First time trying with my new laptop, so of course half an hour went by finding out that the wifi password isn't on the wiki anymore. But now I'm connected.
First order of business: Get the firmware back up and running. I tried with the old version from the Mac, but without luck. Instead I grabbed a Mendel90-specific Marlin and uploaded that, after moving an old clashing dir out of the way it worked.
Cloned Printrun and ran it, all axes work nicely. Temperature sensors still read 40C. I measured them before putting power on, and they were at 11.5K ohm. Now they read - (!) 90K. There's probably a reason they change when there's power, I'm not going to worry right now.
This post claims it's because some Melzi boards still have 10K instead of 4.7K pullup resistors for the thermistors. And indeed, it does. So even though 3dnielsen.dk calls this a 2.0 Melzi board, it has old resistors. Bother. The old one does have 4.7Ks.
Manually holding another 10K resistor changes the temperature reading a little bit, but not down to 20C. I might just not be able to hold them appropriately.
Three options now:
1: Buy a new board. Expensive, and I'll have to rewire, and it may have other flaws.
2: Resolder the SMD resistors, taking the ones from the old board which are correct. Haven't tried soldering SMD before, but these are relatively large:
3: Recalculate thermistor tables. There are some posts about this, but they all assume you have a way to measure the temperature. I tried measuring my hotend earlier with an infrared meter, but it never read anywhere close to what it should.
Just for shits and giggles, I wired up the old board with just power (easy now with the name), ETemp, EHeat, and direct connection to the extruder motor. Heat it up, and whaddyaknow, it extrudes! Well, runs the extruder motor at least. So it worked all along, maybe just with too little power and definitely with the wiring problem. So now I have another option:
4: Switch back to the old board again. Try not to cry.
At least I didn't start soldering before I tested this. Could easily have destroyed both boards for nothing.
I think I'll spend the next evening soldering the tips of all the wires going into the Melzi, so I don't have further issues with wires going off on adventures.
If need be, I can have separate wires circumventing whatever it is that's broken with the normal extruder motor wires.
In other news: FabLab now has no less than three (3) laser cutters, including one 150W oxygen-laser 1,5 m2 cutter. It slices metal sheets. Sweet.