Issues-
One of the scales died, had to jump through a bunch of hoops to convince the seller what was happening & wait 3 weeks for a replacement.
The replacement scale appeared to have some issues of it's own, plugged into the Y port it worked fine for 3" or so of travel then it started driving the X axis nuts- rapid changes in the reading, like 5 or 6 times normal rate. Sometimes the x would just start counting up at an extreme rate, sometimes moving the x would affect the Y. Tapping a scale would start or stop the craziness. The Z axis worked fine, rock solid.
I suspecteded it was generating some noise on the 5v power rail, after sporadic troubleshooting trying to pin down the source of the problem I eventually ended end up getting a replacement Y scale from a different supplier.
Same thing
Then the X stopped working at all
Had to be the DRO.
So I contacted the seller again explaining the the situation & what I had done to isolate the issue & why I thought the DRO was bad, I also mentioned the two year warranty the advertised on their ebay listings as well as on the back of the manual. After some very creative miss-interpretations of the correspondence they just stopped responding altogether.
Grrrr.
With nothing left to lose I opened up the DRO & started tracing things out-
View attachment 352808
The inputs hit the main board & go through a R-L-C-R-C-R-C-R-C conditioning circuit. There's 3 signal lines per port although the supplied scales only use the A & B lines, I'm guessing the 3rd is for the half rate Z signal even though the manual doesn't show it.
The signal lines run to hex Schmitt triggers- X & Y run to U2, Z to U4. U4 would also handle port "U" for the four channel version.
There's also a U7 that seems to be there for an unused usb port & something (W) that might be a serial interface.
Working through with a scope I could see nice clean square signals all three inputs on X , Y (U3) & Z (U4) but the outputs of U3 were low & had a funny sawtooth component on the low side of the signal waveform which was also showing up on all six lines even with only one scale connected. Z out lines on U4 were clean. I found I could see the sawtooth on U3's pin 7 (ground connection) but not on the ground pad it was soldered to.
???
I hit the pin 7 joint for a sec with the soldering iron
& No More Problems 
Everything is now working perfectly.
Lesson learned- you buy cheap from china & it's a crap shoot on what happens after that
So with all that I've now found:
Scales from different providers are wired differently- there seems to be no standardization on pin outs for the DB-9 connector. If you mix & match be prepared to do a little re-arraigning with the soldering iron at the connector.
The Z axis scale could have been a little shorter but I ordered everything the next stock size up from what I figured I needed just to give me some options & slop for alignment.
I've found my x lead screw is no wheres near as good as I thought is was, some spots towards the right end are off by 20 thou/"
The Y axis seems to not too bad but there's still some wear.
Z axis is perfect, guess that didn't get used much.
And that's it.
For now ...
