Well, when you get a RAM error on a Williams PCB, one of two things is generally wrong (but it could be worse).
1. You have a bad power supply and the RAM chips are not getting +5V. This is pretty common, however, in this case, it's not an issue because I have a Switching Power supply in the game.
2. The RAM chip is acutaly bad.
The easiest way to make sure that it actually IS a bad RAM chip and not something like a bad power supply, defective socket, or something else is to swap the RAM chip with the one next to it.
If you look at the picture, you'll see that the RAM is in the upper right of the board (if the batteries are in the lower right). There are three rows of 8 chips. If you look at the ROM board, you should see the LED flash 3 numbers. In my case it flashed a 1 - 2 - 5.
The first number indicates the type of problem the board is having. In my case the 1 means a RAM error. The numbers following that indicate additional information. In the case of RAM errors, it indicates ROW number then CHIP number. So as you can see, it thinks I have a bad RAM chip in ROW 2, Chip #5.
So what I did, is I powered the game down and swapped Chip #5 with Chip #6 in Row 2. Then powered the game up. If the chip is really bad, the error code will follow the chip. In this case it did. The LED now read 1-2-6. Now just to make sure, I swapped #6 with #8. Sure enough, the LED then read 1-2-8.
I replaced the chip (4116 RAM) with a good one and the LED read 0, which means it didn't detect any errors.