TP3 connects to TP1 via a brown-green loop wire at connector J3 on the solenoid driver board between pins 13 and 25. Sounds like you've got a bad connection on one of those pins meaning you have no power to the logic circuit controlling the solenoids.

SDB_LogicPowerA.jpg

Somebody's already reflowed that pin header - that's not factory soldering. Did you actually check the crimp terminals on both ends of that loop wire?

Q19 drives the coin lockout coil on the coin door, having it cut off won't affect anything and won't cause any game play issues.

If you've got a desoldering gun then you can give it a shot cleaning and resoldering those pins. My money's on the crimp terminals though - that's usually where the problem is.

BTW, what kind of multi-meter do you have? I'm curious why you're reading 97 volts on TP3. If you were getting zero volts there I'd be telling you to temporarily jumper a wire from TP1 to TP3 as a test to see if the solenoids start working. If that 97 volts is real and not phantom, I'd be concerned.

Have you worked out why you've lost connectivity over that brown-green wire at the Solenoid Driver Board (SDB) J3 connector yet?
TP3 on the SDB connects to TP1 via that J3 loop wire. TP1 is 5 volts DC power for the whole game. Without 5 volts reaching TP3, the logic circuit on the SDB controlling the solenoids has no power so all your solenoids will appear dead because the Q1 - Q19 driver transistors can't be activated.

That 97 volts you read at TP3 must be some phantom reading from your multi-meter because it's open circuit. It should read either 5 volts (presuming the connection over the brown-green wire is good) or zero volts if there's lost continuity over that brown-green wire connection. Confirm the TP3 voltage if you have access to a different multi-meter.

Just hook up a jumper wire between TP1 to TP3 on the solenoid driver board. Do the solenoids now work?

Cool, ok do us a favor and open a tech support thread in the early solid state tech sub-forum:
https://pinside.com/pinball/forum/forum/tech-early-80s-solid-state

The issues you're experiencing are just generic problems and not really specific to Space Invaders.
You can start the thread by copy'n'pasting or quoting parts of the below and respond to them:

Recrimp both ends of that brown-green wire with new terminals. Add redundancy to that circuit by performing the mod that ties TP1 to TP3. See the three bulletproofing mod posts #8, #9 and #10 for the SDB below which also includes ground mods for capacitors C23 and C26:

https://pinside.com/pinball/forum/topic/vids-guide-quick-bally-driver-board-repair-bulletproofing#post-592756

Don't worry about remeasuring TP3, you were obviously getting a bogus reading.

Solenoid 10 is the small coil on the coin door, solenoid 11 is the flipper enable relay on the SDB. 11 is working otherwise the flippers wouldn't work.

Switch test mode only reports the lowest switch number it finds closed. So you need to make sure all drop targets are in the raised position and you remove the ball from the game. The game should report "0" in the ball in play display. If it doesn't let us know.
Then with the manual in hand opened to the switch ID page, manually activate each switch starting from switch 40 and work your way backwards to switch 1. Report any switches not responding or switches that report the wrong number.

Download the Bally 1980 Parts Catalog from pinwiki:
https://www.pinwiki.com/wiki/index.php?title=Bally/Stern#Parts_Catalogs

It has part details of assemblies and should help.

It's 2 lots of 8 cables (16 individual lamp wires - 2 lamps share a wire). Refer to the Auxiliary Lamp Driver Board schematic. Note the blue wire in the door frame marked as ground should really be feature lamp 6.5VDC supply that's daisy chained to all lamps.

SpaceInvadersAuxLampBoard.jpg

When you say "emit a long tone", is it two alternating tones like an alarm? If yes, what you're describing is a slam tilt condition which causes the game to reset.

Then it could be a power/connector issue as vec-tor was getting at.

The transformer was upgraded to support a higher current load for a greater number of feature lamps (infinity lamps around the backglass).
The E-122-131 transformer was only used in Kiss, Space Invaders and Future Spa.
If you're going to use LEDs in the game that consume less current, you can get away with a common E-122-125 transformer.

@GKW, your opening post in the other thread says you have some 122-125 transformers already. Curious why you need the K's Arcade one? (which BTW says it's out of stock).
Space Invaders has the transformer and rectifier board in the cabinet unlike other games of that transformer/power type era.

See this image from the previous page in this thread:
https://images.pinside.com/9/90/dd/990ddbeff994702aac323a771161b1ee4e0c9f57.jpg
Ignore the aftermarket mod on the centre plank of wood.

A beefed up rectifier board doesn't remedy a lack of power; higher voltage and current capacity are a function of the transformer. And by beefed up, all it means is it has bridge rectifiers that are capable of running at higher currents and the PCB should have thicker copper traces. The standard Bally rectifier boards with E-121-125 transformers has a 10 amp bridge rectifier for the feature lamp circuitry. The Bally rectifier board for the E-121-131 transformer has a bridge rectifier setup capable of working up to 15 amps.

Most of the aftermarket rectifier boards these days have a 35 amp bridge rectifier for the feature lamps circuit.

The rectifier boards J1 playfield connector for Kiss, Space Invaders and Future Spa was increased from 8 pins to 9 pins. The 9th pin is a load sharing wire running to the playfield for the feature lamps so there's two feature lamp power connections at the rectifier board (reliefed connector/wire stress), not one like the earlier games.

On the main lower flippers, just stack the two switches together like this - note the second normally open switch is what switches on the upper mini flippers.
Also, the upper mini flippers have a secondary normally open switch but they're low current switches wired in the switch matrix and all they do is trigger a sound effect - no effect on game play.

SpaceInvaders_FlipperSwitches1.jpg

Heh, you replied while I was in the middle of editing my previous post to clarify the upper flipper switches.

The normally closed EOS switch is the same for the upper mini flippers, however the secondary normally open switch on the upper mini flippers are just low current (gold contact) switch matrix switches that have an isolation diode like all other playfield switches. All these do is trigger a sound effect.

The Bally parts catalog says:
Right upper flipper switch part number: ASW-A1-202
Left upper flipper switch part number: ASW-A1-203

Sorry, I don't have this machine but a picture of the right upper mini flipper switch mech was posted near the top of page 9:
https://pinside.com/pinball/forum/topic/bally-space-invaders-playfield-restoration/page/9#post-6009274

Switch "SW-1A-130" might also do the job.

Must be costing you a fortune getting them internationally - have you tried local?

The siren is produced by the same sound generator chip output as the background thumping sound. So their source is electrically the same. You'd have to learn how the sound generator chip is programmed and modify the sound ROM to reduce the sirens programmed volume level.
Otherwise you could try also running the speaker output to a sub-woofer that amplifies the low-end frequencies of the thumping sounds. This may not be precise.

Games of this era didn't have toppers. If you've seen one it's something aftermarket - have you checked CPRs website?

Use switch test mode to help tell you which switch the game is seeing as closed. Remove the ball from the outhole, make sure all drop targets are raised and go to switch test mode by tapping the little red test button inside the coin door five times. The player displays will show a number corresponding to a switch (Switch IDs are listed in the manual) that it's seeing as closed.
When the ball in play display shows '0' the game is not seeing any closed switches.

That pin/wire was originally designated for earlier games that had the knocker in the headbox. Your game has the knocker in the cabinet (it now gets power from J2) so that wire at J3-13 was no longer needed.

The physical connector is numbered with pin 1 on the very left and pin 9 on the very right. So:
Pin 1 - Gen. Ill. Return, (white)
Pin 2 - Gen. Ill. Return, (green)
Pin 3 - spare
Pin 4 - key
Pin 5 - Gen. Ill. Bus, (orange)
Pin 6 - Solenoid Bus, (brown)
Pin 7 - Switched Ill. Bus, (blue)
Pin 8 - Gen. Ill. Bus, (red)
Pin 9 - Switched Ill. Bus, (blue)

RectifierBoard_J1_Playfield_Connector9.png

Silverball Mania which came out before Space Invaders had the same horseshoe and centre target setup.
Bally released the following service bulletin for Silverball Mania to make the horseshoe a little tighter to enter:

SilverballMania_ServiceBulletin.jpg

The twist caps are not factory.

The 12 volt orange wire from the rectifier board that runs to the solenoid driver board at connector J3 pin 11 is converted to 5 volts that powers the logic boards. That connection at J3 pin 11 often burns and fails. So the hacks are running the orange wire directly onto the solenoid driver board bypassing the connector.
The other twist caps are probably bypassing other failed connections at that J3 connector.

IMG_0004a.jpg

Hmm,
The game I have here definitely doesn't have those twist cap mods.

If you're able to reprogram EPROMs, this should lower the mystery ship sound effect:

In the sound board ROM, the volume info for that sound effect is at hex offset $0717
The hex value $0F there is max volume. Lower it to something like $0A to reduce the volume of that sound effect.

It should reset at the start of every ball. It also resets when the ball goes over the collect bonus switch in the shooter lane.

You've got an open circuit on that flipper coils thin hold winding, likely broken from the lug. Carefully inspect/prod the thin wire at each lug and repair. It's not an EOS switch issue.

Not really. Unless your EOS switch mount screws are too long and cut into the coil. Another thing I've seen is new coils come with the winding wires soldered to the lugs but didn't have the enamel removed from the winding wire. Suffice to say there was little or no electrical contact with the coil lug.

Basically when the flipper is in idle down position, the EOS switch is shorting out the hold winding. When you press the flipper button switch, power bypasses the hold winding because the EOS switch is closed across it and so the thrust winding gets full power.
When the flipper rotates to the up position the EOS switch opens and introduces the hold winding on the flipper circuit to hold the flipper up in low current state. Failure on the hold winding causes the flipper to lose power so it releases and results in the the EOS switch closing which now re-energises the thrust winding. This situation causes the chattering/machine gunning.

When you disconnect the windings you then have the opportunity to test the diodes since they will be isolated. The diodes are there to prevent high voltage spikes from back EMF resulting in game resets and that type of thing - they have no impact on flipper function/performance.

Correct, you're only doing the thinner wire. Just carefully scrape a little enamel off the wire at the lug and add solder. Note the thin winding should measure about 320 ohms resistance with your multi-meter.

No.
I have had new coils where the initial soldering of the thin wire didn't burn through the enamel enough and caused poor connectivity so had to be redone.
Before doing this though, for your sanity diagnose it with a multimeter.
Put a piece of paper between the EOS switch on that flipper.
With the machine OFF, measure the resistance between the middle lug and each outer lug. One side (thick thrust winding) should measure around 3.2 ohms, the other side (thin hold winding) should measure around 320 ohms.

The diodes don't affect flipper functionality, their only purpose is to clamp high voltage back EMF to prevent voltage spikes from disrupting the MPU board that could result in reboots / lockups.

I'd suggest your replacement coil is why your problem was resolved rather than being a diode issue.

Any chance you can post a video from the mech side while it's chattering?