That's about the only difference - TP1 and TP2 are reversed between Bally and Stern Lamp Driver Boards.
Bally has TP2 as GND and TP1 as +5 volts DC.
Stern has TP1 as GND and TP2 as +5 volts DC.

TP3 on both mfg boards is a test voltage used for manually switching on SCRs for diagnosis.

If the respective lamp lights when you connect the lamp driver board test point TP3 to the gate leg of the SCR, then the SCR is likely good. When you grounded the metal tab of the SCR and the lamp didn't light, it was more likely a bad connection with your jumper lead - it should have worked seeing as TP3 to the gate leg worked.

Which lamp driver board and SCR(s) are you concentrating on at the moment?

According to the lamp schematics with reference to the two red-green wires:
Lamp board Connector J1 pin 3 (red-green) wire goes to the left spinner white lamp.
Lamp board Connector J3 pin 3 (red-green) wire goes to drop target #1 lamp.

Note with the lamp driver board, the connectors start with pin 1 at the bottom and count upwards - the other boards in the game start with pin 1 at the top and count downwards.

SCR_MCR106 (resized).jpg
2N5060a.jpg

There's three versions of LDA100 lamp boards. Rev A (blue colored) and rev B and C (green and skin colored respectively). Rev A has the SCRs layed out in different orientation compared to rev B and rev C.

Stern Rev A:
* small 2N5060 SCRs;
---- Cathode = bottom left
---- Gate = top
---- Anode = bottom right

* larger MCR106 SCRs;
---- Cathode = top
---- Gate = bottom
---- Anode = middle

=====================

Stern rev B and rev C:
* small 2N5060 SCRs;
---- Cathode = bottom
---- Gate = middle
---- Anode = top

* larger MCR106 SCRs;
---- Cathode = bottom
---- Gate = top
---- Anode = middle

Yep, SCR Q60 goes to J3 pin 3 according to the schematics. It's one of the smaller 2N5060 SCRs.

This should not work at Q60 on a rev A board.

Please post a picture of the lamp board and the SCR in question.

The letter "A" under "LDA" on the label says it's a rev A board.

When you ground the bottom right leg of SCR Q60, the lamp should light. All this will tell you is that there's connectivity from Q60 to the lamp socket.
When you connect TP3 on the lamp driver board to the top leg of SCR Q60 the lamp should light. This manually activates the SCR and tells you whether Q60 is working or not.

What about running a jumper wire from ground to the bottom right leg of Q60?
If the lamp lights, then yes Q60 is suspect.
If it doesn't light then there's a connectivity issue from the bottom right leg of Q60 to the lamp itself, or there's an issue with the lamp/socket.

Thanks for following up and great to hear it's resolved! You might get dangerous with that new desoldering station