OP

Quoted from rlbohon3:

I bought a Firepower recently that is physically in great shape but will not boot up. IDK the history of this particular game because I bought it at an auction, but I believe it was home use only, likely very little use, no battery corrosion, no playfield wear, etc. Aside from needing new rubbers, lights and a polish/waxing of the playfield, it "looks" just about mint. However, powering it up results in the GI lights coming on and the two LEDs on the MPU light up solid. Nothing on the displays. It doesn't appear to boot. I also found that the ball ramp thrower solenoid was burned up.
Here is what I've tried so far based on @vid1900 's helpful bulletproofing tips, my own exploring and advice from others:
1) Replaced 40 pin headers on MPU and 40 pin socket on driver board w/ parts from Great Plains Electronics.
2) Replaced all Scanbe sockets for the 6 game ROMs (IC26, IC22, IC21, IC20, IC17, IC14) and CPU socket (IC1) with SIP sockets. I haven't replaced the Scanbe socket on the RAM IC13 yet because I ran out of SIPs. More on order.
3) Tested all pins in #1 and #2 above for continuity and shorts (solder bridges w/ adjacent pins); found no issues.
4) Found shorted power transistor (Q29) driving the burnt up ramp thrower solenoid. Replaced w/ new TIP120. Also replaced solenoid/diode. Fuse F2 for solenoids on the power supply would blow prior to fixing this every time game was turned on. Now not blowing after replacing transistor & solenoid/diode.
5) Replaced all 4 axial caps on power supply. 5V, ground and ~12V measured at 3J6 on power supply.
6) Reflowed all connectors on MPU, driver board and power supply.
7) Removed battery holder and wired in external battery holder.
8) Added fuse mod for lamp and solenoid rectifiers for safety.
No change in behavior. Turning on game results in GI lights coming on, two LEDs on MPU coming on solid and that's it. Nothing on the display. If I hit the test button on the sound board, it goes through all the sounds; that seems to indicate the sound system is working but doesn't tell me why the game doesn't boot.
So I'm not sure what to do next. I'm not sure what to test/diagnose, or what would be the next likely cause of failure. I did notice that when I had the game ROMs out, many of the pins looked blued and tarnished possibly due to heat. Maybe a ROM is dead? I am wondering if it makes sense to remove the 4 game ROMs (IC26, IC22, IC21, IC14) and replace with a combo ROM on IC14 from someplace such as Action Pinball. Also IC20 and IC17 flipper ROMs, maybe replace them too.
Also, would it make any sense to swap out the 6808 CPU (IC1) and the 6810 RAM (IC13) since they were socketed chips and easy to replace? Replacing the ROMs and RAMs isn't too terribly expensive, but then again I may just be throwing parts at it w/o knowing for sure there is a failure. On the other hand, with the other things I've addressed to this point, I'm looking for the next likely candidate. Any advice?
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