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Hi again,
After making the 4x4x4 cubes I thought I'd have crack at the big one. All has gone together great. The pcb populated and tested using LEDs in the positive and negative posts and they all light up. Made the 8 layers and tested as I went. (learnt that from the 4x4s). Tested them all with a 3v "coin" battery and everything is fine. Put the first back layer in and tested again with the battery in case anything moved but still all fine. So, took the advice of the guide and put a wire in the positive post and connected it to the first bottom horizontal positive line and ................nothing. Not a sausage, bugger all.
I must be doing something epically stupid and can't see it. It was all going so well.
I'm using the USB line and tried using a battery charging plug and also tried my laptop but still nothing.
Anybody spot my glaring error?
I'm still learning so any help or advice is welcome.
Many thanks.
Stay safe.

The pcb populated and tested using LEDs in the positive and negative posts and they all light up.

I assume this means when you connect a single LED to the PCB it is flickering on and off as it runs though its patterns? If so this is a good sign the PCB is working and it's likely the issue is with the LED grid itself.

Put the first back layer in and tested again with the battery in case anything moved but still all fine. So, took the advice of the guide and put a wire in the positive post and connected it to the first bottom horizontal positive line and ................nothing. Not a sausage, bugger all.

If you've not already can you try removing the grid and connecting a single LED across one of the back layer posts and its power post to check if it does anything. That would help confirm if it's the PCB or the LED grid that has the problem.

After making the 4x4x4 cubes

Just a sanity check, the LEDs on the 8x8x8 cube are connected together in the opposite polarity to the 4x4x4 grid. Just want to check what with building the 4x4x4 cube fist you have got them soldered the correct way around that all.

Hi Andrew,
Thanks for replying. I put together the lattices together as the instructions said. BUT, like a plank, I put the positive LEDs into the posts, like the 4x4s. So, no wonder it didn't work. I flipped it over and put the negatives in and then checked it and it all lit up.
I really should be in a home for the permanently bemused and baffled.
Thanks again and sorry for wasting your time.
Stay safe.

Tel ;o))

Ah well least it was something that's easy to fix.