Have you done a switch test? Maybe it's not detecting when they're down.

When you knock down the drops they are supposed to stay down until you hit the troll or the loop behind them.

But they should reset at the start of each ball too.

I'm no expert, but I filmed this when I cleaned my BG drop target assemblies. Maybe it'll be of some assistance for you.

Okay assuming you checked all the connections on both, I don't think it's likely that all the optos went out at the same time, maybe it's something with the switch matrix. According to the manual all the drop targets are on the same column. Two other switches are as well that you can test to see if they're still working, the left and right return switches, that will confirm if this problem is a problem with the column.

Okay that makes it a bit more tricky if the whole column isn't out. How about a manual test of the switch matrix, just to be sure, though. Remove the connectors 1J8 and 1J10, then if you short 1J8-3 & 1J10-7 it should register as the bottom drop target on the left side. Also have you tried reseating cables on the the interconnect board?

Untitled (resized).jpg

If there's room you can get an alligator clip cable on both sides and just short the pins together. To be exactly like the circuit is normally you can also get a 1N4004(or any non-zener diode should work, but that's the one used on a couple of switches I know like the cannons) diode to put in between em like in this diagram.

Untitled3 (resized).png

Okay, you're probably getting the adjustment error because those switches haven't been activated in a certain number of games. If they're registering fine on the board then we can at least rule that out. Back to the playfield, your connectors might be bad. If you have a meter you should test for continuity on the connections for the left and right drop targets, especially with the green-orange wire on both of em. If that wire isn't making a good connection then it would cause the all the associated switches to not register.

So when they are knocked down, all three, if you hit the stand up behind them nothing happens?

What about if you hit the bonus advance loop? Does the bonus advance loop light up after all three are down?

Huh, now this is getting confusing. You've checked the MPU, the interconnect board, and the connectors and none of them seem to be causing it.

On the drop target behavior, on my machine, running ROM L-8, the drop targets reset at the beginning of each ball regardless of whether or not they've been knocked down. What ROM are you running? The problem could potentially be a case of bit-rot and your ROM has become slightly corrupted.

I had a similar issue on both my Space Station and Taxi which, I believe, use the same opto board. The problem was that the boards simply weren't getting power. The supply is a separate connector J2 that gets loose because there are only two pins holding it together. If the board doesn't get power then none of the drops will register.

Looks like you have the L-A ROM installed. I had the L-A rom installed in mine but recently swapped it over to L-8, but forgot if the the drop targets reset each time. Just loaded the L-A version up in Visual Pinball and looks like with this software the drop targets only reset if they've been knocked down.

L-A had a few changes that I think were intended to make Big Guns last longer on route/make the game easier, I switched mine back to L-8 cause in the L-A version of the game the locked balls don't drain at the end of each game and locks are preserved from game to game.

Back to the power issue, here's the schematic from the manual. The board should be getting +12V.

20190217_143756 (resized).jpg