Quoted from Blackbeard:

Sounds like a connector.
You folded the head to transport. Something was likely tight and is pullout out a little. Could even be a specific wire running into it's housing on the board somewhere. I've had wires pull out just a tad from the housing.
I"d put it into coil test, and test the flashers. If they're not working from there, leave it in test mode running, and jiggle connectors on the interconnect and cpu. Try to find the wiring running to those boards associated with the flashers and push the housing AND actual wires back into their housing.
Side question: ever find out what happened to our nice clean ES in harbor creek area last year?

Quoted from edcianci:

i just read this whole thread - if it's a wire wouldn't it be right near the playfield of where the ball is when they go on. maybe the ball hits something on the playfield that just nudges this wire under the playfield to create a good connection/contact for a split second to make them go on. just the thought of a non pinball repair guy - so this might mean nothing. thanks ed

Quoted from DumbAss:

The problem described in that thread was my first thought but your description of the problem does not quite match up. Enter diagnostics and stop the solenoid (coil) test at solenoid #9. The manual describes that as a flasher but does not describe its location. If this flasher illuminates in test but none of the other flashers illuminate then I would suspect the 4N25 optocoupler despite the inconsistency. It's easy to exclude it by a diode test on the IC.

It does not hurt to post them. They might look normal (and correct to you) but someone with more experience and observation skills can spot problems fairly quickly. Make sure they are in focus and well lit. The higher the resolution and clearer the pictures are the better the response will be.
I would start there and see what the results are before going in any other direction.

Quoted from DumbAss:

The boards look clean - including the previous work done on them. Looking clean is one thing. I do not have electron vision. Your camera does not have electron vision. Only a multimeter has electron vision. See below.

That is the correct part. I do not recommend shotgun replacing an IC. If you want to salvage the IC there is potential for board damage if not done correctly. Measure it first. It is measures as "bad" (failed) then definitely replace it. If it measures as "good" that does not mean that it is good. It could be failing under load (in operation). I would replace it after more diagnostics have been performed. If you do want to replace it and have a replacement on hand then use a socket when replacing it. If you want to sacrifice the component then cut the legs of the IC (as close to the body as possible), individually remove the clipped legs and then clean the holes. This reduces the risk of board / trace damage.
https://www.pinwiki.com/wiki/index.php?title=Williams_System_9_-_11#4N25_Opto_Couplers_in_the_Switch_Matrix

Verify the bulbs are good. If they are incandescent then check for continuity. If they are LEDs then use a 9V battery (or power adapter) to check them. Alternatively you can put them in a machine known to work - or take a known good bulb out of another machine.
If none of the flashers work then you likely have a power problem. You will need to measure voltage.
The RED wire coming off the auxiliary power board at 5J11-9 needs to have +25V (nominal). That same RED wire going into the interconnect board at 2J5-8 needs to have +25V. The RED wire coming out of the interconnect board at 2J8-5 needs to have +25V.
The ORG wire coming off the auxiliary power board at 5J11-1 will have +25V only when the A/C relay is enabled for "C" side selection. It should normally measure 0V. If you stop the solenoid test at solenoid #12 the voltage should pulse each time the A/C relay is enabled. Your DMM should be able to detect this pulsing. This same ORG wire going into the interconnect board at 2J5-9 needs to pulse +25V as well. Finally the ORG wire coming out of the interconnect board at 2J8-4 needs to pulse as well.
Finally ... if the RED wire measures correctly then measure the voltage at the flasher lamp socket under the playfield for solenoid #9. It should read +25V.
If the power is present at solenoid #9 you can temporarily ground the transistor tab on the CPU board to see if it flashes.
Check for power first. If you have power then it's the grounding side that has either failed (or is failing to be grounded).
https://www.pinwiki.com/wiki/index.php?title=Williams_System_9_-_11#A.2FC_solenoid.2Fflasher_problems

Quoted from DumbAss:

Does solenoid 8A (Lock Diverter) work?
If it does NOT work then suspect the drive transistor on the CPU board.
If it does then suspect the bulb, the wiring or the 5W resistor on the interconnect board.

Quoted from Blackbeard:

This is a bunch of flashers out, correct?

Quoted from DumbAss:

This rules out the drive transistor on the CPU board. Solenoid 8A and flasher 8C share this transistor.

Visual inspection is good but ultimately the definitive method is to measure continuity using a DMM. I don't have electron vision and I'm pretty sure you don't either.

It does. It's hard to sort through a lot of text, numbers and lists. See below. I hope it gives you enough to be able to sort out issues yourself in the future. Look to see how things are correlated and connected to each other.

No but if the resistor dissipates close to or more energy than it is rated for or dissipates a lot of energy and heats up it can cause a solder joint to crack. In the case of being in excess of rating the resistor will slowly "cook" and will likely fail open (does not measure any resistance across it).

The power for the flashers is supplied by the Auxiliary Power board. If the other flashers work fine then there's no reason to believe that there's a problem with the power supply. It's more likely to be related to the circuitry of the affected flasher.
So here's a detailed description of how to follow the manual and documentation in the manual to find what you need. I hope you find it helpful. Everything below was taken directly from the Rollergames manual.
This is the A/C circuit diagram. Power comes out from the auxiliary power board at 5J11-1, goes to the flasher, to the interconnect board resistor and returns to the auxiliary power board. The components in this diagram and general and not specific to flasher 8C.
[quoted image]
Wiring connection. 5J11-1 connected to 2J5-9.
[quoted image]
Wiring connection. 2J5-9 connected to 5J11-1.
[quoted image]
This is the schematic of the interconnect board. 2J5-9 is connected to 2J8-4.
[quoted image]
2J8-4 is the playfield distribution of "C" solenoid (flasher) power.
[quoted image]
2J12-8 is the playfield return of flasher 8C. It's a BLK-GRY wire. You should be able to verify this is the correct wire color based on the manual description of the location of the flashers.
[quoted image]
This is the schematic of the interconnect board. 2J12-8 is connected to R8 and then from the other side of R8 to 2J4-8. R8 should be a ceramic resistor. Its value is listed as 3 Ohms @ 5W in the manual but the manual specifies values for the early production of Rollergames with the flashers in the back box insert. Most of the production run did not have these flashers installed at the factory so the value of the resistor may be different due to the different number of flashers on the 8C string. Check for continuity between 2J12-8 and R8 (check which side by looking at the traces on the board) then check the other side continuity to 2J4-8. Alternatively you can measure resistance from 2J12-8 to 2J4-8 and it should measure the same resistance as the value specified on the resistor (presumably 3 Ohms).
[quoted image]
Wiring connection. 2J4-8 is connected to 5J5-1.
[quoted image]
Wiring connection. 5J5-1 is connected to 2J4-8.
[quoted image]
And finally the auxiliary power schematic for the A/C flasher drives. 5J5-1 is labeled as 8C and passes through D44 before being grounded by the drive transistor on the CPU board - that we know is working because solenoid 8A works. Verify D44 measures correctly.
[quoted image]
That's it. That's how the flasher is controlled. If there's a problem it has to be somewhere in that path. Note that playfield wiring is not fully pursued here and if you suspect playfield wiring then use a DMM to verify continuity between the power wire (ORG) and the drive wire (BLK-GRY). Also note that using an LED will not allow you to measure continuity. Remove all LEDs on the string and put a single incandescent bulb to perform this test.

Quoted from Blackbeard:

robin
The info above should be stickied some how.
Something to contemplate. It’s amazing information most have no idea about.
Well done DA. Well done.

Quoted from Blackbeard:

Did you ever figure this one out?