Can you possibly see both sets of optos illuminating underneath the ship?

Mine has done that a couple times recently. I figured it was just dirt or something has fallen in front of the opto for the drop. Doesn't do it every time.

It's definitely a flaky opto. Put it in switch test. There's probably some dust in front of the opto

Unplug the optos and plug them back in. See if that clears things up.

LTG : )™

Have you put washers behind the ledge that holds the drop target up. This is a common issue that can be fixed with washers. There is a thread about the drop target not staying up that I can find for you later if you can't locate it.

It's optos

not sure if same problem your having but mine would pick a mission as soon as i hit start, it would fire ball off, the drop target would go up and down several times and start a vengeance mode. The washers under drop target fixed mine. heres a video i made fixing mine, maybe it will help yours.

Hi again,
My ST Pro's left front opto had a bad solder under the ship and directly behind the drop target. I re-soldered it. The left opto is a transmitter and the right opto is the receiver. Lift the PF look for the opto board to the left of the ship. The led illuminates when the opto is working properly genteelly wiggle the wires for the opto and see if the board's led light flickers, goes out, etc.???

Not necessarily. The same exact problem can occur from the drop target not catching the ledge. It is very common and washers will fix it.

Bump
Would like to know what you find that fixes it.

You need washers behind the drop target ledge it fixed mine

This problem has been documented before and happens a lot. The drop target is not catching the lip of the plastic that holds it up or it is broken. Installing washers underneath will fix the problem. If it is broken, PBL sells the part for a few bucks.

https://pinside.com/pinball/forum/topic/star-trek-le-drop-target-wont-stay-up#post-2073538

Washer fixed worked for me when mine did that.

The washers worked for just a short time. I used 1/32 and 1/16....even replaced the ledge that broke after putting in the washers. Tweaked that darn thing for weeks. So what I eventually did, that has now lasted for 2 months is the same fix that was recommended on the drop target on woz.
With the pf in upright position, grab the whole drop target assembly and push it towards the front of the pf. It's very hard to bend it, so just bending it a slight amount has kept the drop target from not setting on the ledge. Worked on my woz and now has worked on my st.

My plastic is broken as well, but it still functions for the moment so I haven't replaced it. I think it can't take the force from the drop target when it is held up by the washers for long. (Kind of like a karate master chopping boards held up by two cinder blocks.) I have an idea to put a small strip of felt tape or something behind it when I next replace it to see if that evens out the force and makes it last longer. Not sure if that will work or if I have the right thickness tape. Still, it might be something you want to try when you replace your ledge.

For those with a 3-D printer, you can make your own stronger replacement. Follow this ink for the downloadable pattern file.
https://www.thingiverse.com/thing:969909 sterndrop-3_preview_featured.jpg