You now I'm not a tecchie at all so I'm probably going to ask stupid questions here, please be indulgent...
Here's my attempt to fix a TAITO Space Invaders "L" Shaped PCB with the tremendous help of my friend "4l4in" AKA the technigician.
He has the tools, the knowledge, the patience to explain me even the basics and he agreed to help me on this mission.
Thank you, thank you for that, buddy!
First of all, you have to know there are 2 similar boards involved.
Let's call them "
Oxford" and "
Lancaster" which are roughly the names of the places where I picked them up.
Also note that we doubled check the voltages and they are correct (+5,+12,-5V measured from the board).
Here's the log of where we are (stuck) at the moment.
Any help or suggestions are welcome.
Lancaster PCB:
When plugged is showing only 2 flashing dashes on the screen.
Checked with an oscilloscope, the processor and memories seem OK.
No sound.
When checking the original ROMs, they seem defectives.
So we swapped them with the eproms from the Oxford board.
Game starts, displays scores and targets, then offers to select either 1 or 2 players.
When I start the game, the game screens start to appear and then the game resets.
Credits are stuck on 40.
We decided to program a set of EPROMS to try it.
We programmed the set with the ROMs from MAME "invaders.zip".
Didn't work at all.
We then compared the original ROMs with what was available on the internet and found out that what we needed was the "Space Invaders (TV Version)" ROMset called sitv.zip
After a close check it appeared that our original ROMS had the exact same content as that set so the problem doesn't come from the ROMs.
"Fausse route" as we say
So, so far we still have our problem: game keeps on resetting after attract screen.
When launching the selftest mode, it stops at the RAMs.
Found on the net that the test mode displays which RAM is defective using a code from "1 to 8" and from "A to H".
Amongst the garbled screen we could see a letter G displayed in the middle of the screen.
We then replaced the 7th RAM.
Selftest is now OK.
Text now displays fine on the screen.
Unfortunately as soon as an invaders appears on the screen, game resets itself…
As long as it's only displaying text everything seems OK.
to be continued...Oxford PCB:
Doesn't start at all.
Found an IC defective that was preventing the synchonisation of the RAMS.
Replaced the IC.
Now we can launch the selftest procedure.
It says that RAMs are OK and you can hear various sounds.
The game is stuck at the first screen.
Graphics in test mode are OK but are garbled in game mode.
to be continued...
