I had on the bench this Aliens PCB:
Board had sever sprites issue:
I performed a MASK ROM check which reported two bad 4Mbit devices @K2 and @K8:
I was able to exactly reproduce the issue by using two dummy ROM files in MAME:
So, without further delay, I went to remove these devices and install two 40 pin sockets for the 27C400 EPROM replacements:
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:
Probing the 2Mbit MASK ROM revealed no activity on data and address bus, all pins were stuck high so I removed it:
and replaced it with a 27C400 (with doubled content since no 2Mbit MASK ROM replacement exists).This restored all sound samples.End of job.
2 Responses to “Aliens repair log #1”
Sorry, the comment form is closed at this time.
How do you insert the “dummy ROMs” into MAME? I’m guessing it isn’t a straight swop of rom in mame to dump?
Yes, it’s a ROM swap.You have to create empty ROM files of same size of original ones and replace them with these.I use a little program called Dummy File Creator: