GLCD Only Functioning Correctly with USB Connected

Machine: LAYZOR K40 Conversion

Board: Cohesion3D Mini with GLCD Adaptor

Firmware: Smoothie

Problem/ Question:

I have moved my fully functioning Cohesion3D Mini setup from my K40 during a LAYZOR conversion build. In the process I now have a dedicated 24V power supply which is powering only a fan and the mini.

What I am finding is that if I start the machine without USB connected to my PC, the LCD does not function correctly and instead displays this pattern.

If I start the machine with USB connected everything works fine and the LCD displays the Smoothie DRO and menus as normal.

The power is being supplied to the dedicated 24V header and I have measured it while powered on and am getting the required 24V so I don’t believe it is a power issue.

The LCD is a standard RepRap Discount Full Graphic Controller, not sourced from the Cohesion store however I have tested it also on 3D printers and it works fine there (and of course it is working when the USB is connected to the Cohesion.

Note also that even with the USB not working correctly, if I then subsequently connect the USB, while the LCD stays corrupted, I can fully access the Cohesion through Pronterface and perform normal operations, so the board is running.

I’ve tested with shorter cables for the display but since it does work when the USB is connected this seems unlikely to be the issue.

Any ideas would be appreciated. While I can still use the system tethered, which I will do most of the time anyway, when doing maintenance it can be very useful to have the stand-alone DRO.

You seem to have tested a few things already which is good!

I’d double check all the ground connections. As that’s one of the things the USB might fix.

The other option is some of the headers/jumpers on the board related to the USB connection.

If you add a couple of pictures of your mini and glcd with wiring we’ll be in a better position to assist :slight_smile:

Just to note that when USB was connected it was to my laptop which was not connected to mains at the time. The power header is connected back to the dedicated 24V supply and the K40 header has the ground and laser fire connections back to the K40 supply. I have tested ground continuity between the power supplies and it is present. The Cohesion itself is mounted on a separate acrylic piece that is electrically isolated. Here are some pictures, apologies it is pretty tight quarters in the LAYZOR design.

Hope that helps. Let me know if I can provide any other details.

I remember this happening occasionally back in the days of the C3D Mini - it has to do with having a clean source of 5v on the board to boot the GLCD properly. It would sometimes happen the exact opposite way too - the 24v PSU was good, but a USB port couldn’t provide enough power and the scrambling was from that.

So everything you said points to your 24v PSU in the new installation being the new factor causing this - try a different 24v psu for kicks? Or just hot start with the USB cable and leave it plugged in

The other option is cabinet noise going onto the wires, in which case I might recommend to wrap the GLCD cables with aluminum foil.

Are you confident that your machine is well grounded?

I’ve now tested with another 24V power supply, separate from the LAYZOR, so basically as though I was testing the Cohesion on its own with a 24V supply. I get the same result unfortunately. In terms of grounding, here in Australia we have a dedicated ground prong on our outlets and staked ground. I have checked ground continuity and it is definitely all grounded.

In terms of noise, I doubt that is an issue since in this latest test with the alternative 24V power supply the LAYZOR wasn’t even on or connected. I tend to suspect the regulator on the Cohesion3D Mini, since I assume if the USB is connected then it passes 5V straight through and if not the regulator is used, much like on an Ardunio.

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