Per "the guide," If your batteries are good:

Step 1:
Is power getting to the U8 RAM chip?
With your game off and batteries installed, put your DDM on DC volts and put the black lead on the backbox ground strap. Then put the red lead on diode D2 on the CPU board. The banded side of the diode should show about .5 volts less than the non-banded side (which should be about 4.3 volts). If only one side of the diode shows voltage, this 1N4148 diode is bad.

Step 2:
test for voltage at the CPU U8 RAM chip. With the game off, you should get about 4.3 volts DC at pins 26, 27 or 28 of chip U8. If you don't, the battery voltage is not getting to the U8 RAM chip, and the game will boot up with the "Factory Settings Restored" error. Note pin 28 of the 28 pin U8 chip is in the same position as pin 1 of the chip, but on the opposite row of pins. Pin 1 is designated with an impressed "dot" right on the top of the chip.

If those check, U8 could have gone bad. If your batteries are good but you aren't getting voltage it's either a cold solder joint at the holder, or something bad in the holder.

_{Post edited by jalpert}

I wish I could take credit for the verbiage, but it was a copy and paste from "the guide." Years ago we used to have a document that answered about 92% of all the tech questions answered on pinside. The guide got taken offline, and has been largely forgotten about.

http://pinwiki.com has a lot of really good info, but this section in particular isn't worded nearly as clearly or concisely as "the guide."