NBA JAMZZZZ Repair help

[esqueleto]

I recently picked up a new PCB that has a few issues (as Pictured). these same vertical lines (horizontal black bars are scan lines picked up by my phone) appear during eprom check. I've installed a new WILLIAMS PLCC ROM VER 1.5 as well a set of NOS eproms, no change. I noticed some corrosion a few components near the edge of the pcb (i may focus efforts there next). Just wanted some advice as to what may be causing this.

 

[Phil Bennett]

Bad video RAM or buffers in that area I imagine. What does the PCB test show?

 

[esqueleto]

I'm not sure, it's hard to read what the startup test is telling me!

 

[Phil Bennett]

UA11/UB11 and UA13/UB13 are testing bad. Perhaps a signal common to these two pairs is bad rather than the RAMs themselves.

 

[Moblin]

Anybody find the schematics on this? I tried but no luck so far...

Edit: Got it! I only put 3 Zs instead of 4...

 

[gamefixer]

is this another one of those boards with caps that leak?

 

[Phil Bennett]

is this another one of those boards with caps that leak?

Not as far as I know. Video RAM related errors are fairly common though.

 

[mecha]

are there buffers that go bad or something? they have 74LS374s on them, those ever go bad?

 

[esqueleto]

FIXED, so to walk it back a little bit, after Phil suggested the UA/B 11/13 sharing data I busted out the schematics and sure enough they share 3 adresss lines going straight into UE9 a 74ls541. I check for broken traces and what do I find... a bridged connection! I separated the pins and boom, fully working JAMS... thanks guys. Funny thing is I looked over this pcb 3 times and didn't see that. Time for some new nerd googles I guess!

 

[Broodwich]

What is the Jams or Jamzzzz you keep referring to?

 

[esqueleto]

It's the new hotness, I picked it up at Walmarts, they might have it at Targets now too.

 

[mecha]

What is the Jams or Jamzzzz you keep referring to?

I think there was an FS and that was the title a few days ago.

and this is a pretty common thing with T-unit boards. it's typically caused by maroons that take the plastic feet off. added bonus if they operate the boards on carpet.