Formlabs Form 3L

Formlabs Form 3L - root causing its issues (literally)

This printer might be the most unreliable printer I've ever touched. Formlabs support makes the nightmare bearable.

Ok, jokes aside, this printer proved to be much more of a project than a tool. Over my summer internship I used a Form 4 religiously and was impressed with the quality and speed, so much so that I wanted to buy a Formlabs printer for my own work. Little did I know this would prove to be a mistake. I ran into all sorts of issues, from code 67 to code 234, but let me take you through the process I went down to figure this thing out.

I first saw a listing on Facebook Marketplace. I drove with my friend Adam to Vacaville and loaded a car to the brim with Formlabs equipment. Picture below of how much filling happened. The second one was picked up in San Jose.

And it worked. Prints were reliable for the first 2 prints, which worked great. Then came continuous errors. Formlabs support said the machine is broken and beyond repair. To their credit, these machines are second hand and I'm not sure how they ended up with their respective owners. Support was fast to respond and always works on doing right by the customer. Using dmesg, we were able to see the faults for ourselves.

And so the printer was taken apart to unveil a bunch of redundancy. The biggest was a microcontroller on the "momo" board one printer had an IMX based solution another had a SMT32G4. This momo board houses a the below is the Sitara module. It's made by Compulab, but I think Formlabs bought the design? I'm not sure how that works, and I'm impressed that Compulab allowed Formlabs to do this. The Sitara has a ton of spare micros inside of it so im not sure why this was broken into 2 parts. 2x dual-core Programmable Real-Time Unit and Industrial Communication SubSystem (PRU-ICSS) and 2x dual Arm® Cortex® -M4 co-processors (IPU1 and IPU2) to be exact

Below is the QSPI for the Sitara. UART boot log off of the momo (the mainboard, it's just what Formlabs calls it). The most amount of security on this device was the crappy programmer I bought, the CH341a, preventing device readout. This thing was so flaky, but I just bought a nice FPGA-based programmer coming soon. Yay!

Adam spliced and diced some SDK U-Boot to generate cooked.bin, and boom, we are in. Once in, we dumped the entire file system to a USB drive for further analysis. That was a cooked USB cable lol.

Once we were in dmesg, we were able to see the printer for what it is, chock full of URB errors. I didn't know much about USB, but this was a masterclass in unreliable USB connections. URB (USB Request Block) is any relevant information needed to execute a USB transaction and deliver data and status back. It's kernel level and structured to facilitate communication throughout Linux and to the different control nodes of the printer. URB error code -71 was being fired on prints that were failing.

Interestingly, both of the printers had these errors when combing through the logs. Formlabs seems to have attempted to fix the problem by retrying transmission a few times before ultimately resulting in error 67. This leads us to believe that this problem plagues all Form 3Ls, albeit to differing extents.

I opened up the printer, and with Adam, started to work on understanding the issue.

The printer has a -24V and +24V bus sent to the LPU (Light Processing Unit). These devices use a solid state laser and galvo system to scan the base of the resin vat in order to cure the resin. From my understanding, this was done to circumvent a patent (I totally could be wrong), but from my perspective this is far inferior in every single way to MSLA, due to a massive increase in overall machine complexity and worse performance (slower), albeit with lower force on the FEP film.

These +/-24V supplies have terrible ripple. Vpp was close to 500mV at idle, and under load the story was the same. Bottom line, there was a ton of noise. This noise was being injected into the LPUs and the xhub board.

The xhub board is shown below. It's a PCB interposer used as a USB hub as well as a power supply breakout for the 2x LPUs inside of the Form 3L. This board was at the heart of our problems.

The USB hub on the xhub is a Cypress job. Below are the operating characteristics of the device. We noticed that the Vmin and Vmax of the 3.3V rail supply generated by the on-xhub buck converter was +/-300mV. This could cause the URB issues that the dmesg log was firing, as the device was subjected to out of normal operating range conditions.

To confirm this, we shorted out the crystal during operation (forcing the hub's clock to 0) and were able to recreate the URB issue. At this point, we were beginning to understand the issues.

It was clear that the problem was hardware related, so Adam traced the PCB to obtain a netlist.

Once Adam made the nets I set to Alitum to develop a custom board. This time pulling out all the stops.

Due to signal integrity being questionable. a TUSB221 was added in conjunction with a high USB hub with tunable DC bias from SMSC (microchip). This hub, the USB2512I proved to be a good tool for the job. The configuration to load from was generated with a EEPROM packer code tool that microchip provided.

The boards were fabbed and programmed. Turns out there was too much capacitance, so I depopped the tants.

Also had an issue with the -24V power supply generating 1V. It was due to a broken resistor, but I believe we caused that, not Formlabs, so skill issue.

The printer has not fired another URB issue, and prints have been successful thus far. A resin tank leaked, which sucks, but that's a solvable problem. Thank you, Formlabs support, for squaring me away with a new tank!

This was a difficult project, but I learned a ton about USB and continued to sharpen my debugging skills. Shout out to Adam for being as crazy obsessed as me and wanting to get to the bottom of these issues. Also shout out to Formlabs support for the initial troubleshooting guidance. Hope this writeup can help the Form 3L series of printers and provide value to someone in this world.