Here we go again... found this Chopper that's been sitting for at least 20 years.
Tearing into it, I was pleased at how relatively simple the game is.
Couldn't find much info, my serial is #344 and the few other ones I could find were all under 500 so guessing 500 were made.

Reading the pinrepair the downfall is that while it relies on a lot of common solid state components, some are discountinued/unobtanium.
Gameroomrepair.com has an EXCELLENT 4 part series on youtube going over the major aspects of the game and how everything functions -

Here's the main schematic: https://drive.google.com/file/d/1HL30R8ygmuofGh97RDPFAraTXuMeCSiz/view?usp=sharing
Logic schematic: https://drive.google.com/file/d/1Uh3fLVIDS54TyDoJxI0V94LuN4fInrsb/view?usp=sharing
Parts catalog: https://drive.google.com/file/d/1qohdY5_pIby0w6M6FhzyVD1r3IA6jAdt/view?usp=sharing

Good news:
It's complete!
On top of that, there's an extra display/logic board, an extra photo sensor board, and an entire extra target motor assembly.
Cabinet shows its age, but is solid and in relatively good shape
Glass is all clean with no scratches
Rear lithograph is there, some UV fading from the bulb at the top but overall excellent shape! I scanned it all for backups.
It fortunately comes apart in a few pieces allowing me to fit it into my otherwise small entrance basement!
I even found the perfect spot for it tucked under the stairs.

Bad news:
The logic board that boots, the displays are shot
The other logic board has good displays, the game doesn't start
Motor 2 isn't moving up or down, the TIPs diodes and transistors all test good, ordered the last cheap UA741HM driver on eBay
4/5 of the target sensors were testing out of spec
The 8 track deck is missing

So far I got the game mostly going, cleaned and adjusted some switches, replaced some large capacitors, the chopper works, 3/4 of the motors work.
I will be replacing the 8 track with an Arduino.
The logic board with the good displays will have to be repaired, in the meantime the one with bad displays is fine for testing.

The spare motor target unit has a good sensor so have been using that to test the photo sensor board.
Ordered some GL5528 photoresistors on eBay (10 for $5). That with a 200 ohm resistor in parallel creates enough resistance to trip the circuit!
While gameroomrepair.com has some NOS ones on his site for $22/unit, glad I was able to make something work for cheaper!

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I know the back scenery is often missing for people, I scanned and merged mine here.
It's 32.75"W and 25"H.

Really getting into it tonight trying to get the motors/hit detection working.

The wires that connect into the opto board are possibly internally frayed, or bad connection at the pin/edge.
The connector has some green oxidation so going to soak it in vinegar then rinse then dry.
Replaced the sensors on motors #1 and 3

Noticed on the schematics some spare A138 transistors being used in the (not needed) tilt circuit in case I need to harvest some for elsewhere.

Where the motor/worm gear makes contact with the gear is very touchy!
I was loosening the motor mount and dialing it in as it tried to move.
The screws that were on there were crap so replaced with #6-32x1/4" with a lock washer.
#2 the gear track in the shaft is 2 pieces that keeps separating, going to plastic glue it.

I was mounting the motors with one screw, need to make sure they're lined up with the hole in the playfield so they can trigger the EOS switches appropriately.
FYI each motor the wiring is the same, but the sensor board and mounting brackets are unique!

Spent $40 on an Atari pinball credit display to try swapping in new displays to the working board.
Still going to try to repair the other one eventually.

Tried to scan in the 3D sensor plastics. Very cool but didn't scan too well.

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Spent a bunch of time all over today!
Figured out the motors - I was concerned about the motor mounting hardware - a 1/4" lock nut screw with a washer at the top, a tiny 1/8" screw at the bottom with no washer. This was across all motors and I foolishly swapped out the hardware for new and modern stuff. Put the original hardware back in and now all of the motors move very smoothly!

Took a look at the bad logic board today (with the good displays). Cleaned up some previous work and burnt traces, touched up some of the vias. There were 5 wire "hacks" on there. Compared to the original board, not sure what the were doing with these. Pulled these off. The game now starts! It started after just a coin was put in so maybe some more work to do there. There is lots of evidence of lots of questionable work on this board. Lots of chips were replaced. Spent a good amount of time just buzzing out the traces.

I got an Atari credit display pretty cheap on eBay ($44 shipped) and popped it in the good logic board (with bad displays). On the Atari side, the display was socketed which was very nice. I tried to re-use the socket but was too difficult to fit in the Chopper board. The one I transferred looks perfect! The other display is dead and the power source looks good so need to look into that side next.

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Thanks but that's the unhacked board vs. the hacked up one

Spent some more time with the logic probe today. Traced the dead timer display to 2x bad DD700 display drivers. Got some equivalents (SN75480) on eBay for $11 shipped. The displays themselves look pretty good so I'm optimistic they'll look good after this!

Whenever I have the opto target hit PCB attached the program relay and hit relay lock on. For now I have it disconnected. I see I'll also have to revisit the resistors in parallel with the sensors to get a lower voltage. Once they hit the target PCB, there's a 10k ohm pots in series to each sensor to tweak sensitivity.
On a lighter note of that board - I cleaned up the connector and pushed the pins together a bit more and toned it out with my meter to ensure I'm getting good connectivity. Despite the game starting the light on the helicopter seems to come and go, may be related.

Lots has happened, I've been putting in random time over the past couple weeks.
Here's some highlights:

-Swapped in a display for a dead one and it worked great!
-Somebody needed the gears for the throttle assembly/pots so I measured them and created models for 3D printing
-Figured out the program/hit relay being locked on - the pots on the opto board were turned up too high. When I dial them clockwise (0 ohms) the coils release! This means that the opto board appears to be working. I need to analyze the circuit and see where my resistance needs to be where it isn't.
-The other opto board has some issues, I tested it and noted where it needs help

You too buddy!
It’s going ok, i need to get the sensors registering properly. Have a lot of other projects right now but hoping to get back to this soon

Little bit of progress, pulled the resistors and the chopper light is triggering the motors!
So let it be known the GL5528 is a drop-in replacement for the light sensors.
I did have to turn the pots all the way down.

Replaced the bulb with a white LED, much brighter! Drop in replacement also. I tried to remove the bulb from the socket and it was corroded on there. Pulled the bulb itself out of the bayonet housing, still could probably work if I wanted it.
Adjusted the motor at the front linkage and now also have a nice balance of forward/reverse power.
Went through and played a game!
The current main board isn't counting up time or scoring, so that's next to look at.

I have all of the plastics off now and messed around with 3D scanning them with an app on my phone.
Not bad for a quick rough run.
I like to make "backups" of whatever art I can but I suppose this will have to wait.

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Swapped in the other good display to the good PCB, now it totally works!
The other one needs to register hits and start counting so ordered some new chips.
Got the aliens mounted and the loose building, put back on the display shroud!
Pretty sure the sound board is toast.
I have some cheap amps I'm going to hook up.
Bench tested the setup.

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Dug through Atari manuals to find that the displays are Beckman SP-352 Panaplex displays.
Some are on eBay ebay.com link: S2T5 Beckman SP 352 Gas Discharge 2 Digits 7 segment Display

Was still having issues with the sensors, got it all squared away today.
Using the GL5528 sensors with a 1.8k ohm resistor in parallel was what worked for me.
From there you can dial in the sensitivity on the target board.
Tidied everything else up - tightened up the chopper body, put the backdrop back in, tucked all the wires in and tucked it back into its little corner!

This was a fun little project. Took a little longer than I hoped but I learned a good amount and would love to help if anyone else is trying to get theirs working.

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We moved into a new house so Chopper is next to some new friends.
Had an issue with one of the targets not hitting.
In the trigger circuit, I replaced 2 of the mylar capacitors and the transistor (2N3904 in replacement of the ancient A138).
After lots of troubleshooting I discovered that I was getting a flakey connection at the circuit board from the target sensor.
I cleaned up the contacts of the motor assembly connector and pushed the pins in more and she's working great again!
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I think I did like .08". The factory helicopter is thinner than that.