Zonestar printer does not detect x axis limit switch

[Charlie1]

Hi, all - my Melzi board on a Zonestar P802Q (prusa I3 class) printer has stopped detecting the X axis limit switch. The switch closes normally, and the resistance drops to zero on switch closure. But the board does not detect this; it simply continues to grind away at the belt until I shut down the printer. The problem 'just started' after I cancelled a print through the software menu (rather than simply cutting the power, as I had normally done previously).

I tried a shut down and power up cycle, with no success. I depressed the reset switch on the board, with no success. And I flashed the latest firmware update onto the board, with no success.

I have found the following bit of information on the reprap website:

================================================== ===
X axis only moves in one direction and/or Endstops do not work

This may be due to bad 644P Fuse Settings. The settings come from the bootloaders "hardware/arduino/boards.txt" file from sanguino. Good setting for 644P board are:

atmega644.bootloader.low_fuses=0xFF
atmega644.bootloader.high_fuses=0xDC
atmega644.bootloader.extended_fuses=0xFD
Then you need the reburn the bootloader with these settings.

================================================== ====

The trouble is, I haven't the faintest idea what this means, or how to apply it to solve my problem.

Can anyone interpret this?

Or offer suggestions as to how to fix the limit switch problem?

I'm shut down until I solve this, and I'm spinning wheels. Help.

Thanks - Charlie1

[zx81]

Fuses are settings on the controller board they do various things such as set clock speeds, bootloader options, brownout detection etc.
You would need a chip programmer to change these settings (assuming it's an avr.. avr tiny, avr dragon, JTAG ice etc) I wouldn't mess with these settings it's not like you can change them without the programmer!

I'd look for a wiring fault .. issue a M119 command to check your endstops open/closed state.. then hold the switch in and issue it again, this will tell you if your controller can see the switch.

You could also plug in one of the y or z switches and try and stop the carrige manually.