Ground PC boards.  

Re: Ground PC boards.

the Frame ground is NOT connected to the output voltage minus connection. I see some capacitors that connect the -12V to Frame ground.

Why would it be? Shorting one of the outputs to mains ground would be a bad thing, since many customers want an isolated power supply. Those who want it to be mains grounded, they can always short it themselves. Moreover, why ground just the negative output? Someone would want to use it as -12V power supply and in that case you could want the positive output to be connected to mains ground (i.e., the negative side of a power supply is not always ground in circuits).

The capacitor is there to suppress high frequency voltage between input and output of the power supply caused by stray capacitance of the transformer. In case of class II (double insulated) power supplies (that have no mains ground connection), the other side of the capacitor is connected usually to a divider between live and neutral (in class II power supplies, you do not even know which one is which, since there are usually two orientations you can plug the cable into the wall socket). This is the reason why you can measure half of the mains voltage if you measure AC voltage between output and mains ground.

Re: Ground PC boards.

Thanks NiHaoMike for your explanation.
If I read trough all the previous posts on this subject is it correct to conclude that:
1) the USB is floating for a reason (isolate lpatop/PC from printer), do not ground it.
2) it is okay to connect the Prusa frame to PSU frame (ground it), as it is floating now.
3) grounding the stepper motors is okay, not sure if this will help (than you should also consider to shield the motor cables).
What is your opinion to increase your proposed "fusable resistor" from V- to PSU frameground to a much higher value (e.g. 100 Kilo Ohm), it will prevent the EINSY board to completely float from Frame ground and therefore might solve the reported electrostatic sensitivity?
I'm afraid I can not be of much help as I have just basic knowledge of electronics (so it is better to leave this to the experts before I will create confusion or make wrong conclusions 😀 ).

The 47 ohm value was chosen because that's what I had and it's also very close to 50 ohm, a common impedance in RF circuits. We'll need someone with a VNA to measure the actual RF impedance of the wiring from V- to chassis ground at the motherboard end with the motherboard disconnected. Then that would give the "ideal" termination value.

It is counterintuitive to beginners that shorting the remote end of a cable is not an effective way to stop RF such as high frequency noise. Read a little about transmission line theory to understand why.

USB shield, USB Signal integrity

Hello Tomp,
Thank you for the tutorial on grounding. It was good information. In my opinion, I am following the rules given in the tutorial precisely.

You asked why am I doing all this? The reason is that I have heard of and read reports about these printers being susceptibility to print failure due to someone touched the machine. I'm trying to find a reason or reasons why this should happen. I certainly do not want my new, super cool, printer plagued by this problem. My career has been in Electronic Engineering. I am quite capable of figuring this problem out without doing stupid stuff and causing a catastrophe.

That's why I made an effort to measure and published what I did, in my humble opinion, referencing the PC boards to Earth ground is a positive step in trying to resolve the "glitch" problem. As proof of modifications made, the system works fine, I'm not drawing excessive DC current and nothing "blew up."

Now if someone walks across a carpet and develops an electrostatic charge and touches the machine, the ESD dissipates directly to the frame/Earth ground rather than glitching the "floating" PC boards, wiring, and components.

I finally got a schematic of the Atmega 32u2 USB Serial converter circuitry. The USB receiver and transmitter are floating on GND1 and powered by the host computer. For a laptop system, this may be fine. However, for a mains powered system, this practice could be questionable. The USB shield does not connect to GND1. Instead connects via a 4.7uF and a 1Meg resistor in parallel to GND1. Also, there is a back-to-back 30V Zener diode from the USB shield to FGND which shows to be equivalent to Earth ground. Since the PC board does not connect to Earth ground, this connection floats along with the PCB floating ground plane.
In my present, chassis grounded PC board configuration, the ESD protection diode direct glitches to chassis/Earth ground instead of glitching the entire PC board ground plane along with associated circuitry and wiring. It is not clear where the glitch would go without a direct path to Earth ground.

The USB cable:
This component is more than just a simple twisted wire pair. There are six components involved that comprise the USB cable along with their associated dielectric insulators. Namely: Shield, Drain, Vbus, Ground, D+, D- (Twisted Pair). All these wires and insulator dielectrics play part and parcel to the Impedance of the USB twisted pair. The USB's standard is 45 Ohms common mode and 90 Ohms differential. I believe it is closer to 35 Ohms common mode and 85 Ohms differential for USB transmission lines' impedances. I could get into more details about the Physics of the USB transmission line, but that is way beyond the scope of this correspondence.

USB Signal integrity:
If the transmission line does not terminate in its' characteristic impedance, reflections will occur. Reflections on the USB transmission line will corrupt data. The schematic shows 22 Ohm resistors in series with each data line. What is the impedance or equivalent circuit of pins 29 and 30 in the Atmega32u2? This impedance should agree with the USB's standard stated above.

Re: Ground PC boards.

why not just enjoy your printer and print you way over thought this and now its boring 😆 😆 😆 😆 😆

Re: Ground PC boards.

Ok followup on this topic:

I messaged Ultimachine multiple times about this, how to ground the board, but never got a reply from them.

Next i asked our PCB designers in our company on what they think about the Einsy's schematics, and they said never to ground the Einsy in any way.
It's designed to float. Connecting the Minus pol of the Einsy can blow something if you connect a PC to the printer.

Lastly, i found Lulzbot's new Printer, the Lulzbot mini 2, which also uses the Einsy (Retro not Rambo, with Endstop switches and 12V fans)

https://ohai.lulzbot.com/project/final-electrical-assembly-hibiscus/hibiscus-beta/

Look at step 3: they screw the Einsy to the frame with the 4 corner screw holes (that are connected to minus)

Look at step 4: They are using shielded motors cables and shielded motors.

Look at step 9: they are connecting all motor shielding cables to the frame:

Look at step 12: they are connecting the Grounded frame to another case part here:

Step 4 of this page: https://ohai.lulzbot.com/project/electronics-case-hibiscus/hibiscus-beta/
which gets connected directly to earth ground.

Oh man, what a little clusterf*ck this is.

So lets recap:
Prusa lets the Board float
Lulzbot connects the Board directly to earth ground
PCB designers say it's designed to float.
USB Spec says Slave devices are designed to float.

So take away what you want from here.

I have shielded my motors and motor cables along my Aluminum frame to ground, but i'm letting the board float.
Personally i think that's the right way to go here.