This is a continuation of the post I wrote last night in case you couldn’t figure that out by the “Part II” in the title. (DUH!)
I removed the old rechargeable NiCad battery from my MPU board and cleaned up all the damage it caused. The battery is not really needed. It’s there to maintain high scores, settings, and book keeping info. I figure high scores and settings are important enough to warrant putting in a replacement for the battery.
Someone had already done something similar (but different!) on my Defender. I’m guessing they followed this tutorial by Bob Roberts. For that, they put a shiny round lithium battery in as a replacement…similar to a watch battery but bigger. I was thinking maybe that would be the route to go for this, so I searched the RGP and RGVAC news groups for more info.
I figured that maybe a lithium battery would be the best bet because they last so long. The alternative is to setup a remote mounted (3) AA battery pack. Bob Roberts has a tutorial for this as well (because he rocks). No matter which way you do this, if you put in replacement battery(s), a blocking diode needs to be put in-line before the battery pack to keep the MPU board from sending voltage to the batteries to try to recharge them.
On some posts in those aforementioned newsgroups (50 cents please), they mention that lithium batteries can be dangerous when hooked up improperly and can start fires. I’m not sure about this, but I figure that if I did put a lithium battery in and the blocking diode crapped out, my Baby Pac-Man might end up a big smoldering pile of ashes. Because of this (and because so many people seemed against lithiums for these boards) I ruled this option out. I don’t need any visits from Smokey the Bear, thank you very much.
There is also another option that I read about, where you can use a special capacitor that will hold the charge similar to a battery. With that method, you have to make sure to power the game on at least once every 6 months (I think). This sounds pretty cool, but I figured I would just go with the AA battery option following Bob’s tutorial. I ordered some diodes from him and a battery holder for $1.00, along with more lamps for the playfield. Here’s what I got:
Before I did anything, I ate the moon pies. Then, with my sugar buzz going strong I hooked up the battery pack per his instructions.
He mentioned putting a connector in-line so you could remove the board without having to remove the batteries. I thought that was a good idea, so I used some of these from Rat Shack:
I crimped them using my HT-1921 crimper that I got from Bob awhile back. He’s got a tutorial on crimping here.
I wrote the polarity for each battery with a sharpie, and added some zip ties in a couple places so if the wires get pulled, they don’t put any pressure on the solder joints.
One other thing I did a little differently – I didn’t use wires to connect the batteries. I’m talking about the 2 small wires seen here in Bob’s pic:
Instead, I turned the terminals down…
…and soldered them together:
If you do this, just be careful none of your solder drips down and touches the metal housing because it does conduct.
Here’s the other end connected to the board:
I ran my wire around the back, through that middle hole, and tied it off again through itself so pulling on the cable won’t pull on the solder points.
The last thing I did after hooking the batteries up was a test that I think I read about on Pinrepair.com. The whole purpose of the batteries is to keep a 5v (ish) charge on the RAM chip in socket U8 when the game is powered off. To make sure it was doing what it’s supposed to do, you can check the voltage on that chip with a meter by putting the red lead on the power pin of the chip (pin #22), and then ground the black lead. Here’s that test, showing it’s doing it’s thing.
Stay tuned for the exciting conclusion….