Now that the water damage had been repaired, I could finally rotate the game onto its bottom. I got a few friends, and we carefully righted the mammoth without incident. "Uneventful--just like you want it", my friend says. So with my friends still standing around, I quickly installed the power chassis, filled it full of fuses, and clicked out the interconnect for the first time. I was greeted with... nothing. No sound, no fluorescents, no flyback whine, no neck glow. Talk about anti-climactic.
I wasn't able to work on it for a few days, and during that time I realized that I had not checked the two fuses under the twist-caps. Sure enough, one was missing. With that fuse replaced, I powered up the game again, and this time I was surprised by a VERY LOUD BUZZ and not much else. Upon further inspection, my +5V was around 2V, and the +12V didn't look too good either.
Now it's time for my MCR donor to lend a hand. I pulled the power chassis and linear supply board from my Spy Hunter and installed them. It boots! It's alive! But no sound, no relay-controlled fluorescents, and no chase lights.
The sound, relays, and light sequencer all work from the 12V regulated supply. This checked really low, but I was running a known-good power supply. I chased it down to a short on the SSIO, then unsoldered components one-at-a-time until I found this one in a dead short:
How many components did I need to unsolder before I got to the cap? Well...
I replaced the cap with one from another board, and now the flashing fluorescents all work (that's good), and the chase sequencer and lights all work (that's very good)!
Now it was time to work on the power. The power chassis just needed new fuses and caps (the two giants). The linear supply board regulated properly without load, but dropped off immediately when hooked to the boards. I suspected the big transistors, so I shotgunned Q103 and Q104 from an old Bob Roberts rebuild kit I had, and got lucky. I'm guessing the missing +5V was the terminal condition of the game 24 years ago, so one of these two scoundrels was responsible:
With the game running under its own power, I could address the VERY LOUD BUZZ. I really thought is was a bad ballast somewhere, and I'm not exaggerating when I say that EDOT has a LOT of ballasts to unhook. Unfortunately, that wasn't it. Nor the ground straps. Nor the CRT. Nor the big caps (already replaced).
It turned out to be the these tantalum caps on the amp boards.
I missed it early, because I swapped the two boards and the condition remained. Turns out, BOTH boards were bad. Crazy.
So now, everything works! I have new sideart and vinyl from Rich ready to apply, I need to make a new back door, I need a new CPO, and a hundred other things. But last weekend, for the first time in 24 years, EDOT #241 entertained a small crowd!