On the main pcb, the eproms will be in sockets and normally have a sticker on them. All chips (Eproms and others) in sockets can be re-seated to see if this will fix the problem. To do this gently slide a flat blade screwdriver between the eprom and the socket and lift it up slightly.  Don't worry about pulling the chips right out, just lever them up 2-3mm and then push them back down. When you are levering the chips, make sure you keep the screwdriver blade parallel to the board otherwise you may damage the tracks located under the sockets.

The best place to measure the 5v is across a couple of the chips on the main pcb. If you can post a picture of the board, we might be able to suggest a suitable location.

regards Derek