Sounds like U8 chip and socket (blue arrow in pic above) will need to be replaced, as i believe the lack of a 3rd flash is indicating a RAM problem. Very common as it's right in the corrosion area.

As Quench said you got some work ahead of you. Especially now you know the MPU won’t boot up. First thing is to remove ALL the corrosion – both sides. Any corrosion left behind will continue to grow. There’s several methods for removing it from baking soda to toilet cleaner. Remove the IC’s and give it a good cleaning. Look under the green solder mask. Scrape or sand away any loose solder mask and inspect the traces for any corrosion. The back side looks like it may have been affected too. You may have to do some trace repair. Corrosion can grow under the traces where you can’t see it. Also closely inspect any components. Replace any that look suspect. (They’re cheap and easy to replace at this point). While the IC’s are out, look closely at the sockets. Most likely the U8 socket is bad.

U8 and U13 are 5101 RAM chips. And they should be replaced in pairs. I’ve been having problems finding new 5101’s. If it were me, I’d replace them with NVRAM’s. This will also eliminate the need for a battery.

Quench also noticed the corrosion on the headers. To me, that’s the number one cause of failure. As standard procedure I always replace all the headers and crimp connectors on all the boards. Eliminating the corrosion, new headers and connectors and you’re on the way to a game that will last another 30 years.

Be careful and take your time removing components – especially IC sockets and headers. It’s very easy to remove the solder pad. Then you’ll have more work repairing your repair work.

Robotworkshop suggested you put covers on the EPROM chips. That’s a good suggestion. Ultraviolet light can erase the data on the chips. I usually put labels on all the chips so I remember where they go.

Pb1010024 (resized).JPG

You're getting good advice from others here. Restoring corroded boards back to good health is time consuming but if you do it properly they're good to go. It'll require patience, parts, skill and the right tools.

Pinsider @barakandl sells a single NVRAM module that plugs into both U8 and U13 sockets. See the bottom of his web page for the MPU-200 NVRAM - however he's out of stock at the minute.
https://nvram.weebly.com/

Note, he also sells new replacement MPU boards if you're daunted at repairing your MPU board.

I can recommend that dual NVRAM board. Installed one in my Flight 2000 and it works great!

FWIW I've got the "original" MPU-200 NVRAM in-stock & ready-to-ship here:
https://www.pinitech.com/products/stern_mpu200_nvram.php

Also have some diagnostic tools that might help you out if you're doing a lot of board repairs on early Bally/Stern machines. Availability has been spotty on the tools, but I'm working to get some of them back in-stock this year. If you're interested in anything currently unavailable, get signed up on the waitlist(s).

---
http://www.pinitech.com - "Pinball Inspired Technology"
NVRAM, Bally/Stern LED Displays & Mods for pinball machines

He is in the UK, your web page says ....?

SHIPPING AVAILABILITY
This item ships only to United States, Canada & Australia

Oops, you're right.. hadn't noticed he was in the UK.

Looks like he'll have to wait on nvram.weebly to get stock (I see there's no longer shipping restrictions posted on the website).

I ship to the UK but the MPU200 modules are out of stock right now. Been waiting forty five days now for a huge order of the round pin socket mating headers to build more nvram modules. Should have tried a different or multiple vendors and faster ship method. hopefully back in stock soon but I really don't know when they will arrive.

I've never heard of the place myself, but it looks like there's a place relatively close to you that sells pinball parts and does repairs etc. You may want to see if this is something they might be able to help you out with...

http://www.pinballmachines.co.uk

Thanks for the reminder on the tools. I had looked at them before and want to order some to aid in bench testing. They look like they will save a lot of time.

This kit is for Bally & Stern MPU boards including Bally -17, Bally -35, Bally -133 (see note below), Stern MPU-100 and Stern MPU-200 boards.
Contains the following parts that are most frequently damaged by battery corrosion.
The value in this kit isn't just the parts, it's being able to get them all at once from one source.

C1,C2 - Capacitor 820pF, axial or radial ceramic (small yellow bulb, #6 & #7 down in picture above)
C5 - Capacitor 47uF, radial tantalum (small yellow barrel, top of picture above)
C3,C13,C80 - Capacitor 0.1uF, axial ceramic (square brown, upper right picture above)
CR5,CR7,CR52 - Diode 1N4148 (CR52 optional, see note below. Smaller zener #3 - #5 above))
CR8 - LED Green
CR44 - Diode 1N4007
R1,R3,R24,R28 - Resistor 8.2K ohm, 1/4W
R2 - Resistor, 120K ohm, 1/4W
R11 - Resistor, 82 ohm, 2W
R12 - Resistor 270 ohm, 1/4W
R16, R113 - Resistor 2K ohm, 1/4W (See Note)
R17 - Resistor 150K ohm, 1/4W
R29 - Resistor 470 ohm, 1/2W
R107 - Resistor 3.3K ohm, 1/4W
R112 - Resistor 1K ohm, 1/4W
R134 - Resistor 4.7K ohm, 1/4W
R140 - Resistor 20K ohm, 1/4W
Q1,Q2 - Transistor 2N3904 or 2N4401 or equivalent
Q5 - Transistor 2N4403, 2N3906, MPS-A92 or equivalent
VR1 - Diode 1N4738A, zener, 8.2V (alternate for 1N9598)
22 Pin machine socket (optional)
U8 - 5101 Static RAM (optional, various makers) Please note Stern MPU-200s require two 5101s

https://www.greatplainselectronics.com/Downloads/Bally_Battery_Corrosion_Kit.pdf

Gotta love that 'My little Pony' toothbrush!

following this excellent thread.

My F2K is in storage right now but I think I have some pics of the J3 connector on an SD card that I have to look through. I saw earlier in this thread that there were 2 transformers installed. This usually happens when one of the windings (outputs) has shorted or gone bad. Firstly you need to verify that the original transformer is good. If you already stated that, my apologies for not reading the entire thread. Do you remember how the 2nd transformer was wire in? This should tell what they were trying to power up. I would think the GI lamps.

I will search for those pics for you...

That red wire appears to have faint yellow blocks on it. If there's no other obvious red-yellow wires that's probably it.

The Flight 2000 rectifier board schematic (oldschoolbob attached it in post #12 ) shows no wire at J3-13. It was originally used by older Sterns that had the knocker coil in the back box but your vintage game has the knocker in the cabinet (looks like its missing from your game though).

The reference picture of J1 you have is from Bally and their wire color locations were a little different to Stern. Look at the rectifier board schematic in post #12 which shows the wire colors for J1.

F2K doesn't have a knocker. When winning a free credit by match, you get an electronic sound.

Cheers, thanks for the clarification - looks like they ran out of driver transistors on the SDB for a knocker.

This pic straight from F2K. Please note that the J1 connector housing has 8 positions. The newer reproduction rec boards have 9 pins at J1. For F2K, the far right pin is not used. The key plug in the housing should prevent you from installing the connector to the wrong pins. Go to piniwiki.com Bally/Stern section to reference the back side of the rec board solder points and color codes. Sorry I don't have a clear pic of J3, but somebody on this group must. Also get the F2K manual if you don't have it. I have a suspicion that this game will have more issues once she does fire up, so you will need it. Good luck!

P3050578 (resized).JPG

LOL the booze on top. Don't drink too much, we don't want you to electricute yourself! Just watch your vid. Without my game year and failing memory, I cannot confirm what these wire colors are for. At least the knucklehead fused the secondary transformer.

The knocker is a coil with a plunger that makes a pop sound against the inside of the cabinet when you win free credits, hence the term "popping a free game".

SDB is solenoid driver. When you are confident that you nailed down the wiring, don't start the game full blast. Disconnect J1, which goes to the playfield. Take a measurement of the test points and note results. See pinwiki for specs. Also be aware that the score displays get a minimum of 180 volts so be careful where to put your fingers. When the mpu gets 43 volts from the power supply, you should finally get the 7th flash. When testing voltage point, place black lead on any part of the cab ground braid and the red to the test point on the rec board that you want to measure. Don't forget that the GI circuit is AC, so you may need to set the meter for that, all others are DC.

http://pinwiki.com/wiki/index.php?title=Bally/Stern#Rectifier_Board_Test_Point_Values

Make sure you disconnect J3 from the rectifier board aswell!
Only J2 should be connected on first powerup which ensures no circuit boards in the backbox are at the risk of getting powered with wrong voltages.

Measure the voltages at the test points on the rectifier board. If all within spec then you can plug in J3 which hooks up power to the circuit boards in the backbox.

Those particular two blue wires are both power for the feature lamps on the playfield. One blue wire will supply some lamps, the other blue wire will supply other lamps. As long as they're in pins 3 and 7 of J1 that's all that's important.

On the rectifier board, both pins 3 and 7 are connected together and supply 5.4 volts to the feature lamps.
The reason for running two wires is the lamps draw a lot of current so they spread the load on two connector pins/wires.

F2K_RectifierBoard_J1.jpg

No wonder with 5 memory coils and 4 sling shots.

I understand this right up to the point where J3-6 and J1-3 both splice into J1-7 somewhere on the board where all of the load is concentrated. Seems to me that everything feeds off of J1-7 which will be taking all of the load no matter how the wiring is split up.

I also fail to understand why two blue wires are needed on the play field, other than to prevent the crossover of a bare GI power wire string and a bare feature wire string where some feature lights are surrounded by a cluster of GI lights.

I am still learning this stuff. Anything to help my understanding is always welcome.

The mpu connectors and pins are Molex type. Spacing is .100 inch. The connector house is known as a KK style. Usually you can reuse the housings by sliding out old connectors.

Be gentle when replacing the header pins. The solder pads on the board are delicate and even more so after corrosion has set it.

Your rec board voltages seem low. The high volt for score displays should be over 200. Check pinwiki for the nornal no load readings. Tp 5 and 6 look acceptable. Tp 1 should be more than 6 more like 7.3 is normal I think.

What is the normal wall socket voltage for the UK? Are you sure the transformer is jumpered correctly?

It's common for some digital multi-meters to give a reading of about 150 volts when there's no load. There's a number of people posting such a reading here. If you want the true reading you have to measure the other side of the 100k ohm R3 resistor on the rectifier board. Alternatively after you plug in the solenoid driver board (SDB), if you measure around 230-240 volts at test point TP4 on the SDB then you know the high voltage from the transformer is ok.

I was referring to spreading the load across two connector crimp terminal/pins, not how the traces are run on the board.

Below is a chart from Molex indicating the current capacity of their 0.156" (3.96mm) crimp terminals. Maximum for brass is 5 amps and maximum for phopsphor bronze is 7.0 amps. Back in the day Stern likely would have used brass terminals to save cost. With each #44 lamp drawing approx 0.25 - 0.3 amps, if lots/all feature lamps are on, it exceeds current capacity on a single wire terminal connection. So they doubled up.
Having said this it begs the question why Stern didn't double up on the GI lighting at connector J1 like Bally did. I can't answer that.
Personally I would be splicing the GI wires into two and double crimp terminal them in J1 so that that you crimp wire pin 1 to pin 2 and pin 8 to pin 5. Of course these should be trifurcon phosphor bronze crimp terminals for maximum mating contact surface and current carrying capacity.

Molex_0156_Terminal_Current_rating.jpg

I understand what you were saying. I am just having trouble wrapping my head around the fact that all of the feature light wiring from the back box J3-6 and J1-3 all converge on J1-7 which takes all of the load. That is not an entirely correct statement, because according to the diagram
J3-6 and J1-3 come in behind J1-7, so J1-7 pin does not take any extra load, but what ever is on the rectifier board sure takes a hit.

( I hope the OP does not think I hijacked his thread because you sure turned on a light---no pun intended).

OK. When I restored and reran the wiring on my Big Game I elected to use copper foil tape for all of the feature lights. In my ignorance, I ran all feature lights from one copper foil "circuit". That was a mistake. There almost 50 feature lights and they get a little dim when all are lit up. So, I need to breakdown all my wiring and re-do the copper foil into two "circuits" that feed both J1-3 pin and J1-7 pin.

While I am doing this, should I split up my GI wiring and run half of the GI on Pin 1-Red and Pin 5-White and the other half to Pin 2-Red and Pin 8-White? Would doing this allow, or cause, the GI bulbs to burn brighter? It sure would be an easy project to set up.

Thanks