Hi all, Just received the final parts for my MPCNC project. A RAMBO board from UltiMachine.com and a RepRapDiscount Full Graphic Smart (not too sure about Smart part)Controller. All was good 'till I connected the two using Atom and marlin 2.0 (Ryan’s version). The code runs fine but the problem is that the LCD screen contrast is non existent, very dim. I believe I’ve traced the problem back to the RAMBO board. The VCC output at EXT1 pin-1 is +4.49Vdc. The input to the switching regulator is a solid 5.1Vdc from an modified ATX PSU. Being that the LCD ‘contrast’ pin is very sensitive to voltage and the pot seems to do nothing, I hoping this is the problem. I’ve swapped displays with a known good one and its dim too. The new one works fine on the MKS Base 1.4 board in my printer too.
Has anyone else had this problem too. The WEB is full of guys adding resistors and the such to the display PCB as a work around. I’m hoping that ‘tweeking’ the switcher feedback will bring the voltage up to a solid 5VDC. If not…never mind. I need help. The wirdness of the ‘contrast’ circuit on the display didn’t help. BTY, the VCC on the MKS Base China board is +5.0Vdc and everything is as it should be. I got The display thru Amazon from the cheapest vendor I could find. Built by www.bigtree.com in China. It works just as advertised but not on my RAMBO board. I’ve enclosed a shot of my work so far. I’m a retired EE from Hughes and Rockwell Collins and I can’t stop tinkering with stuff. Doug
Hmmm, that is a new one. I might be able to test one of my boards on Wed to see the voltage I get but if you tried two displays maybe you did get a bad board. Try swapping the cables just to be sure, maybe one has a cruddy crimp or something.
Good morning,
I just tried a new cable set (after shaving the indexing lugs) with the same results, a dim negative looking screen. I’ll look into the sensitivity to voltage of the LCD panel itself this morning. The difference between the RAMBO and the MKS contrast voltage on the LCD panel is as follows. RAMBO +4.49Vdc non-adjustable and the MKS +4.97 also non-adjustable. I really don’t want to mod a brand new RAMBO board and I shouldn’t have to, or go thru the ‘fun and games’ of returning it and wait for a new one. I don’t think that the guys at UltiMachine like me after I complained about receiving an old design with issues (rev LCD sockets) and didn’t furnish any instructions as a work around. Nothing about it or on the WEB. Paid top dollar too! If it wasn’t for your article on your site I’d still be looking for the cause. Thanks much! Onward and upward. Doug
Keep up the good work…
It’s me again,
The simple matter is that the contrast circuit on the display is 5Vdc critical. Most likely it was a simple, cheap design based on they (China) relied that 5Vdc was 5Vdc plus something and minus nothing. In my case any mods to the display won’t get me there. At the moment I don’t know for curtain (looking into it)if the contrast is a function of voltage of current. My guess is voltage. Thus I can’t get there without RAMBO supplying at least +4.97Vdc from a circuit made to supply +5VCC. Screwed.
If I’m wrong, as seems to happen all to often, please someone advise.
Doug
OK I’m done. Rambo board goes back The 5volt VCC is running at +4.47V. While looking at it wondering what to do next, the display popped to normal contrast, wow! The VCC is now 4.91V. Cool. I power the board off then back on. To no surprise it’s back to 4.7 with a dim display. The LCD appears to meet the spec as far as that goes. The only thing can think of I haven’t tried is to load the VCC. I’m testing the board with only +12V, +5 and the display plugged in. I’m running Ryan’s configuration.h file and Marlin 2.0. Crud
OK my bad.Just talked to Johnny at UltiMachine (very helpful). A bit of confusion on my part. My logic input was 5V and should have been 12V to make up for the loss in the switching reg. Simple. Apologizes to all. I must have missed that fact in all the data available on the internet. Anyone made a complete wiring diagram on one of these things and not snippets here and there.
Sweet!
Dang, I do believe Johnny designed the board (I know his company did), I am pretty sure he did the ramps himself. That is a pretty solid email you got there, nothing like having the inventor put us all to shame trying to figure it out.
Ryan, There is so much good information and some miss information on the internet that sometimes it’s hard to isolate the truth. That’s why I use your site as the bible. It stands to reason I guess, you developed the concept first. Just keep it coming, well done. Is there a place on your forum to discuss technical firmware configurations and and the why of things? I’m working up a wiring and connection diagram for a typical MPCNC system. I’ll run it past you if you don’t mind when I’m finished.
Getting older but always learning. Doug
If you have more questions just keep adding them to the list here. Helping you understand why, leads to a more pleasant experience with the machines.