Recently picked up a Williams blackout and thanks to many people on this forum I've got a lot of The kinks worked out! I am however still having trouble with the displays and scoring. I have 2 good displays in the player 1 and 2 positions. The other two went to the trash. Neither of them worked on any harness. All the harnesses do work and show the same error of missing digits on each one. At one point all the digits were there and then only two on the far left and now the two in the center are missing. so it seems like every time I turn the machine on the zeros move positions, reappear or disappear in various spots on the displays. However the master display looks like it's correct with double zeros and it does credit up showing 00 01. I'm a novice yet so I'm not sure. So the displays need some help and after the game boots and kicks out a ball, hitting anything like drop targets or stand-up targets will reflect no score in the displays. I have ordered a capacitor diode repair kit for my power supply and since I have no sound I also ordered the repair capacitor kit for the sound card. (I'll tackle sound last). I have included some pictures that may help. the repair kit should be here in a few days but in the meantime I would love someone to tell me what to check and how to check it I do have a multimeter and I'm very good at using it if someone can guide me. I'm also very good at soldering and desoldering components from a board.

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Repair kits arrive Thursday.

I don't have a logic probe. The MPU and Driver board were serviced last week and put on a test fixture. I was told it ran for two days with no issues. Not sure of this. I'll try to be as accurate as I can...here's the latest. I'll number them in case anyone wants to address anything using a number...
(MDB=Master Display Board)

1. The game goes into attract mode upon power up.
2. The game credits up and 00 01 appears in the Master Display. The knocker coil fires, but weakly. I put a 23-800 coil in place of a 23-900 coil. Would that be the cause of a weak plunger knock? Game advances thru 5 balls. Game ends and a two digit match number appears on MDB.
3. Game starts but no sound and no scoring when targets or anything is hit. Just a loud hum in the speaker. Feature lamps seem to function OK. Hit a target and a lamp goes out or a flashing feature lamp with go steady ON so this seems fine.
4. ALL coils work but are weak. Likely why the knocker coil is weak. Kickers are at like 40% kick and that ball should fly off the 3 bumpers.
5. All 4 player harnesses have power. 2 of 4 displays seem functional. I removed the 2 dead ones. They didn't work in any of the four positions. Moving the good displays around reveals the same missing digits on the displays. One day the center two digits are out, another day only the two far left digits are on etc. At one point all 6 zeros were up! I did a continuity check on every wire from the Master Display board to the back box. All good. I re-tinned all connector pads on the MDB. No change.
6. A capacitor repair kit for the power supply with heavy duty diodes and a sound board capacitor kit will arrive in a couple of days.
7. Coin door controls show that The G.I., the solenoids and bookkeeping functions seem to work. Of course the display test goes crazy. The rotation of 111111, 222222, 333333, etc has never been seen yet.
8. A major breakthrough today: A friend of mine is giving me a working matching Master Display board from his Time Warp tomorrow! This will undoubtedly save me hours of troubleshooting. Before I plug this in and try it should I wait for the Power supply repair kit? Or won't it matter. Any advice here on how to proceed after installing it would be very appreciated. I don't want to harm his MDB in any way and I'd like to get the best results from the test.

Thank you to everyone who has helped me in the journey thus far

Yes the MDB shows ball in play one through five and then game ends. Two digit match also appears. Most likely I will try this this week and report back. Thank you both for the input I really appreciate it! I'm just worried about the weak coils. Could that be power supply related?

Actually ALL the coils are weak. Same weak out put from bumpers, kickers, knocker, drop targets, etc. I measured 20.1volts at pin 6 of connector 3J4. According to flipper.com this should read 28 volts and should point to a bad bridge rectifier in the back box. In the picture it shows two of them mounted on the backbox wall and I believe it's the left one with the red wires connected at top and bottom. Does that seem feasible or should I wait for the power supply kit before purchasing a new bridge rectifier? Part 6BR2 I believe. Voltage test has 36V on the double wire + side, 14 volts on top red wire, 14 volts on bottom red wire and 0 volts on the - side.
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I assume you mean set my multimeter to DC not AC because I do get 36 volts from the double wire plus side and 14 volts each on the top and bottom red wires. I get no readings set to AC.

Okay installed my friends Master display board and left my power supply in there no change same digits are missing same flashing every now and again. He also gave me a power supply to try and when I put his in I started getting some positive results. The digits are still flashing and messed up in the display but you can see that it's scoring now every time I touch something on the playfield the score display advances (2nd photo)not all the switch rollovers work but at least we have some movement here. His MDB shows two digit credits and counts ball in play like mine did. All the coils are still very weak like they were yesterday. I'm thinking his power supply isn't all that great either or something else is not right. Still getting 18-20 volts at pin 6 at 3J4 with his power supply rather than 28 volts. Any theories?? Things are better with his power supply. Repair kit almost here. Oh, and I'm getting 36VDC at the solenoid bridge in the backbox.
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Just put my power supply back in after reflowing the pins and reflowing some other components and I'm getting better performance than his. (See pictures). Almost all digits are illuminated now... if you look close enough it's like half power on one of them and it occasionally winks out. I reinstalled my MDB as well and things still look better! So it appears for the time being that my MDB is functioning correctly. Of course Mr Spock would say that I don't have all the facts yet. But I'm pleased with the progress. Scoring is still happening for the most part. The score displays show a leading zero even though you're in the tens thousands I always thought that that zero was dark until it was needed in the hundred thousands.

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Will do sir! I had the meter set to AC the other night to check that bridge rectifier and didn't get a reading at all. I had the black lead on ground and touched the red lead to all four wires and got no reading was I doing it wrong? I only got readings on the DC setting.

Just refinished flowing all the pins on the driver, mpu and sound boards. I have to say that the digits in the displays look a bit brighter but still missing one digit in the center of the display. No sound. Machine still credits up and scores but all coils still weak and 20.1 volts at pin 6 of 3J4 on the power supply. Installed my friends known good MDB again after the reflow of pins just to see if all digits would appear. No change. Rebuild kits arrive tomorrow. Will install and report. Any advice on the 20.1 volts and where to check and what to replace to get the coils to 28 volts would be very appreciated!

Same 20.1volts at pin 6 with my friends power supply. I'm sitting down and rebuilding the power supply and the sound card right now....

Okay replaced all the capacitors on the sound card, replace capacitors and diodes on the power supply, the horrific buzzing is now gone from the speaker but still no sound and the display issue is still there so no change on the displays. The game does boot up it, has a nice attract mode, game starts, counts balls match lights up at the end of the last ball, scoring looks ok but the coils are still weak 20.1 volts still at pin 6 at 3J4. Any ideas what else to check for the weak coils and how to get that up to 28 volts? Any ideas for the score displays....? One missing digit, one weak digit....

I tried using the AC setting on my multimeter and I'm only getting 28.5 volts on that backbox bridge rectifier between those two red wires!! Could that be the issue with the weak coils? Also only getting 9.9 volts AC at 10J1 on the sound board wire harness rather than 18 volts as the guide says.

Hundreds display digit missing when game is first turned on. After a few minutes all digits are on! Ideas?

You mean all the female harness connectors going to the MDB from the backbox?
And new pins coming out of the circuit boards? I have not replaced those. I have re-flowed every single pin and cleaned each pin. I've seen a Molex connector kit with strips of pins that you can cut to length and piles of crimp-on female sleeves for the ends of the wire that slide into the plastic Molex connector housing.

Understood. Thank you...