X Lockup & Scream

OK, I have put a pool and a quarter throught my printer and just finally got my print quality looking pretty nice at 0.20. Axis skipping has only happend like five times over the last six months, only once per incidet, and only one axis per incident. Last weekend my X and Y started skipping several times in a row on almost every print (whistles). So, I recalibrated the pots on my pololus. Set them about an eight of a turn past where they stopped skipping. Got alot less, but was still having skipping. I turned them up a little more. Got a two good prints and they started in again but not as bad as last weekend.

I turned the pots back down a bit thinking the problem may have just been pololus getting hot fom the start. I readjusted the 50mm fan I had blowing on top of my RAMPS and hooked it up to 12v to make it run faster. Still issue mainly with X. I swapped X and Y pololus. Afer one good print, X persisted. I enclosed my ramps in a cardboard enclosure with an 80mm fan blowing in one end and out the other. Got three two prints of a two different things and then on the fourth one my X locks up and start emitting a high pitched hum (scream) with a little grind thrown in.

Do I need a new motor, pololu, PSU, printer...?

Model: Prusa i2 (mixshopdotcom kit)
Supply: PC PSU (mixshopdotcom kit)
Brains: RAMPS 1.4 (mixshopdotcom kit)
Motors: NEMA 17 (mixshopdotcom kit)
Belts: GT2 (makerfarmdotcom)
Extruder: Greg's Hinged Accessable (ABS)
Nozzel: 0.4 J-Head Mk V-BV (hotendsdotcom)
Filament: PLA (seemecncdotcom)
Surfface: Painter's Tape
E Temp: 185
Layer Height: 0.20
Slicer: Slic3r
Host: Octoprint

X and y both move without too much resistance when printer is off. X might require slightly more force than Y. Y moves freely with belt off.

After the box and fan the pololus are staing cool. I can hold my finger on them and not feel much heat. Before they were getting pretty toasty. I cold only touch them for a few seconds. Why did they work this way so long. I appears they didn't shut down unless that's what the bunch of missed steps was about.

monttyle on #reprap suggested I the windings with my meter. Two ohms between coil legs. No shorts between coils.

monttyle also suggested that I make sure the X motor turns freely without the belt and it does. Printer will even still print after a reboot, but X stops and screams again after a bit.

SystemsGuy on #reprap suggested I check my rods for scratches to make sure I didn't have a bad bearing. Rods don't seem to have any.

One more tidbit, there was an incident arround the same time as last weekends day of double contstant axis sikpping where my power supply fan quit about three times in a four seconds and you could see there was a voltage drop becuase it affected the performance of the printer. I unwired the whole printer and checked for loose connections and shorts. None found. Only happend this once.

SystemsGuy asked me to check my v-ref voltage. Said it should be 0.4 volts. After finding the locating the tuning motor current seciton of the pololu reprap wiki page I tuned all my motors to 0.4. Some were high and some were low. It seems this is suppose to be check between the metal of the trim pot and the bottom right pin and your motors need to be on and holding their selvs still. I you can verify this by trying to move them. If they won't budge with just a little force then they are on. If the do move, try using the manual axis controls in your host software (octoprint, printrun, ...) to move them just a little and they should be on and still after that.

Well looks like system guy may have hit it on the nose. v-ref set to 0.4v and I printed a Prusa i2 Z motor holder standing up without any skip. Heres hoping my luck continues.