MAX719 modules bricking

All, I had a working LED matrix panel that uses one of those little MAX7219 boards that has the chip, capacitors and resistor plus the headers. Really simple, running off an arduino nano, with a fully working sketch, no issues.

So yesterday I plugged it in again (it's part of a flight sim cockpit) and it wouldn't work, with either nothing being lit or all being lit. Nothing at all had physically changed. I have a couple more of the MAX7219 modules, so I tried those, with the same result.

So to troubleshoot, I have got one of the example sketches, and simply connected an 8 x 8 LED matrix module direct to the board, and tried that. Nothing at all, and all three MAX7219 modules appear bricked! it's virtually impossible to get the wiring wrong, and when you connect them all the LED's come on, and stay on except for dimming after 30 seconds or so. Nothing else happens,even if I press the reset button on the Nano, and the only thing that has any effect is pulling the USB plug out of the Nano, waiting a few seconds then plugging back in, and all that does is light all the LED brightly again.

I'm bemused, as I really have changed nothing at all, and can't get anything working even with simple stuff. Are MAX7219 chips so sensitive? Even so, I don't remember any loose connections, and even if there was it would only have been to one of the LED's - surely that shouldn't brick them?

I'm looking for any advice or troubleshooting tips that I can get, as I'm assuming that it would be the MAX7219 chip itself that would fail and the capacitors and resistors should be OK? I didn't notice anything getting hot, or electrical smells, power was exclusively through USB and the LED's work fine with no short circuits ( I checked it out)

Any advice or experience you can share gratefully received

Cheers

Les

Can't say I have had troubles myself.

Were these the FC-16 or the older difficult-to use module?

You sure you didn't unplug the display and put it in the wrong way round?

Lesthegringo:
So yesterday I plugged it in again (it's part of a flight sim cockpit) and it wouldn't work, with either nothing being lit or all being lit.

Either or? That is a strong hint.

Lesthegringo:
it's virtually impossible to get the wiring wrong,

But very easy to have a faulty jumper lead which would cause the "either nothing being lit or all being lit".

Apologies for maybe not being clear - the only re-connection was the five pin Dupont header that connects the MAX7219 module to the Arduino - the rest of it is essentially interlocking PCB’s and therefore cannot be mis-connected, although a weak connection is also a possibility. Maybe if I took a photo it would help

The either ‘being lit or not being lit’ part was when I disconnected the Arduino USB cable, not any of the connections on the panel the MAX7219 module was fitted to

edit

Here’s a photo showing how it fits together, the MAX7219 plugs directly into headers on the middle pcb, which then has traces that take the rather illogically laid out contacts from the module to the matrix board below it. The MAX7219 module can only fit one way

Cheers

Les

20200622_163228.jpg

Fascinating board!

OK, I would be seriously checking that "Dupont" cable. :roll_eyes:

If the LED’s all light when the MAX7219 module is powered, can I take that as a sign that the MAX7219 chip itself may not be blown? It would mean that I would not have to wait the few weeks everything takes to get here until I receive replacement ones

Here’s a picture of the other side of the panel in case you were curious

Les

20191223_113046.jpg
Ah, I get it now! You are - as I so frequently advise - using the old and inconvenient MAX7219 module as a convenient mount for the MAX7219 to connect to your large array.

Yes, the observation that all LEDs light or none implies that the MAX7219 is effectively multiplexing the display but is failing to be initialised which implies that a connection is missing in the cable. I always advise putting a 22k pull-up resistor (or is it pull-down?) on either data or clock lines to prevent the MAX7219 responding to random interference while the Arduino is booting and not controlling the lines, so that it does not start up in Lamp Test mode or something similar - which it generally does when the lines are floating. :astonished:

:roll_eyes:

Thanks, will try it

The code for the original sketch remains unchanged, so it must be something introduced elsewhere. I'll put a resistor in as suggested and make a new patch cable. The annoying thing is it all worked, then just stopped working with no obvious cause

Cheers

Les

Pleased to report success, it was as you correctly surmised, the connector cable. I had (rather perfunctorily) checked it for continuity earlier and it seemed to be OK, but when I checked it a bit more thoroughly when it was flexed the resistance changed. A bit more research showed that the wire was separated right at the edge of the connector pin crimp, but the crimping on the insulation held it together.

Of course, when I tested it I laid the cable flat and held it down with some heavy objects as I only have two hands, so must have just made the broken bits of wire touch while doing so. So once I released the cable, the joint opened again so my ‘good’ cable was anything but.

Thanks very much for the assistance ( and the perspective), it’s now working and back in the console.

Cheers

Les