[BOREDOM DISCLAIMER]: I’m going to apologize in advance for what you are about to read. It is bound to be pretty boring. I’m going to go through everything I did to my Moon Patrol PCB last night in hopes it might help me fix it down the road. Buckle your seatbelt, cuz we’re going in….
This is a continuation of my Moon Patrol saga…if you don’t want to miss any of the exciting details, you may want to back up a few posts.
My mailman arrived yesterday. I was expecting him, and had let my dog out early for his arrival (j/k…I don’t have a dog). You know how The Postman Always Rings Twice? Well at our house, it’s more like The Postman Never Rings, Not Even Once. We have a shiny new giant door bell that is very noticable, but it goes untouched. This guy is a knocker.
Now don’t get me wrong. I like knockers just as much as the next guy, but when I’m working at home I like to have the music on. Because he likes to knock softly like an old lady with sore knuckles, I have to keep the music turned down low. This is also annoying because sometimes he comes around 12:30, but other times not until it starts getting dark out. Anyways, enough ranting about the mail…here’s what came:
What could this be I wonder? I flipped it over, and took a close look at the customs declaration.
Now I remember! These are those electronic pants I ordered from the pants district in Beijing! I hope they fit!
I ripped the package open with visions of my lower half plugged into a power outlet, and was incredibly dissapointed to find 16 of these:
I only ordered 15, so I guess one is for good luck.
Remember that boredom disclaimer up top? OK…if you are still reading, here is where I may loose you. I popped 2 of these in, to replace the suspect RAM. There are only 2 RAM in Moon Patrol as far as I know. Hooked it all up, and the problem was still there. So…according to the manual, problems can also occur with logic chips that are in the RAM circuits. The first one they mention is a 74LS139 chip in spot 2K on the main CPU board. I have a logic probe that I have never used. I figured it would be a good time to try it out. Everybody remembers their first time with a logic probe…do you remember yours?
So…I hooked it up and probed away like one of those aliens from the book Communion. I read the data sheet for this chip that I found via Google, and thought maybe it wasn’t doing what it should. In retrospect, I think I just don’t know what I’m doing. I ended up swapping out this chip with one I had on an old board and it did squat.
Now, because I am clueless, my options here are limited. I started looking over all boards very closely on both sides. I was looking for broken traces, or anything else that stood out. I noticed on the Character board (part #M-52-B-C for those taking notes), pins 9 & 10 on the chip at location 8B had solder connecting them together.
I thought that was a bit odd, and looked up this chip in the schematic. While I don’t understand much about the circuit, It definitely looks like these pins are not supposed to be connected. So, I desoldered them and put the board back in the cabinet. Now, the original problem was still there in addition to a new one. Everything that was supposed to be black on screen was now blue. I soldered the pins back together and it didn’t fix that.
I noticed a repair on the bottom of the Scrolling Video board, under where the ribbon cable connector goes. There was a gouge going right through 2 traces and someone repaired that with 2 blue wires. What is weird is that if you follow the traces they are replacing, it looks like they accidentally ran each wire to the opposite location. I desoldered them and soldered them where I thought they should go, like so:
The board is pretty much dead. I’ve decided that I messed with it enough, and am going to buy one that I know is working. When I get a bit better with this stuff I may take a crack at fixing this one.
Final Score: Moon Patrol 3, Jamie 0.