Ok my troubleshooting is over on that factory encoder. It fell apart. After taking it off the circuit board, the one I had appears to be this one.
Datasheet,
Digikey catalog (top: figure 4)
It's probably not exact, because the OEM one was 30PPR and this one is 20PPR, but I can't find 30.
I notice that it was laid out, in circuit, more like the sample circuit shown, with the switched common and capacitors (but I cant find the 10k resistors on the board that the encoder was on).
I suppose there are some reasons why you wanted to switch + vs. com.
Well, I'm going to order a few more of these and give it another go.
probes look like.
at uni all the freshman take the probes and shove them into things so the tips either break or they do fun things like measure the resistance of a hot soldering iron and melt it or short their circuit and blow the oscope, oh how fun it is. 
We even have some platinum tipped probes, but those are locked away for special use since they are so expensive and break if you give them a dirty look!
Linear Mode
