Swapping out a bad galvo; the PhenixTech PT-20K is a drop in replacement, +video of tuning


Thursday before last my Y-axis galvo failed - progressively. First it started expanding prints by about 2/3% between each print, but was stable during a print. So I was able to use the trimpot method to adjust it, after which it would be stable for maybe one or two prints before it started expanding again. Following about 5 cycles of that, on friday just gone, it started expanding during a print. Similar to what happened to Vince Erb in this thread : https://support.formlabs.com/entries/39240678-Skewed-after-latest-firmware-update

The first below picture shows two of my 80mm test pieces. The top one was printed aligned with the X-axis, and measured about 79mm, the bottom one was aligned with the y-axis, and you can see the sides which are supposed to be vertical have a distinct slope.

When my y-axis galvo first decided to stretch for new horizons, I thought perhaps it would need replacing, and since I’ve publicly voided my warranty on these forums several times over - I ordered a set of the Phenix Technology PT-20Ks as pointed out by Korben Dallas (thanks!!!) in this thread https://support.formlabs.com/entries/38873873-Adjusting-the-galvos-for-better-accuracy-success- They were only $166 from stagelightmall and that included shipping to the UK. You may even be able to find them cheaper elsewhere.

They actually arrived on the same day my galvo really lost it and started expanding during the print, so yesterday I replaced the Y-axis, and tuned it http://www.youtube.com/watch?v=Kx5qwWXJ1X0  I’m now 6 prints in (7th is running) - and everything looks good. Dimensionality is stable.

So lets go through the process of swapping out a bad galvo. There’s not a lot to it. The actual replacement is easier than putting a graphics card in your PC, the only tricky bit is adjusting the galvo so that it’s oriented centrally - see in my video above, where after positioning it approximately, final placement proves a little challenging.

1) Undo 3 screws. Two under the base of the Form1 that attach the galvo daughterboard to the Form1 case through the heat sink at the base of the daughterboard. The third screw you need to loosen in the machined aluminium block that holds the galvos and the laser.

2) Pull out the daughterboard and the galvo and unplug the cables.

3) Move cables over to new galvo and daughterboard. Note, be sure to pair the galvo axis label with the daughterboard label, X with X, Y with Y, it doesn’t really matter if you put an X galvo in the Y slot (Formlabs made this mistake this on Obtainable lamb) so long as it’s paired with the right board, the only difference will be how the galvo ends up positioned in the metal block.

4) Position the galvo in aluminium block - the edge of the integrated PCB with the cable should be oriented at 45 degrees to the edge of the metal block, and the shiny mirror side should be facing the laser if you’re replacing the X-galvo, or facing the X-galvo mirror if you’re replacing the Y-galvo. You don’t have to be exact, you adjust it’s position while running a test pattern so you can see and get feedback on it’s position. Tighten the hex screw enough to hold the galvo in place so that it requires a little force to twist it.

5) Put the daughterboard in place - you may want to coat the bottom of the heatsink with thermal paste, it seemed like a good idea to me - and screw it in. You’re now ready to start tuning for accuracy, see my youtube above.


a: Shows 80mm test parts printed oriented with X-axis above and with Y-axis below when Y-axis failed totally and started expanding during prints on Friday.

b: Formlabs galvo daughterboard next to Phenix Technology PT-20K board. They are very very similar, but not identical - I think this is because despite the Formlabs logo printed on the original, that they are both manufactured by Phenix Technology (or at least licensed by PT to FL) but the PT board is now version 6 whereas the FL board is version 5. You can see the version numbers printed updside down near the top right of both boards. Hopefully this means the version 6 board will be more reliable. It would be interesting to hear from a more recent Formlabs customer - to see whether the galvo daughterboards have been upgraded.

c: My original Y-axis galvo removed and placed on the left of a PT-20k - they are identical in dimensions. Note the X label on the galvo which was put in the Y-axis slot by formlabs - it didn’t matter of course.

d: The PT-20K X and Y set - with plastic covers protecting the galvo mirrors. Minus the other accessories they came with, which I guess I will just have to throw away.

Retro Form 1+ Guide
Y-axis very limited range of motion
Galvomotor model

Awesome write up and video. Thank you!


That is very cool stuff Kevin!


Thanks guys, I have to say - I am much, much happier about the future with my Form1 now.

All we need now is to source a complete replacement laser module. Even though although laser failures don’t seem anywhere near as common as galvo failures, it still happened to my first printer. Ideally I’d like to be able to plug in a whole module rather than having to crack a failed laser diode out of the case and solder in a new one…


Nice. I’m planning on starting a thread sometime soon relative to my discussions with formlabs that might help on the topic of leveling.


Oops wasn’t done with that post. Anyway thanks a lot for all of your efforts to document your modifications your willingness to void your waranty and announce it publicly has made this a better place for us all.



seriously, you’re a genius!

It’s not gonna take long and you’ll be able to build the Form 2 :slight_smile:


Good work, Kevin!

Also, another user on the forums has sourced the peel tray stepper motor so the info’s been added to the Unofficial Wiki. http://form1printer.pbworks.com/w/page/73582883/Replacement%20Components

If I can get a broken laser module in hand, it shouldn’t be too hard to sample/source diodes and come up with a fix.


This is good stuff.  Thanks for sharing your findings!


Does anyone have links to a current source for a Form1+ Y galvo?