This is the second board Enrico gave me for repair, a Data East game from 1990, the first chapter of the Dark Seal legacy, also know as Gate of Doom, here is the PCB:
After a quick and dirty test, the board is experiencing several issues, wrong/missed colours in the text layer:
The text is unreadable it shoud be bright white, you can see the issue also on this image:
All the text were black, and nasty jailbars were present on the back graphics plane, and as the demo goes on also the sprites plane were totally or sometimes partially missed, and the background reports wrong/missed colours too. You can look at these issues on the following picture:
I started investigating by the usual visual inspection of the PCB. A deeper look at the soder side reveals the first damage reported by the board:
A scratch cutted some traces, it was very thin and sharp so the issue can be fixed by removing the protective shield painted over them and by reflowing the traces with the soldering iron without patch wires over the board:
With my magnifing glass i looked also at the component side of the board, and with the help of a needle a spotted also some lifted pins on a custom IC, also the traces under the IC seems to be lifted but fortunately they were not damaged, so i reflowed them:
These fixes recovered, the text and background colours and the missing sprites ingame:
Now the text is ok, and the sprites and background too :
But, jailbars still there … so the board need further cares. Jailbars can be caused by several issues, a bad eprom, broken traces, broken logic, broken data buffers, and so on … i started looking and the maskrom where the involved graphics are stored following the data path with the scope. Probing around i should able to identify the right maskrom, usually you should look at the schematics, sometimes they are well documented also on the MAME driver source, but when these methods doesn’t work you should get hands dirty and use other uncoventional methods for the series … “don’t try this at home!”. But safety first! So don’t worry Enrico no harm has been done to your board! 🙂
I succesfully identified the maskrom where i must look at, and i found one stuck line on the 74LS273 latches near it on red square, probably this should be the culprit for the jailbars. So i go on and i looked at the solder side for connections to and from the suspicious latch chip with the stucked line:
These are clear signs of oxidation and/or corrosion, a closer look after the cleaning reveals a broken trace under the dirt.
You can see other damaged tracks on the left but they are in working order. There is not enough room to apply a safe and robust patch in place so i had to use a small wire.
It’s time to test the board again … i powered it up and …
Yeah! No more jailbars and the board is fixed! Another case closed!
… and now … “Go forth brave adventurers and may the gods guide you!” 🙂
UPDATE: looking at the board i found a damaged volume pot in working order but hard to adjust due to its conditions:
Probably someone has been used a screw gun against it in the past to pump up the volume! 🙂
I removed it …
and i replaced it with a brand new one!