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A quite strange problem on Rambo SPI interface  

New Member
A quite strange problem on Rambo SPI interface

Hi all.

TL;DR: Apparently my SPI interface correctly communicates with Trinamics drivers but not with the external flash nor SD card, even if all these devices share the same bus.

A few days ago I switched on my MK3S+MMU2 as usual, but instead of the normal boot sequence, I was greeted with an error message "External SPI flash W25X20CL not responding". I resetted and switched off/on a couple of time without success. I even disconnected the MMU2 to see if things changed, and re-flashed the last firmware. Same error.

I also noticed that in the main menu there was a line saying "NO SD CARD", but an SD was in the slot. I tried all of my SD cards, noone of them worked (printer detect the SD insertion, but can't read data from it). SD worked when checked on a PC. 

I connected to the printer via USB port, and (besides the same errors shown in the log) it prints without problems when driven from a computer. 

I thought the SPI port of the microcontroller had somewhat failed (SD card uses the same SPI port as the external flash) but, and this is my doubt, the SPI bus is also used to talk with Trinamics step motor drivers. How can the printer works without errors if it can't talk to motor drivers? I looked at the schematics, there are no "fuses" or other protections between devices on the SPI bus: if it can talk to Trinamics driver, it must talk to external flash and to SD card. I didn't check the firmware, but I suppose that there is an error check in case of communication failure with Trinamics drivers. 

So, now I'm puzzled. 

I had a long chat with Prusa customer support, they had me do a factory reset and recalibration of the printer, but with no effect. They said that they could send me a Rambo replacement board, but I bought the printer from a reseller here in Italy, so they said me that I have to settle the matter with him. 
But I need the printer to complete a pair of projects, so I bougth a new Rambo board from Prusa and for the moment I'm printing via USB.

Any idea about how there could be a "selective" error on the shared SPI bus? 

Posted : 07/09/2019 3:29 pm
New Member
RE: A quite strange problem on Rambo SPI interface

I don't really have any useful information to add here - other than to say that my printer (MK3S + MMU2S) is showing the exact same symptoms.
SPI error message at startup + can't read SD card (though card detection works).
Printing from a Pi Zero W in the Einsy port works fine, with colour switching etc, so it is just the external SPI + SD card issue.

For me it seemed to happen after flashing the firmware (even though it was the same version - 3.7.2) while installing the MMU, but it may just be coincidence that this is when I happened to reset the board as the printer is usually left turned on.

Posted : 08/09/2019 11:52 pm