hey steve,

i'm not near my DM now (in different town). you can dowload the manual for free here;

http://www.ipdb.org/search.pl?any=demolition+man&searchtype=quick

i'd check your ball trough. make sure it's not pitted by balls first (common with 90's williams pins). if so you can buy a 'sleeve' to put in it/and or get some emery cloth to smooth out the grooves. it sounds like an opto error, probably need to take a qtip to clean, or adjust, or replace the transmitter and/or receiver. hope this helps, i had a similar problems with my DH.

Likely an opto on your trough board, start with a good cleaning and then test the optos in the test mode by running something thin through the trough to see if they are all registering (should go in order). If #3 is not registering after cleaning it will likely need to be replaced, this can be done either by removing the old opto and resoldering on a new one, or by purchasing new ball trough boards (much more expensive)