Strange temperature readings

[RobVH]

Hi, I have a strange problem with the rambo 1.2a board I purchased recently. The heat bed and associated thermistor works fine, it reads the temp and heats up as expected. The hot end thermistor reads fine too, but when I try to heat up the hot end both the hot end and heat bed temperatures instantly increase to 80 degrees from room temperature and the hot end doesn't heat (the mosfet led doesn't turn on). When I then turn off the hot end the temperatures drop instantly to 60 degrees and stay there. If I disconnect the heater cartridge and again turn the hot end on the mosfet LED does turn on.

If there a fault with the board? I notice that the 1.2a batch was very quickly replaced with 1.2g.

Rob.

[Star]

Hi,RobVH!

Sincerely sorry for the delay.I think there may be a connection problem or something wrong with setting up proper configuration of Marlin.I suggest you to browse this website http://www.geeetech.com/wiki/index.php/Rambo .There is a diagram of pin for Rambo and the imformation in it will tell you how to set the parameters of configuration.h.Hope it is helpful to you!

Best wishes to you!
-Star

[RobVH]

Hi Star, the problem was a blown F3 fuse, which in itself is odd since it had never been used. The strange behavior was because the Geeetech Rambo has the logic powered through F2 (along with the motors) where the normal Rambo has logic powered through F3. Normally if F3 blows the board doesn't function and the problem is obvious but with the logic shifted to F2 the board stays powered and other functions (bed and motors) work. It seems that when it tries to power the mosfet with the fuse blown some odd things happen.