The owner was having different issues with both of these games. F-14 was registering an “Adjustment Failure” and Comet was missing all displays.
The “Adjustment Failure” and reset of factory settings on System 11 games is its way of telling you that the game is not getting power to the U25 RAM chip when the game is off and, thus, not able to retain settings, high scores, etc.
Most pinball machines get power to the RAM through three AA batteries that are, more often than not, mounted on the CPU board. Because most batteries people put in their games are alkaline based, over time, these can burst and cause corrosion damage on a CPU, which is a nasty mess and can be a real pain to deal with depending on the level of damage caused. That is why it is always important to regularly replace the AA batteries in your game! A good rule of thumb, is to replace once a year, or put in a memory capacitor or lithium batteries that don’t leak or burst over time.
The power runs from the batteries to 1N4148 diode at D2 and then on to the U25 RAM on System 11 Williams games. Sometimes the “Adjustment Failure” reading can be as easy as just replacing the batteries, sometimes a bad diode at D2, or a bad U25 RAM chip. Sometimes, however, it’s loss of continuity between components or a bad battery holder. For this F-14, the battery holder was the culprit. It was pretty brittle and beginning to actually fall apart.
I had pre-made a remote battery back, as it’s a good idea to get the batteries off the board. Whenever, I encounter a RAM issue on any game, if it still has the batteries on the board, I will relocate them. So, I snipped the old battery holder and soldered on the wires to my remote back and stuck it on the inside of the head away from the boards. I tested for ~4.5 volts on pin 24 of the RAM chip and we were good to go.
Once the “Adjustment Failure” issue was resolved, I set the game back to free play and tested it out. I noticed the top right flipper was having a lot of issues. Under the playfield, I checked it out, and saw the coil stop was very mangled, as well as the plastic on the coil. I ended up doing pretty much a full rebuild on this flipper with new coil, coil stop, screws, link/pawl and spring. That finished out F-14!
On Comet, none of the displays were working. On these System 9 games, the display power
comes off the power supply as -100, +100, ground and +5 volts. In this instance, the board was missing +100 vDC. Several issues can cause the loss of the +100 volts, but in this case it was the most common — an open 39k ohm resistor at R1. I replaced this resistor with a 39k ohm 2 watt resistor I had, put the board back in, and all displays were back up and running.
Once play-tested a bit, we saw a few adjustments and broken rubbers that needed replacement, but it was pretty much all the way back up to speed after the display issue was resolved.
The owner also had a 1984 Data East Karate Champ that he couldn’t get the second player controls to work on. I usually don’t do much work on arcade games, though I have done a decent amount of cap kits on monitors. I told him I’d take a look at it, and luckily, we were able to get everything up to speed on it for two player with some simple adjustments of the DIP switches on the CPU board.