Hi, I know this problem is quite old, but I finally found out how to solve this, and did not know where else to share it. The piezo signal is very sensitive to electromagnetic interferences. The solution is to shorten this wire as much as possible and as far as possible from the power wires (heater, stepper motors...). A shielded wire may help maybe. So as a conclusion, place the PCB amplifier as close as possible to the piezos and protect the link between the piezos and the amplifier from electromagnetic fields as much as possible.

Hi, I know this problem is quite old, but I finally found out how to solve this, and did not know where else to share it. The piezo signal is very sensitive to electromagnetic interferences. The solution is to shorten this wire as much as possible and as far as possible from the power wires (heater, stepper motors...). A shielded wire may help maybe. So as a conclusion, place the PCB amplifier as close as possible to the piezos and protect the link between the piezos and the amplifier from electromagnetic fields as much as possible.

@Phaedrux OK thank you

What I don't understand is that with the SD card unplugged, I get (with M122) this :
Free file entries: 10
SD card 0 not detected, interface speed: 12.0MBytes/sec
SD card longest read time 0.0ms, write time 0.0ms, max retries 0

And with the SD card plugged :
Free file entries: 10
SD card 0 detected, interface speed: 12.0MBytes/sec
SD card longest read time 0.0ms, write time 0.0ms, max retries 0

So the Duet "feels" the SD card, but that's it. And the 12MBytes/sec value should reveal a SD card issue, but if it is the same with and without SD card mounted, what is the point ?? Nevertheless regarding the SD card, i tried to run a speed test on the SD card (M122 P104 S2) I get :
Error: Failed to create folder 0:/gcodes in path 0:/gcodes/test.tst
Error: M122: Failed to create file

And a complete (again) SD card erase (complete, not fast erase) changed nothing. Could any Duet Team help me to confirm with E3D that it is a hardware issue (warranty relevant) ?

@Phaedrux OK so according to your link, I have a 12MB/s speed so there might be an issue with my card. I will replay the command with my other SD card to compare. What I don't understand is the write time of zero. Do you have any idea of what it can mean ?

@Phaedrux Hi, I bought the card to E3D on August 25th (this year). There does not seems to be any issue with the solderings as you can see... But I have tried with two different SD cards which are working well on my PC so I do not see what it can be else.

@bearer Hi, the M552 S1 command return the same issue :
"WiFi module started Error: Failed to initialise WiFi module, code -2"
And the M122 returns the following output :
=== Diagnostics ===
RepRapFirmware for Duet 2 WiFi/Ethernet version 3.1.1 running on Duet WiFi 1.02 or later
Board ID: 08DLM-996RU-N85S4-7J9FA-3SN6L-1V9RR
Used output buffers: 1 of 24 (1 max)
=== RTOS ===
Static ram: 27980
Dynamic ram: 92268 of which 20 recycled
Exception stack ram used: 256
Never used ram: 10548
Tasks: NETWORK(ready,1884) HEAT(blocked,1476) MAIN(running,2712) IDLE(ready,80)
Owned mutexes:
=== Platform ===
Last reset 00:01:37 ago, cause: power up
Last software reset at 2020-10-08 23:50, reason: User, spinning module GCodes, available RAM 9880 bytes (slot 0)
Software reset code 0x0003 HFSR 0x00000000 CFSR 0x00000000 ICSR 0x0441f000 BFAR 0xe000ed38 SP 0xffffffff Task MAIN
SError status: 0
MCU temperature: min 51.9, current 67.8, max 67.9
Supply voltage: min 0.7, current 1.7, max 1.7, under voltage events: 0, over voltage events: 0, power good: no
Driver 0: ok, SG min/max not available
Driver 1: ok, SG min/max not available
Driver 2: ok, SG min/max not available
Driver 3: ok, SG min/max not available
Driver 4: ok, SG min/max not available
Date/time: 1970-01-01 00:00:00
Cache data hit count 161777938
Slowest loop: 0.15ms; fastest: 0.09ms
I2C nak errors 0, send timeouts 0, receive timeouts 0, finishTimeouts 0, resets 0

   **=== Storage ===

Free file entries: 10
SD card 0 detected, interface speed: 12.0MBytes/sec
SD card longest read time 0.0ms, write time 0.0ms, max retries 0**

                                                          === Move ===

Hiccups: 0(0), FreeDm: 169, MinFreeDm: 169, MaxWait: 0ms
Bed compensation in use: none, comp offset 0.000
=== MainDDARing ===
Scheduled moves: 0, completed moves: 0, StepErrors: 0, LaErrors: 0, Underruns: 0, 0 CDDA state: -1
=== AuxDDARing ===
Scheduled moves: 0, completed moves: 0, StepErrors: 0, LaErrors: 0, Underruns: 0, 0 CDDA state: -1
=== Heat ===
Bed heaters = -1 -1 -1 -1, chamberHeaters = -1 -1 -1 -1
=== GCodes ===
Segments left: 0
Movement lock held by null
HTTP is idle in state(s) 0
Telnet is idle in state(s) 0
File is idle in state(s) 0
USB is ready with "M122" in state(s) 0
Aux is idle in state(s) 0
Trigger is idle in state(s) 0
Queue is idle in state(s) 0
Daemon is idle in state(s) 0
Autopause is idle in state(s) 0
Code queue is empty.
=== Network ===
Slowest loop: 0.14ms; fastest: 0.00ms
Responder states: HTTP(0) HTTP(0) HTTP(0) HTTP(0) FTP(0) Telnet(0), 0 sessions
HTTP sessions: 0 of 8
- WiFi -
Network state is disabled
WiFi module is disabled
Failed messages: pending 2779096485, notready 2779096485, noresp 2779096485
Socket states: 0 0 0 0 0 0 0 0

Hi,

I think my Duet2 Wifi SD card reader is dead. I was configuring
it via the network interface while it suddenly disconnected. The
blue led of the wifi module stopped and rebooting the SD card did
not fixed it. Then I connected the board via USB (Vin
disconnected) to replay the initialization process via the
terminal. And the first error message that I get is
"RepRapFirmware for Duet 2 WiFi/Ethernet Version 3.1.1 dated
2020-05-19b2
Cannot initialise SD card 0: Card is unusable"

I nevertheless tried to start the WiFi again (M552 S0), but I get the
message "Error: Failed to initialise WiFi module, code -2"

So I tried to reload the wifi firmware and the firmware of the
board but it never found the firmware on the SD card, while I can
see it in the /sys folder when I connect the SD card directly to
my computer. I erased the SD card and reinstalled fresh data on
it, but no change occured, still the " Cannot initialise SD card
0: Card is unusable" message. And I tried with another SD card,
but no change. Another example : "Error: M21: Cannot initialise
SD card 0: Card is unusable"

It seems that I am not the first one to experiment this issue
(https://forum.duet3d.com/topic/2646/cannot-initialise-sd-card-0-card-is-unusable/4).

Regarding the card itself, I simply connected it to my motors,
endtops and heatbed + sensor to begin the firmware configuration.
No manual movement of the printing head, no ESD or other bad
treatment...

Am I missing something out or is it a warranty relevant issue ? I bought my Duet2 WiFi last month and was configuring it. Never printed with it yet. But until the WiFi module disconnected and shut down, I had no issue to access it and configure it following the dozuki guide.

Thanks ahead for any help