CPS2 Work RAM NG

[fluxcore]

I've got a CPS2 b-board which has developed a fault, boot up RAM test screen shows some garbage and 'WORK RAM NG', gets no further than that text.

I can't seem to find any mention online on just what comprises the work ram in the CPS2 system though - only mentions I see are of the 6264s being the object RAM. There don't look to be any other discrete chips which could be RAM though.

Anyone got any technical knowledge which may help? I'm guessing it might be some 74 logic chips failing, or maybe some traces, but would like to have somewhere to start from.

 

[Darksoft]

I'll see if I can check the schematics of the a board but if I understand right, this happens with a regular b board, right?

You need to check not only the rams but also the logic driving it which are usually 74ls which tend to fail with the time.

 

[fluxcore]

I'll see if I can check the schematics of the a board but if I understand right, this happens with a regular b board, right?

You need to check not only the rams but also the logic driving it which are usually 74ls which tend to fail with the time.

Yep, 100% a b-board failure, a-board has been tested working with a different b-board, and the faulty b-board is also faulty on another a-board.

It would be interesting if the work ram is actually on the a-board though, at least that would be helpful in knowing which pins on the b-board to trace around from.

Guess I'll need to poke around with the logic probe... hope it's just some 74ls

 

[fluxcore]

With some tech support from the mighty Leo, who let me know the HM658128 chips on the A-board are the Work RAMs (HM514260 are graphics related), I've fixed the board!


I saw some weird signals on a couple of LS245s in row 10, replaced them to no avail. Poking around the area a bunch more, I noticed lack of continuity between pin 18 of rom 9A and the 10B LS245's pin 8 - there was some corrosion in between the socket and the RA9 resistor array that was almost impossible to see. Patched the trace on the underside of the board, and have restored operation! Huzzah!


WydD's wiring spreadsheet available at https://docs.google.com/spreadsheets/d/1SGXb6cE9Uu68Lmt0O0knL34eWvkaVA7-mJ8i6F27lmk/edit#gid=0 was a big help, although I still needed to pin out the signals (spreadsheet mainly shows functions). I've filled out my own old spreadsheet a bit more, https://docs.google.com/spreadsheet...zsV7GdXjoEBVwbuQa5GsjsCqU/edit#gid=1580050406