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Power / LCD Flickering during printing

Posted by NorcoT 
Power / LCD Flickering during printing
November 02, 2015 04:28AM
Hey all, I just posted this in the Prusa i3 sections but in hind sight this is a better place for it, sorry i'm still finding my way around this forum.

Last week I received my Prusa i3 (cheap Zonestar with Melzi control board and heated bed). Getting a few decent prints already which is nice but i'm having a problem. When printing sometimes the LCD screen flickers on and off rapidly, the printer keeps printing (most of the time) but the backlight and the display flickers. Its especially bad when the printer is doing the infill details where the steppers are all going quickly. I've had a couple of times where the printer has reset mid print while doing this, however not every time.

On preheat, or when printing the first couple of layers there is no fluctuation at all, just when it starts ramping up its speed the flickering comes in. Also the heated bed LED flickers as well, and when looking at the temperature read outs on the LCD screen for the bed they flicker from 0C to the 60C (or whatever the beds at) and continues to do so.

This morning I ran a multimeter across some points as I suspected it was the power supply. While the printer is running, I measured the voltage across the pins on the Melzi board and they fluctuated between ~11.4 and 12v. I then ran the meter off the pins at the PSU itself and they read 12v steady..

So i'm a bit puzzled. Anyone else experienced anything similar before or have any thoughts?

Thanks for any help in advance, its much appreciated.
Re: Power / LCD Flickering during printing
November 02, 2015 01:30PM
If you're measuring a lower voltage at the board than at the power supply then the difference is due to the resistance of the wires, and the drop will be proportional to the current being drawn. It sounds like you could benefit from replacing the power wires with thicker ones to reduce the voltage drop. However, I doubt that a .6V drop in the supply voltage explains what you are seeing, the LCD runs off a regulated 5V supply that won't see the difference between 12 and 11.4 input. From your description I'd be looking for a loose connection that's getting shaken around when the printer is doing short fast moves.
Re: Power / LCD Flickering during printing
November 02, 2015 06:48PM
You mention the voltage but not for how much power the supply is good.
Motors, hotend, heatbed, electronics - they all want their share of the current available.
If your power supply is on the limit it no surprise your LCD plays up.
Re: Power / LCD Flickering during printing
November 03, 2015 04:00AM
Hi guys thanks for the input. So last night I replaced the PSU to Melzi wires with 30A rated cable, a bit thicker than the original cables.

Tried printing again, without the bed on it prints fine, LCD flickers occasionally but no problems with the print. When I turn the Bed on for the same print, the first 3 layers or so prints fine, then the LCD starts to flicker even when the printer isnt making rapid movements.

I checked the supply, it claims its a 12v 20A supply. Unfortunately I dont have an ammeter to check the current being drawing, and my multimeter only handles up to 15A so I cant check the current draw.

Starting to run out of ideas apart from a dodgy / underpowered supply. Someone on another forum mentioned that he has similar problems, but disconnected the LCD and printed using USB connection.. Can a faulty LCD cause this kind of problem? I will try that out tonight anyway.
Re: Power / LCD Flickering during printing
November 03, 2015 04:21AM
A 20amp power supply does not leave much for the electronics and motors to run once the bed is active.
Get another second hand ATX power supply and use it to power the bed only.
This way the massive draw of the bed won't affect your printer electronics.
Re: Power / LCD Flickering during printing
November 03, 2015 05:24AM
Thanks, I thought 20A was a bit close, if I power the bed from a separate supply I guess it will need its own switch control for the temperature as this is all currently done on the Melzi?

I came across another post somewhere else about the same printer and similar LCD problem. He mentions that it was the 5v regulator on the Melzi, which caused his LCD to flicker and occasional reboot. Then someone else mentions that running the printer without the LCD and using a USB connection sorted his problem..

Could it be that the regulator is having problems when the Melzi is drawing high current from the PSU, and the 5v supply becomes unstable which causes the LCD to flicker and eventually the logic chip to reboot? Does the LCD and its backlight run off the 5v circuit?

I think I will switch the jumper setting tonight on the Melzi and power the 5v circuit using USB and print using Repiter-Host on the laptop. I guess this will bypass the 5V regulator on the board which will tell me if its the regulator causing the problems?
Re: Power / LCD Flickering during printing
November 03, 2015 09:02AM
You might want to read here to check.
If you use a second power supply for the heated bed you just connect a SSR (solid state relay) to the bed output on your Melzi.
The switching connectors of the SSR go between one wire of the power connection to the heated bed.

Melzi switches SSR and uses basically no amps for this, SSR switched heated bed from a different power supply - Melzi is happy winking smiley
Re: Power / LCD Flickering during printing
November 03, 2015 10:07AM
thanks downunder, this is what I suspected. I will investigate the regulator tonight and hope that is the source of the problem. If not I will then look into a seperate or new PSU
Re: Power / LCD Flickering during printing
November 14, 2015 01:26AM
Hi Norco T
I got the same printer from 3D star : Zonestar P802 using the Melzi V"2" board.
and yes, it is the same here as well.
I think, between the extruder and the heated bed, when running all together, it gives issue to flicker.

But, I have seen it to flicker without anything running and that I think has to do with the serial port connected to the PC!
I use Repetier host 1.6
repetier firmware V0.91
Have you solved this LCD issue by putting a 2nd power supply +SSR?

Re: Power / LCD Flickering during printing
December 03, 2015 01:17PM
We use the Zonestar Melzi in a new product we are releasing, as such have seen this issue.

After working with the Zonestar folks it appears that an issue with the Ystop is missing the proper resistance on the Melzi Board
this seems to have affected some boards in the OCT NOV timeframe

If you put a 50 -100 ohm resister inline on the wire of the Y-stop this should fix the problem.

It appears the switch is normal closed drawing current all the while.

We have not tested the solution yet but will in the next few days
If you make the fix let me know how it worked for you

3D Print Amazing.com
Re: Power / LCD Flickering during printing
December 04, 2015 07:39PM

So I added the 100 Ohm to the ystop wire as a quick test (middle position - usually yellow)
Pic attached for reference

This did indeed stop the unit from having the Flickering and power loss.

I am going to research it more as, the middle position is a N/Open
which means the resistor should have no effect while the bed is not at home.

Soooooo.... Im at a loss to explain
Unless they are marked wrong..
If I get a chance I will put a meter on it

But it did solve the problem, no flicker or loss of power

let me know your results....


Edited 2 time(s). Last edit at 12/05/2015 03:05AM by 3DPrintAmazing.
open | download - _Resistor on ystop.png (255.9 KB)
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