I've had the RAMPS/MEGA combo up and running for a couple weeks now.

Clearly the problem was the Sanguino as things just worked once I had the everything put back together with the new board.

I wonder what would happen if you swap your good drivers into the y driver slot?

I swapped drivers (the driver is fine).
I swapped stepper wires (the wires/motors are fine).
I swapped PINS on the ATMega (PINS are fine)
I swapped the resistor, and capacitor (those are fine).

The only questionable solders I saw were my own on the replaced resistor and capacitor and I redid those better...no difference.

Thanks all for the suggestions.

I ordered a Ramps 1.4 / Mega 2560 combo today, though it would have been nice to isolate the problem with the Sanguino, I feel I made a good effort to fix what I had before spending the money on an upgraded board.

Did you end up checking for dry solder conditions on the back of the board?  This happened to me on another piece of equipment...sometimes very difficult to see.

Yeah, I have seen this many a time on older televisions, usually in the hi frequency circuit.

very strange... I thought for sure you would find something while wiggling plugs around.... been too busy aat work to have much time to actually do anything with my spare board... maybe this weekend

I also did as you suggested ronsii and pushed/pried on the board & plugs while the monitor was turning.

I also checked the voltage during this operation and it fluctuates +/- .005v, which I don't imagine makes a difference here, but this is something different than the other stepper drivers which only vary .001v generally.

So at this point I'm contemplating upgrading to a Ramps 1.4 / Mega 2560 combo.

So I've now ruled out:
- The stepper motor, wire, and connector
- The driver
- The microprocessor

Here's what I think is left:
- The resistor
- The capacitor
- The PCB (perhaps dry solder)

Anything I'm missing in this list?

Your connections to the motor maybe intermittent and/or it is only driving one coil. It wouldn't hurt to take a small flat blade screw driver and try to "recrimp" the wires in the connector for that motor.

It's not the motor as I swapped the Z and Y leads and the Y motor worked fine.

It's also not the driver as I swapped those.

It's something on the board.

you could probably check them in circuit with moderate results.... if you check the resistor and it's open or a lot higher ohms than it's supposed to be of course it's bad same with the cap if it shows a short it's probably bad... I kinda doubt it's this though...

I checked both the resistor and cap relative to each of the steppers and am getting consistent measurements across them.  They also look fine physically.  So they seem OK, and now I'm at a loss for what to check/try next :-/

Other things it may be is metal debris on the back side of the main board... it wouldn't be the first time an errant piece of tiny wire trim was causing problems on the back of a SD printer board....

That happened to me once, piece of tiny wire on my stepper driver... I guess everyone's workshop is the same.

I didn't remove the reset jumper when I first installed the chip and I'm guessing it got caught up on that.

Back of the board was clear.

Tomorrow I'll hit Radioshack for these:
http://www.radioshack.com/product/index … Id=2062350
http://www.radioshack.com/product/index … Id=2102510

And see if I can get things working again before the new stepper arrives.