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System16B PCB Static RAM (Altered Beast)

jwilliams

jwilliams

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Hey all,

I'm hoping some top/smart men/women can save me some time and tell me the best way to source all the static ram ic parts on my 16B. Starting having background scrolling rendering flicker and character sprite flicker. Shinobi self tests fire ram failures on H13 and H15. I just want to machine pin socket and replace all the static ram good or bad with some more reliable stuff. Cause I love SEGA.
  1. TMM2115BP-10 (Qty: 5) RED
  2. HM65256BLSP-10 (Qty: 2) GREEN
  3. TMM2018AP-35 (Qty: 6) BLUE
Did I miss any?

16b-pcb-thumb.jpg


Thanks!
Josh
 
TMM2115BP equivalent:
https://www.arcadeshop.com/i/1476/mb8416a-15l-sk-tmm2115bp-15-sram.htm
https://www.utsource.net/itm/p/1701107.html

HM65256BLSP
https://www.utsource.net/itm/p/912298.html

TMM2018AP
https://www.utsource.net/itm/p/11724248.html

Be aware though that memory addressing on System 16 is handled by 74 series TTL logic chips. If the self-diagnostic is flagging two adjacent RAM chips as bad, it's likely that one of the TTL chips that handles the mapping between those two chips has failed, rather than the RAM itself. Also inspect the area around those chips on the top and bottom of the board and make sure there aren't any scratched or damaged traces.

Ideally, you'll want to connect a logic probe and test the address lines on H13 and H15 to see if one of the lines is "stuck" - ie, doesn't change state during the self-diagnostic test. If so, trace that line back to the TTL that drives it.

I have a tutorial video on using a logic probe to test logic lines that may be helpful. My video covers identifying a bad ROM, but the same principles apply for checking TTL logic and RAM signals.

View: https://www.youtube.com/watch?v=2PAtTIAijeA&t=617s
 
Last edited:
Thanks for that. Hooking up my logic probe right now. I bet I broke something with my big mitts because if I apply any pressure to the board while it's running then the graphical glitches change. Heck, if I even tap my bench the character sprites flake in and out. Hopefully I just need to reflow some joints on a 74 TTL ic.

Josh
 
Some additional questions (System 16B specific):
  1. Are there readable schematics that exist of the 16B PCB? The ones I found in my initial search look like photos taken by a spy and are no where near the detail of the Williams/Atari stuff from back in the day.
  2. Looking for suggestions on best way to use a logic probe ad-hoc on the ICs directly under the ROM board. Doing everything solder side seems unwieldy.
    • Do I need to build some 50-pin extension cables or something?
    • Can the board be powered up without the ROM board attached?
  3. Does anybody know of a more extensive test ROM I could burn that would help?
Thanks again!
Josh
[genesis]
 
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