Pole position ram 28 error

[Lurch666]

So after fixing a pole position I decided to do another one. Since I now had working boards how hard could it be?
At first it was not booting which was solved by replacing the pal with a gal at 7C.
Then it booted to a ram 6 error which was solved by replacing the ram at 7J.
Now it booted to a ram 0 error. This was fixed by replacing the 2114 at 8F on the video board.
Then it gave a ram 30 which was the ram at 3E so I replaced that.
Now the game was booting but with messed up graphics which were smeared across the screen. While looking for that fault (which turned out to be a bad LS174 at 8L on the video board) it started to boot to a ram 28 error which is the ram at 3F.

So I replaced the ram at 3F on the video board but that's made no difference.
I have checked continuity for the ram chips and checked all the logic in the video sync chain,control signal converter,video ram address controllers and the playfield video memory. I can't see any other part of the video circuit that could affect this ram. If I plug in my good video board the game boots so it's not an issue with the CPU board. I've cleaned the edge connectors,checked voltages and swapped out all the custom chips.

I'm really running out of ideas now. Can anyone suggest where to look?
It's annoying because I fixed the graphics issue but this ram 28 error is stopping me from seeing if the graphics are fully fixed.

 

[Mr20to5]

From your other thread, did you look up my fix log on my blog. Honestly, we spent so long chasing ram error after ram error. Ended up removing and replacing every single socket and it all worked fine after that.

 

[Lurch666]

I did read that thread but this issue is on the video PCB and most of yours is about the CPU PCB.
I have checked the continuity of the sockets and they seem fine. Might just change them out since I'm running out of things to test. Everything appears OK so I don't understand why I'm still getting this error.

 

[Mr20to5]

Yeah, sorry, I didn't mean the specifics, it was more how we were just chasing ram errors and ghosts, getting nowhere, but changing out the sockets got rid of that and let us get on with real issues.

Tedious as hell though, but good luck.

 

[favouredson]

I had a Xevious board with a falsely reported RAM error.
After much checking and probing, it turned out to be bad connections on one of the Namco custom ICs.

 

[Lurch666]

So replaced sockets at 3E and 3F (didn't replace the ones at 4E and 4F since the system detects when these rams are missing and I had run out of 24 pin sockets).
Replaced the sockets of the customs at 4D,2F and 7E.
Replaced the LS245 at 5E since that handles data to the affected ram and also swapped out the LS245s at 6H and 6F since these used the same data lines as the one at 5E and I figured it could be causing contention.

Nothing has cleared the RAM 28 error.

Thinking of swapping out the chips at 5B,5C,5D and 5H since these are also connected to the same data lines but since they are never activated during the ram test I'm thinking this won't make any difference either.