one_eternity_later.png
Today I made some progress !
I found that "@" pattern strange, and the pattern I saw in my own game also makes me thinkg there's a stuck bit in the RAM.
Since the RAM was fine, all there was left to check were the data lines just like @root42 told me.
So I took a schematic of the 4464 RAM chips, I fired up my meter in ohm meter position and started tracing.
This is what I came up with :
RAM_traces_1.jpg
The red traces I draw are the one I checked with my meter. The blue one is one that *should* be there but isn't. It looks like I'm on the right path 😁
So I checked the unconnected pin on the chip and checked where it was going.
On the back of the card, I found this trace :
RAM_traces_2.jpg
(Red is the visible part of the trace, blue is where the trace goes after the via). Bingo, that's exactly the data pin I was suspecting, it's D2 on the second chip.
And check this out !
RAM_traces_3.jpg
Yeah that looks bad.
Now what's really strange is the break in the right circle I drew ... It looks like a misprint from the factory 😮. Was this card considered as defective since its creation ?
Time to bodge !
RAM_traces_4.jpg
And ??
Epic fail sound
Now that's weird, because that thing really looks like a memory error, how fixing a trace for a data line that was definitely broken wouldn't fix anything ?
Then after talking to other people, they suggested me to test the snake game again, because maybe the character ROM I burned wasn't the right one.
Could this be it ?
Let's try it out !
Hey that looks correct now !!
So my fix actually fixed something, but it seems this card has other problems (now that I think about it, maybe the ROM I flashed is fine, but the data lines between the ROM and the paradise chip are also faulty ?? I'm gonna check that right now !!). I made some good progress today 😁
Edit : all traces between the ROM and the controller seem good, so I guess the flash is just wrong. Does anyone have a character ROM from a paradise PVC4 card ?