New Assembly from MK2S Kit -- Garbled Display
Hey Guys,
I took delivery of my MK2S on Monday afternoon and finished assembly last night.
When I powered up the first time, I had no display--sure enough, I checked the cables and I had them backwards at the RAMBo.
I switched them around and got display, but I got only garbled characters on the display.
The only other thing I can add....
When I move the Y-axis back and forth, even slowly, the display will flash.
I'm familiar with power supplies and motor controllers... Of course stepper motors are capable of back-feeding fairly high voltages, but I assume that the stepper supplies are isolated? Hey, what do I know.
RAMBo is about as new as it can be. It's in the enclosure but gave it a look before I threw it in. No visible defects.
EDIT: I also sent this same video to the support email last night, but I'm only creating this thread now so the support email has not seen this thread. Only new information since last night is the voltage spikes shown at the LCD.
EDIT2: Additional photos attached. Stripes were added to the cables by me for your viewing pleasure and clearer interpretation.
Thanks Guys,
Taylor
Best Answer by JeffJordan:
that's really an odd behaviour and I'm running low on ideas here.
the problem might be located at the lcd module, the rambo or the cable.
I know that cables beyond 90cm length will cause problems... but usually these problems are related while reading an SD card.
if you have the chance to get your hands at one or two shorter 10pin ribbon cables with attached connectors, it would be of interest how the display behaves when you use the shorter cables instead.
ah, still one idea left:
can you check the connections between the atmega2560-cpu and the 10 pin connector at the rambo ?
unfortunately i've only a bunch of *.svg files with the rambo 1.3a schematics. you need to install inkscape to view them... and there are still some questions remaining.
from the pins.h file from the firmware source, you can see following pins assigned to control the lcd:
#define LCD_PINS_RS 82
#define LCD_PINS_ENABLE 18
#define LCD_PINS_D4 19
#define LCD_PINS_D5 70
#define LCD_PINS_D6 85
#define LCD_PINS_D7 71
but the given pins are "arduino pins", so we have to translate them to cpu pins first to check the connection between atmega2560-cpu and the 10 pin connector (P1).
so the pins at the processor are the following:
name -> cpu (I/O)-> 10pin_connector:
RS -> pin#48 (PD5) -> pin#04
EN -> pin#46 (TX1) -> pin#03
D4 -> pin#45 (RX1) -> pin#05
D5 -> pin#29 (PG4) -> pin#06
D6 -> pin#27 (PH7) -> pin#07
D7 -> pin#28 (PG3) -> pin#08
if you once saw some english text at the lcd, it's a good chance that one of the pins at the cpu isn't soldered perfectly and you've got a bad contact there.
recommended way to check this is: "free" the rambo board of every connection, except the lcd cables and the power supply.
power it up and try to press with your finger at the cpu and do a reboot.
helpful may be some cooling spray as well.
if you "free" the rambo completely (get it out of the electronics enclosure), you can check the board for bad solder junctions at the connectors as well.
I wouldn't recommend this to complete newbies, but from your answers and responses I've the feeling that you know what you do 
Re: New Assembly from MK2S Kit -- Garbled Display
You are sure you didn't swap them? So that 1 is connected on socket 2 and vice versa. That the reset switch below the extruder is not working seems to me an indication that your wiring is wrong.
Re: New Assembly from MK2S Kit -- Garbled Display
You are sure you didn't swap them? So that 1 is connected on socket 2 and vice versa. That the reset switch below the extruder is not working seems to me an indication that your wiring is wrong.
I did swap them--meaning I had the originally connectors arranged properly at the LCD but backwards at the RAMBo. Now they're correct at both locations.
At first, before I switched them, nothing was displayed at the LCD. I checked the cables, switched the connectors so that they are now presently correct, and the result is the display shown in the video.
Re: New Assembly from MK2S Kit -- Garbled Display
This thread seems to be related....kind of:
http://shop.prusa3d.com/forum/prusa-i3-kit-building-calibrating-first-print-main-f6/garbled-lcd-display-t2867.html#p22286
Looking forward to any suggestions toward a final solution....
The 10.5 weeks from order confirmation to delivery was very long! Having the assembled unit in my hands is not making my self control and patience any stronger 😀
Re: New Assembly from MK2S Kit -- Garbled Display
➡ there seems to be a bad connection of at least one wire. either at the crimped connector, or inside the ribbon cable itself.
try the following: swap both ribbon cables (use the "|" marked for connector 2 / EXP2 and the "||" one for connector 1 / EXP1).
does this change anything ?
dem inscheniör is' nix zu schwör...
Re: New Assembly from MK2S Kit -- Garbled Display
➡ there seems to be a bad connection of at least one wire. either at the crimped connector, or inside the ribbon cable itself.
try the following: swap both ribbon cables (use the "|" marked for connector 2 / EXP2 and the "||" one for connector 1 / EXP1).
does this change anything ?
Unfortunately no. Switching the cables gives the same result.
When I first chatted with Pavel on the live chat, I offered to check the conductivity of each conductor--they all came back less than 1Ω. I could not get any of the conductors to reliably change resistance by bending the cable.
How else can I check to make sure the cables are ok?
Should I start inspecting the connectors?
It's interesting to me that the incoherent text on the screen is consistent.
Re: New Assembly from MK2S Kit -- Garbled Display
...
Unfortunately no. Switching the cables gives the same result.
...
ok, then we can assume that the cables are ok.
so there is either a shortcut between two of the data pins at the lcd module, a missing connection or the module itself has been damaged.
but usually a damaged lcd shows random garbage... not a steady, repetetive wrong set of characters.
have a look here at the schematics of the lcd2004 module, that i already posted at this thread and that is used at our prusa i3 mk2(s).
so disconnect the module from the cables and check with your multimeter if there is a shortcut between any of the pins at connector EXP1.
if you can't find a shortcut there, check the 16 pins of the LCD panel itself for a shortcut between neighbouring pins.
if no shortcut could be found, check the connections between pin#11 to pin#14 with connector EXP1 pins#5 til #8.
by the way:
I'm familiar with power supplies and motor controllers... Of course stepper motors are capable of back-feeding fairly high voltages, but I assume that the stepper supplies are isolated? Hey, what do I know.
the protection diodes inside the stepper driver feed the generated power back into the +12V line... and the +5V for the LCD (and the rest of the rambo) are derived from the +12V with a step down converter. so as soon as you "generate" enough power by mechanical forcing movement at the steppers, you'll resurrect the rest of the printer.
the different +12V terminals at the psu all provide the same supply. there's no isolation between them.
dem inscheniör is' nix zu schwör...
Re: New Assembly from MK2S Kit -- Garbled Display
ok, then we can assume that the cables are ok.
so there is either a shortcut between two of the data pins at the lcd module, a missing connection or the module itself has been damaged.
but usually a damaged lcd shows random garbage... not a steady, repetitive wrong set of characters.
Oddly enough, The LCD has consistent distorted output with both cables...
have a look here at the schematics of the lcd2004 module, that i already posted at this thread and that is used at our prusa i3 mk2(s).
Thanks for the schematic, this is very helpful.
I can confirm that the LCD unit tests out ok--no inappropriate shorts and the header pins to the connector are just fine.
I liked your explanation on the other page with the cables, I was also surprised to see the red conductor as pin 10.
But hey, one less bend for these cables!!!!
by the way:
...
the different +12V terminals at the psu all provide the same supply. there's no isolation between them.
Yes I can confirm this 😆 it was a funny moment when I first had the printer assembled and the display wasn't working. I unplugged the printer, started moving it off my workspace, then BAM the display flashes! "Oh yes, the steppers..."
Two more important thoughts:
Like I wrote before, I did check the individual cable conductors. I had a test pin shoved deep inside the connector but still I got consistent conductivity for both cables.
Here I am assuming that the cables are fine, yet I actually did see English when I moved the display around (and also did a rain dance, 3 'Hail Mary's', etc.).
Is there something I'm missing?
Thanks for the help.
Re: New Assembly from MK2S Kit -- Garbled Display
that's really an odd behaviour and I'm running low on ideas here.
the problem might be located at the lcd module, the rambo or the cable.
I know that cables beyond 90cm length will cause problems... but usually these problems are related while reading an SD card.
if you have the chance to get your hands at one or two shorter 10pin ribbon cables with attached connectors, it would be of interest how the display behaves when you use the shorter cables instead.
ah, still one idea left:
can you check the connections between the atmega2560-cpu and the 10 pin connector at the rambo ?
unfortunately i've only a bunch of *.svg files with the rambo 1.3a schematics. you need to install inkscape to view them... and there are still some questions remaining.
from the pins.h file from the firmware source, you can see following pins assigned to control the lcd:
#define LCD_PINS_RS 82
#define LCD_PINS_ENABLE 18
#define LCD_PINS_D4 19
#define LCD_PINS_D5 70
#define LCD_PINS_D6 85
#define LCD_PINS_D7 71
but the given pins are "arduino pins", so we have to translate them to cpu pins first to check the connection between atmega2560-cpu and the 10 pin connector (P1).
so the pins at the processor are the following:
name -> cpu (I/O)-> 10pin_connector:
RS -> pin#48 (PD5) -> pin#04
EN -> pin#46 (TX1) -> pin#03
D4 -> pin#45 (RX1) -> pin#05
D5 -> pin#29 (PG4) -> pin#06
D6 -> pin#27 (PH7) -> pin#07
D7 -> pin#28 (PG3) -> pin#08
if you once saw some english text at the lcd, it's a good chance that one of the pins at the cpu isn't soldered perfectly and you've got a bad contact there.
recommended way to check this is: "free" the rambo board of every connection, except the lcd cables and the power supply.
power it up and try to press with your finger at the cpu and do a reboot.
helpful may be some cooling spray as well.
if you "free" the rambo completely (get it out of the electronics enclosure), you can check the board for bad solder junctions at the connectors as well.
I wouldn't recommend this to complete newbies, but from your answers and responses I've the feeling that you know what you do
dem inscheniör is' nix zu schwör...
Re: New Assembly from MK2S Kit -- Garbled Display
Well, I wish I had a dramatic story to tell of how I fixed my printer. But I don't.
Jeff, thanks for the schematics. I looked for those right when I first had problems (and I didn't find them) but I realized that I was getting a little too far ahead of myself. Vielen Dank!
I took the Rambo out entirely, gave the processor a nice squeeze into the board, checked all the connections between the processor and the connectors (they checked out fine), then assembled it all together and it worked. Took some time but it's all working.
Since the only real thing I did was press the processor into the PCB, I think my original suspicion and what you also mentioned Jeff may have been true. Perhaps the processor wasn't well connected to the PCB.
Now I'm focusing on fine tuning the system. I'm getting good printing results, but I'm not getting good results with overhangs. If anyone has recommendations for resources I can go through to learn more about the system so I can tune better, let me know. Thanks guys.
Re: New Assembly from MK2S Kit -- Garbled Display
If the the problem comes back it could be from capacitance on the wires or stepper inductance which can be identified by posting a photo of the wave form. You can pick up fully assembled mini oscopes for $20 (google for DSO 138, https://www.thingiverse.com/tag:DSO138/page:1 )
Re: New Assembly from MK2S Kit -- Garbled Display
Just found out they also sell logic analyzers for $6 that can view the actual data on the lines.... see this vid
Re: New Assembly from MK2S Kit -- Garbled Display
I just found out you can use a web browser and a cheap arduino to debug the data going to the LCD:
http://www.instructables.com/id/Arduinolyzerjs-Turn-your-Arduino-into-a-Logic-Anal/