C connections around, same thing?

My serial port is -12V low, and 10V high. Any thoughts?

[WØTKX]

Did the transistor short out after installation or testing?

When weird things happen, I check the premise of my "grounds".
Spooky stuff can occur if there is a potential between them.

[KC2UGV]

Good advice. I pulled apart one of the last interfaces I built, and it appears I placed a blocking diode from ground to collector (As well as ground to most of the connections)...

Seem there was a reason for it... hehe. I've got to start a notebook on this stuff. My memories aren't what they used to be.

[W3WN]

Why does it work on a bread board, but not a proto-board?

Because boards do not work on bread alone?

[N8YX]

One thing to keep in mind regarding breadboards, especially at radio frequencies:

Inter-terminal capacitances - them'll git ya.

Effective capacitance between sections of the boards I've used has been on the order of 10-15pF. Trivial at audio frequencies; most assuredly not at, say, 20MHz and up.