Have you checked the mech that lifts your targets... Had a bad lifter plate on my game

how are you drop springs mounted?
can you post a pic of the mechanizem?

Typical problem on Stern drop mechs. The mech seems to work fine when you manually push up the bar. But the solenoid pulls the plunger, not pushes it. The linkages got worn down over the years so there is some slop. Also, the reset bar may be bent down some. The result is the solenoid cannot pull the targets up enough to lock. I have not found a replacement link for these yet.
I superglued a zip tie on top of the reset bar to make up for the slack. It adds that 1\16" to 1/8" needed to push the targets up higher to lock. There are probably other options but this was quick, cheap and works so far.

Without a pic (and even then- may be hard to say why) its impossible to say. However- your best bet is to get in there and use your hands and fingers to trigger the reset and drop them and do this a number of times and basically just watch stuff move and feel how much force it is requiring. You could have a gummed up mech that’s simply not fully traveling- it could be a bent piece- it could be mid adjusted for height. All I can really tell you is that for just 4 targets the reset should be pretty easy and smooth. If your feeling much resistance at all it probably should be cleaned and then adjusted after you reassemble.

All of what the others said, for sure.

It is kind of hard to tell from the pictures but maybe your drop target cage assemblies are mis-located. I have had to relocate several parts on my different Sterns to learn and understand that these machine were not built using standards of high quality and close tolerances. There is/was a lot of sloppy manufacturing.

That said, It is difficult to tell from your pictures, but it looks like the fronts of the targets are riding, or contacting, the play field surface. There should be a gap, at least a little bit of gap between the targets and the edge of the cutout. If there is no gap and the targets are riding then there is possibility they are not resetting properly.

It is a long shot, but as I said, in your pics, it looks like the targets are riding the edge of the cutout. If that turns out to be the situation then you will need to relocate your drop targets assemblies 1/16" or so.

You have deep impressions on the lift bar that are preventing the targets from being pushed as high as they should.

You can glue a small hacksaw blade across them to nullify the groves, or try something else like the zip tie trick.

do you have 2 sets of holes for the bottom of the springs, looks kind of close to the base of the target?
the spring is what help's pull the top of the target onto the ledge, that hold up the targets.
Also make sure there's nothing down on the ledge that might not let the targets set.

It is a long shot, but as I said, in your pics, it looks like the targets are riding the edge of the cutout. If that turns out to be the situation then you will need to relocate your drop targets assemblies 1/16" or so.

agree' looks to close to the wood.

Easiest is to remove the drop target assemblies and sort "bench test" them. remove the two screws for the coil stop and remove the coil. Instead of letting the coil hand and add stress to the wire, I like to tie wrap the coil to something that will support the coil's weight.

4 screws and you will have the drop assembly in your hand. See how those targets operate and lock while on the bench.

Take a movie of the action, and then many smartphones let you (edit) and re-save with "slow the action down to .5x" -- this really helps you see what is going on.

tip: put resolution on 480x640 to keep the file size down if you are emailing it to a friend vs youtube.

1. is the drop going high enough?
2. is the drop going too high and bouncing off something

etc...

mof

Ooh. Hacksaw blade. Probably better as eventually the zip tie will get cut by the drop target blades.

i have found that many of the replacement drop targets are warped/curved which causes them not to be secured in the up position or bowed to the point of contacting the playfield when in the up position, since you have several sets use only the straightest of them - you can try to straighten bowed drop targets by heating them in boiling water and bending them back straight, new springs are a must and like others have mentioned install drop target mechanism pushed towards the back of the playfield to maximize the distance between the target & playfield

i wouldn't start drilling holes to move the whole drop assembly tho

Is it possible to know the outcome of this situation? It is now 2021, and I am having the same problem on my Stars.

i believe it is best explained in #6 that the target faces are touching the playfield.

the target upon reset needs to move/be pulled forward by the spring to allow the target to rest on the bracket.

imo, the target assemblies in the first pic need to be moved rearwards a little.

also the original drop targets did not have the ledge on top.
i understand the ledge being introduced/made for inline drop targets but not side by side.
so the situation may arise where as the drop target is being lifted and the new 'ridge' hits the post rubber behind making it difficult to correctly set up the drop target bank, and vice versa once reset and the target is hit by the ball, the target is ever so quickly pushed back and this new 'ledge' hits the post rubber behind 'bouncing' the target forward preventing the target from dropping.

the problem with reproduction parts is sooooo many just aren't made to spec/as per original.

Well, the OP put up this post and disappeared with no resolution.

Can you up put up some pics of your drop targets?