[REPAIRED] Pac Mania RAM2 ERROR 0000

[Tailsnic Retroworks]

Hi. I'm trying to repair a Pac Mania with this error. I have desoldered the 2 rams located on E6 and D6, and they are working perfectly. The first byte line is 0000, but I don't know where to search next to this information.

 

[ShootTheCore]

If you have a logic probe, probe the address lines on the two RAM chips while the startup diagnostic is executing. You’ll likely find one or more of them are stuck High or Low with no activity. Follow the stuck lines to their sources. Odds are that they’re being driven by TTL logic chips (smaller chips whose part numbers start with 74) that handle memory mapping. It‘s common for a TTL chip to fail such that it’s Inputs are triggered but one or more Outputs do not. The diagnostic routine then flags a RAM failure since the failed TTLs don’t set the RAM addressing properly.

 

[ShootTheCore]

The schematics for Namco System 1 are here:
https://www.arcade-museum.com/manuals-videogames/P/PacManiaSP3151stPrintingSchematicPackage.pdf

Page 12 of the schematics cover the Object Control RAM chips at D6 and E6. The memory addressing is handled by the two TTLs at H6 and L6 - their outputs feed into Custom 48, and then come back out of Custom 48 into the RAM. Custom 48 controls the Output Enable OE and Chip Enable CE lines for the RAM. Both OE and CE must be enabled for the RAM to process anything. Pin 59 on Custom 48 is important too - it controls whether the RAM is reading or writing data with the Read Write Enable RWE line.

i suggest using a logic probe to probe the OE, CE and RWE lines on each RAM chip first for activity. If one line doesn’t show activity then check continuity for the line between the RAM and Custom 48. If continuity is good then Custom 48 may be dead - a replacement will have to be sourced from a parts donor.

if the OE, CE and RWE lines do show activity then probe the Address lines where they come out of the TTLs and go into Custom 48 for activity. If you’re lucky, one of those TTLs has failed, causing one or more of the address lines to stick and the addressing to be incorrect. Note that the A11 and A12 lines on the RAM are tied to Ground and thus it’s normal for them to always read Low. If the addressing looks good going out of the TTLs into Custom 48, but bad coming out of Custom 48 into the RAM then Custom 48 may have failed.

 

[Tailsnic Retroworks]

The schematics for Namco System 1 are here:
https://www.arcade-museum.com/manuals-videogames/P/PacManiaSP3151stPrintingSchematicPackage.pdf

Page 12 of the schematics cover the Object Control RAM chips at D6 and E6. The memory addressing is handled by the two TTLs at H6 and L6 - their outputs feed into Custom 48, and then come back out of Custom 48 into the RAM. Custom 48 controls the Output Enable OE and Chip Enable CE lines for the RAM. Both OE and CE must be enabled for the RAM to process anything. Pin 59 on Custom 48 is important too - it controls whether the RAM is reading or writing data with the Read Write Enable RWE line.

i suggest using a logic probe to probe the OE, CE and RWE lines on each RAM chip first for activity. If one line doesn’t show activity then check continuity for the line between the RAM and Custom 48. If continuity is good then Custom 48 may be dead - a replacement will have to be sourced from a parts donor.

if the OE, CE and RWE lines do show activity then probe the Address lines where they come out of the TTLs and go into Custom 48 for activity. If you’re lucky, one of those TTLs has failed, causing one or more of the address lines to stick and the addressing to be incorrect. Note that the A11 and A12 lines on the RAM are tied to Ground and thus it’s normal for them to always read Low. If the addressing looks good going out of the TTLs into Custom 48, but bad coming out of Custom 48 into the RAM then Custom 48 may have failed.

Hi!! Many thanks for the help. The custom 48 is in good shape because I exchanged it with another Pac Mania I have, so it's good. I'll check those TTL's (I'm afraid TL866 mini can't check LS365).

EDIT: one of the two LS377 resulted bad. Replaced it and still ram bad. I'll have to wait for the TL866II Plus for checking the two LS365.

 

[Tailsnic Retroworks]

Repaired!!!! One of the two LS365 where bad!!! Many thanks @ShootTheCore !!!!!

 

[ShootTheCore]

Huzzah! Glad you got it working!!