Chips and Boards (mostly OK!)

 I have been debugging lots of problems in the machine. First, some good news, I've gotten the screen working. I've replaced it with a completely new one:

I have a few problems with it, but that'll be for another post. Tonight's post is about CPUS.

Have Iron, Will Travel

Part of debugging the screen has me questioning that the CPU board is in good shape. I'm pretty sure the power supply isn't helping (again, more later), but I decided to take the CPU board out, and see if I could see anything obviously wrong with it.

The CPU board was largely in good shape. You will note, there's a battery pack on it. This needs to be removed because, over time, the batteries leak, and put an alkaline all over the board. While this doesn't immediately ruin a board, over time it well. So, that's coming off:

Otherwise, as I inspected the board, I didn't see any obvious problems. The capacitors all looked good, the chips all looked good, the transistors all tested well, but I did notice someone had been here before me fixing a driver transistor:

Testing of all connections, it looks okay to me. I do see a little off-coloring on the board. I'm not sure what that is:

But, so, I reflowed all the connectors, and while I didn't notice any cold joints, it's still good to do.

Similarly, I touched up the top of the connectors with a bit of sandpaper.

And while doing that, I noticed something fishy. Do you see it in the above photo? Look at the top left of the connector, it's missing a pin:

Well, that's not right. So, let's see if it's a problem. Checking the CPU schematic:

Uh-oh. It looks like pin 19 is important. It's sent to the sound board. I guess we should check the sound board, and see if it's important:

Oh, it looks like pin 19 isn't connected to anything. I could replace this connector, because this CPU board might someday be removed from my machine, but whoever does that will probably check the board carefully. Having typed that, I guess I should replace it anyway to help that dude out.

Otherwise, the board looks pretty good. No obvious problems except 4 missing cabinet screws – that'll be easy to fix. I'm waiting on the RAM replacement, and I might upgrade the ROMS (see the future articles about the screen).


  1. Pin 19 is always missing on these boards. That's standard.


Post a Comment

Popular posts from this blog

550-5038-01 (part 1)

Twinkle Twinkle Little Star