Thanks for all of the suggestions! I will tackle these one by one...
Quoted from barakandl:There is no real simple and thorough DMM test for SCRs. You need to test them under load, do so in a real game.
Make a simple test lamp. All bally fixers need one. Take a lamp socket. Connect one end to feature lamp bus (6vdc)with a gator clip. The other end of the lamp socket place a bit of wire with a .100" molex connector.
Place the game in lamp test. Plug the test lamp connector onto the offending lamp driver connector pin and check there. If it never lights or is stuck on always, probably the SCR. Of course check the connector solder joint for never lighting lamps too.
I have a rig with SCR chart where I can test all the lamps really quickly.
This is a good idea; I will buy a spare socket and build a test lamp!
Quoted from Quench:Presume those lamps don't light up in the lamp test of service mode? and the lamps themselves test good in other sockets?
All switched lamps have common 5.4v power going to them on the frame connection of the socket, the corresponding SCRs for each lamp connects ground to the tip connection of the lamps. So to test the lamp socket manually, you need to jumper a wire to the tip spring part of the lamp socket to ground.
You could have bad solder joints on the male connectors of the lamp board that go to the playfield.
The 6K bonus left inlane SCR is Q17 on the lamp board. This SCR has a metal tab. Connect a wire from the metal tab to ground. Does this lamp light? Do the same on SCR Q10, this is the Drop Target 4 lamp. This will test the circuit from the SCR to the lamp.
Q23 is the Match light, you could use it to swap Q10 or Q17 as a test.
Go through the lamp/SCR section of the pinwiki for troubleshooting issues:
http://pinwiki.com/wiki/index.php?title=Bally/Stern#Failed_Lamp_SCRs
Correct, they do not light in test mode and the lamps themselves are good.
I made a bit of progress tonight, but there was a weird development. Now, a different set of lamps are not working:
- 1000 , centre lamp bank
- 1000, right spinner
- Drop target 5
- Purple standup target (this is what I referred to as the special target above - was referring to the wrong target!)
- 2x bonus
So, I set about testing them. I jumpered the spring pins of each socket to ground. Then I grounded the SCR manually. Some SCRs I could not test because they did not have metal tabs. If there is a way to safely ground smaller SCRs then please let me know.
- 1000, centre lamp bank (lit with grounded socket; could not test SCR)
- 2x bonus (lit with grounded socket and grounded SCR)
- 1000, right spinner (lit with grounded socket; could not test SCR)
- Drop target 5 (lit with grounded socket; could not test SCR)
- Purple standup target (negative on both tests)
So, I guess I have two more questions:
- Why do these lamps work when I ground them manually but not in game or test?
- Why does the purple standup target not light all (bulb verified to be OK)?
Thanks for any further advice 
