Sunday, 15 November 2015

Wiring up

In our last exciting episode, I found that the new Melzi board works on the extruder port, as does the new motor, and there is some problem between the board and the extruder motor when mounted. Let's see what today brings.

First trying if the old extruder motor actually does work. It would be nice to not have to take stuff apart to get it out. Setting the extruder temperature to 185, but noticed that it started out say 43, which is definitely too high. Shouldn't be a problem for now, though, since I have no filament in there.

Yay! The extruder motor works! Now I'll let the print head cool off while I mount the other things.

Wired up the stops and the bed temp. The X, Y, and Z endstops work. How do I know when I don't have motors wired yet? I turned on communication debugging, made each axis home, then pressed the endstop and saw it triggered in the debug window.

The bed thinks it's at 38 C. That both temperature sensors are off by about the same amount maybe hints at a wrong setting.

Next test the bed heater. When I tried starting it, the power supply stopped. Turning it off for a while then on again made the power supply happy, but something is bad. I don't expect that the bed would draw more power than the extruder heater, but it looks like the fuse is blowing, even when I don't have the extruder heater on. Short circuit is most likely then. On close inspection, there's a loose wire:

Rewired more carefully, now it works.

Wired the motors, X, Y, and Z work beautifully. Since all parts of the Melzi work (except the temperature adjustment part), I mounted it back on the frame. Now try to get some more info on the thermistor problem... Aaargh! Nothing works! Yelp! Oh, it's just the yellow power that popped out when mounting it. I have to say, the Mendel90 doesn't leave much room for all the wiring. If I were to redesign something, it would be putting the Melzi out at the rear edge and the resistors in the corner. Might be too far away for some power supply cables, though.

I got tired of how the power connectors are awkwardly pressed in. Instead, I put a nail on the black wire and a larger wire on the yellow, soldered them well and wrapped them in insulating tape:

After this, Y and Z works fine, but the X motor has a ticking sound when doing nothing and is very rumbly when moving. Apparently, that's what happens when the red wire gets pulled out. Reattached, but boy is that a bother. Upgrade idea: Attach jacks on all wires.

Everything works now except the extruder connection and the temperature. Looking at the connections first. With the extruder motor disengaged, I measured the resistance between the connectors. Between K, B, and G, there is connection, but not between any of those and R. Even when the print board at the extruder is disconnected.

Compared to the other stepper motors. They have connection between R and B and between G and K, but not between those groups. According to the schematics, they are all the same. So something is wrong. Again:( According to an electrical engineer who came by at open house, I should understand what the variable resistors do and how to safely adjust them before powering up. That might have been a good idea.

At this point, my laptop ran out of power and I had no charger with me.

Regarding the temperature measurements, one page mentioned that a 50K thermistor would show up as 40 C. That's what would happen if there's a short-circuit that puts the two thermistors in parallel somehow.

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