Dec 272015
 

I had on the bench this Aliens PCB:

Aliens_PCB

Board had sever sprites issue:

sprites_issue

I performed a MASK ROM check which reported two bad 4Mbit devices @K2 and @K8:

MASK_ROM_check

I was able to exactly reproduce the issue by using two dummy ROM files in MAME:

0001

So, without further delay, I went to remove these devices and install two 40 pin sockets for the 27C400 EPROM replacements:

sprites_MASK_ROM_rework

With these replacements fitted sprites were perfect but I noticed that sound samples (like voices of main character or enemies) were missing:

Sound samples are stored in a 2Mbit MASK ROM @D5 (which is not checked by the self-test) and its data are processed by a custom marked ‘007232’ which is a PCM controller:

007232&MASK_ROM

Probing the 2Mbit MASK ROM revealed no activity on data and address bus, all pins were stuck high so I removed it:

MASK_ROM@D5_removedJPG

and replaced it with a 27C400 (with doubled content since no 2Mbit MASK ROM replacement exists).This restored all sound samples.End of job.

 Posted by at 9:12 pm

  2 Responses to “Aliens repair log #1”

  1. How do you insert the “dummy ROMs” into MAME? I’m guessing it isn’t a straight swop of rom in mame to dump?