RostockMAX no longer responding (after a few commands)

[Quocket]

Dear community and forum wizards

I added a second hot end to my MAX v1 and noticed an issue where I wasn't able to find a solution for so far (the printer worked fine for the last almost two years with a single E3D v5 hot end before).
Everything runs nicely (heating the bed, heating EXT0 & EXT1, temperature feedback and so forth) but after a while, the printer stops responding to any command (extrude, change temps, G28…). The Queue in Repetier Host (0.95F) just increases the number of “waiting commands”.
As soon as the printer reaches the mentioned state, the system does also not respond to any change done using the LCD panel.
Here is a typical start sequence which leads to the unresponsiveness:
• Switch on the Printer
• Connect to the printer in Repetier Host
• G28 ; Home
• M140 S79 ; set Heat bed temperature
• T0 ;Select first extruder
• M104 S236 ; Set temperature of first extruder
• T1 ; Select second extruder
• M104 S246 ; Set temperature of second extruder
• M46 P6 S255 ; Set PEEK fan to full
After reaching the temperatures on all three probes, sometimes the extruder still works (e.g. I can extrude 100mm of filament on extruder 0 or 1) sometimes the control is already gone…
I suspect it has something to do with "changing the focus" from one extruder to another. I was able to print the calibration cube (the one with the center holes through each side) but I manually cancelled the print after the few first layers that “need” support structure because of a nozzle offset inaccuracy (this was at a height of about 8.5mm / ~Layer 57) - so I'm struggling to understand what happened to the printer since then

What I've tried so far:
• Changed communication speeds (basically it just runs with 115200)
• Replaced USB Cabling and USB Port
• Changed Host Software (tried pronterface (February 14 version) and RC2 of Repetier Host 1.0)
• Replaced PSU as I experienced random “black-outs” with the stock PSU --> the blackout problem was resolved with the stronger PSU
• Replaced my own configured 0.91 firmware (I got this when the seemecnc official version was not released) with the today's version from seemecnc
• Cleared the EEPROM before uploading the new firmware
Any Idea what to try next?

[1ggy]

Hmm, I have a similar problem with mine, but I've had the problem since I got the printer. Mine doesn't show waiting commands, but it won't respond to anything either.

[Quocket]

Dear Community
After struggling with this issue for some time, I accidentally stumbled over the solution. It seems that there was something wrong with my version of the firmware. I didn't take the time to analyze line by line but after generating a new version 0.91 rev 8 firmware, the issue was gone and didn't came back so far (couple of weeks and about 24h of printing time).

so - case closed - and if anybody encounter a similar issue, try creating a fresh firmware from the web site.

cheers
Tom