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Hello,

I would really appreciate some help with restoring an old Defender Cabinet that has been in storage for 25+ years in a house without proper heating and isolation. I managed to grab this machine, Operation Wolf and a generic 1943 cabinet.

Picture included for those interested:

Defender.jpg


I am very new to this thing so bear with me. The old Linear PSU was toast, there was a small burn hole straight through it and components had been soldered together in such a way that I did not feel comfortable using it. It blew fuses left and right. So I changed it out for a PSU on Paradise Arcade Shop. Now the cabinet now powers on without issues. I also took out the CPU board and gave it a cleaning since it has clearly been a victim of battery acid at some point (Picture is from before doing the cleaning). After cleaning I did some probing using a multimeter on suspicious points to see if there was still contact between traces. I found nothing that really stuck out and the board seemed okay. The thing started and I could hear the iconic bootup sound, but the machine booted up to a blue screen with nothing seemingly happening except for a slight burst of "static" or "jumping" on the screen which to me indicated rebooting. It also seemed that the board could not complete initial ROM or RAM checks. The four LEDs lit up right as the cabinet started and turned off almost instantly, and then none of them ever lit up again.

So i started googling around which lead me to several threads here and I noticed how common it was for the 4116 RAM to fail. I tried turning the game on for a couple of minutes and noticed that all RAMs were cold with the exception of the rightmost RAM in the middle row which instead was really warm. I bought a full set of 24 RAM modules from this place: https://www.sintech-shop.de/en/4116...mtVvwz7C6aTXieFgrc0rEty8s2jn-FNRjEeO852w52m5A

Since I live in Europe it is really hard to come by certain parts here and this seemed to be the best option for me. I got the RAM home yesterday and started off by slotting them into the CPU board and I changed out the 40-PIN cabled between the ROM and CPU boards for good measure. Then I put the board back in a booted the game. The machine started (I wish I took pictures of the screen. The machine is not at my home at the moment. It's standing in a workshop about 15 minutes by car from my home) and I that the blue screen now only made up about a third of the screen with a slight diagonal offset, inside the blue parts I could see small artifacts moving a little along with small black dots. The other 2/3s of the screen was just dark. After about 30-45 seconds I noticed that the ROM board LEDs 1 and 4 were lit up. I looked it up online and first assumed it was complaining that ROM 9 was bad, but a few minutes later I also noticed that lights 1 and 4 being lit may also indicate RAM failure.

So I started taking out the new RAM one row at a time to see if there was any difference. The only thing I saw was the parts of the blue screen started having vertical black lines in it. I also checked the voltage to the RAM by measuring the corners. -5.10 volts, +4.99 and +11.99 which seems fine. So I put all the RAM back in but failed to noticed that I (like an idiot) put the rightmost top RAM in upside down. The RAM chips I bought were not really always clear which way they had to be put in since some has a really thin notch at the top and others had none at all. So I managed to fry one of my new RAM modules when I tried powering the game back on because I was not careful.

So, here I am turning to you. Do you have any pointers on where I should go from here? I am ordering more RAM today, going to have some more modules as spares. I am also aware of the 4164 RAM mod, but I want to try to get the machine in a working order before doing any potential modding.

Summary of things I have tried:

  • Changed the old Linear PSU with a Paradise Arcade Shop PSU
  • Changed the 40-PIN cable between the ROM and RAM board
  • Changed out all the RAM
  • Cleaned and sandpapered the legs on the ROM chips
  • Measured voltage to RAM
Is it possible that the CPU is bad? What about the chip directly under the 40-PIN cable. What is it for? I can't really seem to find any information on it except that it is a 7641 512x8 PROM from the schematics on https://www.robotron-2084.co.uk/hardware/boardset/williams-defender-early-series-boardset.

I have never used an oscilloscope or a ROM writer before and I am getting really lost here on what I should do next.
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