Sunday, 30 May 2021

Metamorphic Force repair log

Got a Metamorphic Force PCB for repair :

The board was in very good overall shape but, when I powered it up, I got only a solid black screen,no video output.Checking with a logic probe the RGB colors revealed they were inactive :

The 68000 main CPU was running so I made some check with a video probe (a simple device that can display data on screen by using one of the RGB colors, in my case I used the GREEN one).I went to touch with the probe the GFX EPROMs and I got parts of graphics displayed on screen :

In this way I was able to figure that out the board was actually alive but playing 'blind' (with no sound, too).The final stage of the RGB colors generation is accomplished by some DACs in form of custom SILs marked '054573' (plus the '054574' that acts as filter/mixer).They converts into analog the digital signals of the '054338' custom ASIC (in QFP160 package) that receives, in turn, the digital bits from the three palette RAMs.

The outputs of the '054338' to the custom SILs were obviously inactive but also many of the inputs were in same state.Looking at Lethal Enforcers II schematics (which run on System GX hardware but shares same design) I figured out the '054338' receives some color bits from the '055555' custom (in QFP208 package) :

On schematics these signals are labeled 'PCOL' :

Probing them revealed they were all stuck so likely the chip was faulty.Having some spare I decided to replace it :

 The spare was soldered and area was cleaned from flux :


At power up I was finally greeted by the POST screen, the '055555' was really bad :

Board successfully booted, game was fully playable but, as previously said, the sound was missing at all :

Obviously my first suspicions fell on the '054986A' hybrid audio module which was in rough state :

I could have tried to replace the electrolytic capacitors on top but I settled things once and for all and opted to replace it with a reproduction of mine.The original module came off quite easily using hot air :

The reproduction was installed on a pair of header pin strips :

This gave sound back to this cool game.Board 100% fixed and another repair successfully accomplished.

1 comment:

  1. Fantastic work. I have this PCB and I suspect need repair module sound will soon.