Maybe my mistake has been not to refer more directly to the actual code. Over the last 24 hours I have been steadily working through the last two years of email conversations. Loftur keeps the group informed of each new version of the firmware and the newly added features. Sometimes he jumps the gun, but then releases a newer version shortly afterwards.
Well, well well! I think I have discovered why the final part of the loop controller is not working and perhaps why the A4975 stepper motor driver ICs are running so hot. I have just been doing some continuity testing working back from the stepper motor connector, K1 and noticed that there is continuity between C11 and C12 and also between C15 and C16, and there is no continuity between the legs of say C16 and C14 connected T2 etc, all of which implies that I have oriented the common mode chokes, T1 and T2 exactly 90 degrees out from where they should be – I think and I hope… They are both surface mount with four points of contact(!!!!), so there might be some interesting re-working to be done. I actually have one spare if I bugger one up. Also I may need to replace the eight 10nF ceramic bypass caps nearby. But this is progress of a kind.
I wonder what made me install them this way. Surely not simply the orientation of the writing on the package!?!?!?, or the oblong shaped pads on the PCB?!?!?!?! Two visual cues to be misled by!
I suppose I should be optimistic about the transformers being okay if they still show continuity… There’s a big lesson here about using the schematic during the construction and not simply populating the board. And maybe even being curious enough to actually turn the component over to see its magic revealed and be inspired to orient it correctly.
And now of course when I look back to page 8 of the BOM and building instructions I can clearly see the correct orientation of the transformers. Oh me oh my!
And I have just noticed during my rapid review of the emails on the Loop Controller list that on 8 May last year, while advising someone about testing the sense of the stepper winding connections, Loftur dropped this comment, “Also, have a careful look at the circuitry around the A4975 stepper controllers. One fairly common mistake is to mount a common mode choke incorrectly.” I’ll say!
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