Electron Clone v2
The idea behind building v2 was to incorporate the MRB onto the pcb instead of it being a plug in board and to add an SD card reader for MMFS but as the title of this page says I'm not happy with the results. It took a bit of effort to find working parts and that includes the ULA, memory and a good 6502 but once found both versions v2.0 and v2.1 appeared to work normally. I say appear because I found that after being on for about 10 minutes this happens:
Occasionally some pixels will appear while others disappear! and it I happens to both machines. Now these character distortions are stored in screen memory as they scroll up the screen when I issue commands. The new text is ok but over time it will be corrupted too.
I poured over the designs, comparing everything from V1.2, to v2.0 and v2.1. Both the circuits and the PCB tracking looking for some inconsistency but everything checks out ok. So what could I have done wrong?
Well my theory is that moving from a 2-layer board to a 4-layer was a big change and I hadn't considered the consequences. I must admit I didn't pay too much attention to this change, I only had it in my mind by adding power planes I would get a better distribution of power over the full PCB. It did indeed do that but I didn't look at the IC decoupling..I took it for granted that as long as the cappacitors were there they would do their job..I didn't give it a second thought.
Having looked over this part of the PCB layout I'd guess that about 95% of the decoupling capacitors wouldn't be doing their job..shockingly bad layout!! I have gone over each one and corrected their positions and ensured the tracking is as short as possible to each IC.
I am going to give this layout one more build so V2.2 is in the works. I have also fixed the keyboard error I introduced in V2.1 and I've moved the keyboard connectors 0.1" further back to help accomodate the keyboard ribbon cable when using the new slimmer case.
Clones under test..
The corrupted characters scroll up..
The new v2.2 board..looks the same as v2.1 but there's hundreds of tracking changes.
It's now a waiting game.