This comes from Flipperwinlke:

Assuming the game powers on, you can test a non-working lamp's SCR's to see if it's working (this assumes you have checked the bulb, the lamp socket, and the wiring to the lamp socket).
While the game is on and in "attract" mode, press the Self-Test button inside the coin door ONCE. This should put the game into the "Flash All Feature Lamps" test (check your game manual if it does not).
Note which feature lamps are NOT working. Write them down. You will need this information if several lamps that connect to the same decoder don't work. A decoder has likely failed if 4, 8 or 12 lamps (multiples of 4) are not working.
Check the manual's schematics to figure out which SCR controls the lamp(s) in question. This information is on the Lamp Driver schematic page.
Look at the connectors at the right of the schematic. There the lamp name/descriptions will be listed.
Follow this line back to the first "Q" (SCR) that intersects this line. Note the SCR number (for example, "Q8"). If the schematic lists a "**" next to the SCR, this means it's a MCR106-1. Otherwise it's a 2N5060. Also note the chip that drives this SCR ("U1"). Both these components could be damaged (but generally it's just the SCR).
Write down the "Q" number and the lamp name on some paper. Also write down the driving decoder "U" chip number.
If 4, 8 or 12 lamps that all connect to a single decoder don't work, suspect the decoder "U" chip as faulty.
Press the game's test switch again to take the game out of lamp test mode. The display test will probaby come up. Leave the game here, as all the playfield lamps should now be turned off.
Connect an alligator test lead wire to ground. The bare braided wire in the bottom of the back box works well for this.
Touch the other end of the test lead to the ANODE of the SCR in question. On the large SCR, the metal tab is the anode. On the smaller SCR, it's the lower right leg. To make sure, the pinout for the small SCR's is silk screened on the board for a few selected SCR's. You are looking for the lead marked "A".
If the lamp does NOT light when the anode is grounded, the problem is NOT on the lamp driver board. Most likely you have a wiring problem, a bad lamp socket, or a bad bulb.
If the lamp DOES light when the anode is grounded, the problem probably lies with the SCR. Replace it and see if that fixes the problem. If not, suspect the "U" decoder chip that drives that lamp

Link to the page I found this on:

http://techniek.flipperwinkel.nl/ballyss/rep/index3.htm#driver

Hope that helps Tim