Zonestar Prusa i3 Power / LCD Flickering

Hey all, first of all i'm new to this forum so hello, I'm Tony from Scotland, only been printing for 1 day (building printer for 2 days). Purchased my Prusa i3 primarily to print parts for my RC hobby so im not new to electronics / building etc.

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.

Maybe the wires are not making proper contact or the diameter is too small? Since you're into rc stuff, you can use those flexibe high current wiring from the psu to the board, and from the board to the heated bed. Make sure the connectors are tight. If you have a milliohm meter you could check where the voltage drop occurs andvreplace and check wires, solder joints and connectors. Is the psu powerful enough?

thanks for the input imqqmi, the PSU is rated at 12V 20A, I replaced the PSU to Melzi power cables last night with 30A high current wire and checked all the connections. All seem tight and in good contact. Still having problems. It will print first couple of layers without a problem, then the LCD starts flickering again and eventually will crash and reboot. Prints fine with the bed turned off, but the LCD does still flicker occasionally.

I haven't measured across the extruder and bed power supplies yet though, that is a good suggestion which I will try tonight.

I had the exact same behavior and it turned out that the heat zinks on the PCB is to small so the MOSFET's get to hot. I put a fable fan in front of them and now it works fine, I guess I'll print a holder for a small 12V fan at the PCB when I can..

Sounds like a loose power connection to the board, which when the bed is on and using lots of current, the loose connection can't keep the voltage up.

Try wiggling the board while watching the display.

Quote
langassve
I had the exact same behavior and it turned out that the heat zinks on the PCB is to small so the MOSFET's get to hot. I put a fable fan in front of them and now it works fine, I guess I'll print a holder for a small 12V fan at the PCB when I can..

The heat sinks too small or the MOSFETs have not been (over)dimensioned properly. Replacing them with one with a lower Rdson at Ugs = 5V MOSFET, it won't get as hot and probably don't even need a heat sink. The part number printed on the MOSFET can be searched on google and you'll find the data sheet with all the relevant data. MOSFETs also prefer to be driven by pulses, so one could use pwm so that at least 10% of the time the MOSFET is turned off. I use pwm of 127 (of a max of 255, MAX_BED_POWER 127) on a 12V MK2a with 24V. The current stays under the 11A max for the polyfuse and the MOSFET doesn't overheat.

Still it's strange that the LCD flickers if the MOSFETs get too hot, unless they're chinese knock offs that shorts the gate to ground or something, and intermittently at that.

Is there any possibilites changing the heatsink ? thanks

I will try changing the power cable with higher rating first and see what happen

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 circuit has an issue on the Melzi Board
this seems to have affected some boards in the OCT NOV timeframe

If you put a 30-100 ohm resister inline on the wire of the Y-stop this will fix the problem.

There is a capacitor discharging with out the resistance causing the issue.

I attached a pic of the fix, this was just a quick test
attach resistance to the usually yellow (middle stem)

We tested on a few boards and this did indeed solve the problem

If you make the fix let me know how it worked for you

Dino
3D Print Amazing.com

Hello 3Dprinting amazing,

Are you sure that is the issue?
My board was marked OCT 15
I had this issue when I first started using my printer, and found it to be very annoying.
I found out that after I cleared my USB cable from crossing it with my monitor's VGA cable, all came to a stop (the flickering)
so now I run my USB cable directly to the printer without crossing anything else.
but I will keep your fix if ever the issue resurface.
BTW, This "NEW" boards are Melzi V3b which comes with three pins of all endstops.
do we know what voltage it is operating there? -S+

Thanks a lot for your help!!!

HI Bobini, thanks for your hint. I have also the Melzi V 3.0 probably. I checked all the voltages and they are ok. At this time I figured out that the voltages on the endstop pins are 12 V you can check it too, if you have a look at PCB layout on the back. In my case the LCD is not flickering, but a red LED in the middle of the board is blinking, seems that it would like to tell me something... Meanwhile I think I have shot down the Atmega and I tried to move and adapt the firmware to a Ramps board with Marlin. I made a first test print yesterday . It works, but I have to optimize the Slicer settings. It seems to be a long way...

Kindly Regards
Bernd

Well, if led is blinking, did you try to reload the firmware?
Make sure the pins that allow the download needs to be shorted! And the power is selected from USB.....
Not sure if this info is too basic to you, but hope this help

And thanks for letting me know about the voltage!

Hi bobyni, the board was blowing up by playing around with the endstops....

Bernd

Thanks for the input, and I will need to give the resistor on the ystop a shot, I have some laying around and I will solder one onto the Ystop yellow wire.

I did however find another solution. I figured if the Melzi is powered through the USB lead (by plugging in USB to a computer, and changing the jumper selector to USB on the Melzi) then the printer works perfectly. The heatsink and voltage regulator seem to remain stable and screen stays powered. I've been printing now for 2 months with this solution without any problems!