K8400-part problems and issues

printer story: starting with the bad pulleys, got replacements end February–works now fine, first Print was ok–install the second extruder–start printing-- While the Printer was working, the printer got trouble-- some smoke was comming out from the mainboard, near the X-axis Motor driver modul.
Some red LED are on, I removed all driver Modules and all connection going to motors etc, means minimal configuration.
The display light was only on, nothing to see, also the Powerregulator 15V to 5 Volt ( L7805) on the mainboard was heating up, the output voltage drops down from 5 Volt to 2.5 Volt in a short time, looking like something shorted behind.
Yesterday I got the mainboard ( warranty) back.
Installing only with Power und LCD Flatcable— Result no Text on the screen, connect all cables, repower —about the same-- I saw with low contrast ( doesn’t matter the contrast adjust, only nothing or very low contrast) the boot screen with VERTEX on the screen and PRINTER READY ( but on a different Position-- not like normal),
Blind I can use the Switch to initialise the printer-- runs in the normal homepositiom, but on the display I got some strange letters like %&?&%%$!§"§§-- some with normal contrast-- but nothing correct written.
With USB connection I got only the backlight and no USB connection with USB port- the PC see nothing on USB.
Today I will remove the LCD and will check the Flatcable connections and soldering, but all was working until the mainboard died.
Annother think I can check?
My last check was to runn the mainboard without driver boards, only power and display and reset button–Reset is working on mainboard and LCD, but still not full LCD function.
Any Tipps?
I am not happy about this Printer history


Which Arduino IDE version did you use?

You need to use V1.0.6 and not V1.6.0!


V1.06 nothing changed since the printer was running


Try to redownload and reupload the firmware?


did it, USB port works for Arduino 1.06-- Firmware is reloaded, but still the same LCD Problem stange letters and around no contrast

Try removing the stepper drivers and try again…


did it , try to run in minmal configuration–nothing change

I think then that your motherboard or your LCD is just faulty…


I removed the LCD, check connector and soldering–looks fine
But also checked the voltage-- LCD get instead of 5.0V only 4.05V, also on the mainboard the U2 output have 4.98V, after the Diode D5 also 4.05V-- something wrong with the new mainboard-- with a diconnected LCD the 5V is still 4.05V–!
And now?

That will be the problem… You need perfectly 5V otherwise you will run into problems.
Check if the power supply delivers 15V to the mainboard.


Powersupply 15.1V, U2 Input 15.1V, U2 output 4.98V-- after Diode D5 4.05V looking like small overcurrent on mainboard–could be all…–all driver modules, Motors etc disconnected–still the same



Voltage from 5V regulator seems to be correct (4.98V), regulator is not heating excessively?
If not, I’d replace diode D5.

Ok , I will replace D5 with a Diode 1N4007, but for D1 in Front of U2 on site do have 15.1V ( powersupply ), the other site around 14.3-- make sense for a Diode— going to the 7805 regulator ( U2) Input 14,3V output 4.98V-- so far ok, but why I do have to have 5V after the next Diode (D5)-- The regulator U2 ( 7805) is normal warm not heating.



Nothing really better, I used a new Diode parallel to D5, the Voltage was now 4.3V — the Dsiplay function was also bad— something strange with the new mainboard related to 5V.
Any ideas?
DOA mainboard?


Usually there is a voltage drop of 0.6-0.7V over a diode. Can’t understand what this diode after voltage regulator have for function. Unnecessary according to me. The diode before voltage regulator takes care of polarity issues and voltage reulator have internal protections as well. I would shortcut that diode after voltage regulator then you would have same voltage to the board that regulator provides.

I do have the same understanding about the Diode Function, would be nice someone can measure the voltage D5 to ground on a running system.
to shortcut the diode may cancel the warranty

This diode is necessary to avoid current returning to the regulator when the power supply is turned of and the unit is still connected to the PC via USB.
Shorting it is not a good idea.
It is normal that the voltage after the diode is 5V minus a diode drop, this is not a problem for the correct operation of the board.
A drop of 1V, as you mentioned before does not seem normal.
We’d suggest to return the board for inspection/repair. Make sure to include a detailed fault description.

I will send it back incl. the display board—but it does mean the 4 weeks the printer ist still down.


nothing back until now— slow prozess and no feedback


We’d like to check with repair dept what the status is, but we need a name and/or address.