None of the scoring LEDs in front are illuminated. Here is a description of the LEDS on the MPU. The top LED named "Blanking" is off. Underneath that the "5 VDC" LED is solid on. Underneath that the Diagnostic LED continuously flashes on and off. If I understand the Williams system 9-11 page (added below) the blanking light should remain on but is not. I have been able to cycle though the diagnostic even though there is no display message visible, reset ribbons, looked for loose connections, visually checked fuses, verified continuity at the battery holder, and activating the SW1 & SW 2 switches to no avail.

Apparently, continuous blinking of the diagnostic LED is expected behavior but I don't think the "Blanking" off is. How can I proceed to repair this game?

Normal MPU boot behavior for games with 3 LEDs on the MPU is for the "+5 VDC" LED to light first and stay on, then a split second later, the blanking LED will light and stay on. At the same time that the blanking LED lights, the diagnostic LED will begin to blink at a fairly rapid pace with a 50% duty cycle (equal durations of the LED being on then off). The blanking LED will continue to remain on.

The game powers up, the play field lights illuminate but not the score panels (what ever these are - not led evidently). Seems like the sound is available at certain times during testing. You can see the new ribbon I tried in the photo to no avail as it seemed the next cheapest thing to try and the old ribbon was really getting crushed with the score panel opening and closing on it.
In the second photo below I believe the power supply can be seen more or less in the center of the photo? To the right of that board is a much newer looking board with the 2 big black caps. On that board there are two green connectors on the left. Those green connectors each have an led illuminated "grd" for ground that is light (expect that is normal good).
CIMG1213 (resized).JPG
CIMG1212 (resized).JPGCIMG1211 (resized).JPGCIMG1210 (resized).JPG

Seems replacing power supply would be a good idea at this point. Haven't been able to locate one. Need a replacement for 11A. Are these available anywhere (pinscore pj-8345-hv)?

Installed the new board. Looks good.
new_board (resized).jpg

Result bad.

dead_score (resized).jpg

New board also missing a connector shown here on the old power supply board. Wonder what won't work if / when this plays again.

old_ps (resized).jpg

What next? Replace the display score https://xpinpinball.com/product/xp-wms10877/

The voltages were measuring zero so I ordered a new Power Supply and replaced the old one. I can't imagine these would still be the issue after the new install. Guess I still supposed to test them.

3J2_voltage_test (resized).jpg
Testing 3J2 pin 1 & 3. Result - 0 - no reading. The red probe was attached to pin 1 and then 3. The black probe was touched to ground (screw & material surrounding the screw on the board) indicated with the black arrow. No reading. The meter is set to 200 V. I also moved it to 20 V after nothing at 200 and still got nothing.

The system 11 wiki warns against installing a new (or repaired) power supply if the F1 fuse is blowing. The F1 fuse is for the display. Since the F1 fuse has never blown I installed the new power supply.

If the test is done correctly it seems still have power supply issue.

I found more information about system 11 game repair here

System 11a, 11b, 11c CPU board LED's.
On system 11a, 11b, and 11c CPU boards, there are three LED's about in the middle of the CPU board. For a working game, here are what these three LED's should be doing when the game is turned on and in attract mode:

Left LED (labeled "+5 vdc"): shows that +5 vdc is present. This LED should always be on.
Middle LED (labeled "diagnostics"): should be continually flashing.
Right LED (labeled "blanking"): shows the blanking circuit is working, and should always be on.

on my game the "blanking" LED is barely lit. The other two LEDs are much brighter. Wonder if that's normal. Wish had observed CPU board behave normally before the trouble started

Transformer in and out? The heavy component at the bottom of the game? Not finding instructions on how to do this on any williams repair pages yet. Hmmm ... in and out from power supply. I did a test of voltage on the power supply testing 3J2 pin 1 & 3. Result - 0.

Cool. Set DMM to 2000mV?

I'm having trouble getting a consistent reading so I'm off to get another 9V battery to replace mine. Not sure how old the current battery is.

Back to retest in a few.

Probed same colored wire to wire
Probed wire and ground
0v for all tests for all wires

I can hear a slight hum, and the lights on the table are lit. I moved the switch to right of off and set to the red V which is AC. I was on the left side testing DC voltage.

Unless you show me your DMM with it's settings and which plugs the probes are placed in the DMM, and how you do one test where each probe gets placed I don't think I know enough to do this properly. I caused a spark by placing one of the probes into the A port and then testing across 2 wires so that's got me scared I don't know what I"m doing. I can follow exact instructions obviously. If I could just know how to do one reading correctly I could check them all. The one pin got a bit of a black spot where it sparked but it was very momentary so I can't imagine any permanent damage would result from that. I moved the red probe on the DMM back into VQMA from 10A (probably should not have placed it into 10A, was supposed to move dial from Vdc to Vac). Are you concerned yet, hehe. I'm trying. Still no readings other than 0 so must still be doing it wrong.

Wish i could fill this in like this guy did
https://pinside.com/pinball/forum/topic/system-11-transformer-voltage

checking out you tube videos on testing a transformer. Looks like I have the DMM set up correctly. Probably just a matter of knowing where the two probes should be placed.
Black com
Red VQMA
Dial 200 V ac

Success. Game is playing again !!!

The new board fixed the display issue. Set me back 160 with a new connector cable and shipping. Seemed like a no brainer since board more efficient, less heat, and new. Most likely the old board's high voltage output was failing because that drives the display but have not tested that.

My bad luck was the new XPin board. Fuse f4 was empty. That is, it looked complete but there was no element across. Since it was a .25 Amp it's hard to see even when present. You can almost tell looking at the picture above where testing new board with yellow DMM. Also, when the board arrived I had to replace f2 with a different amperage fuse because the board gets shipped to support a different set of pinball games. Pinbot takes a higher amperage rated f2 fuse. Also, when I ordered I asked them to send an an extra 10amp fuse so I could swap out f2 when it arrived but they did not. Had to buy an f2 and you have to be careful if you do that at home depot like I did. There are several to choose from. I couldn't tell / missed that the f4 fuse was empty after it arrived. I also move my batteries to the back side of the display while doing the repairs. I have a really, really nice, healthy Pinbot btw.

Even more wierd luck, the f4 fuse on the new board is the high voltage component which is different fuse than the old board. So, since f4 had a defective fuse, after doing the swap, no display score again! Oh man.

If you need help determining your issue I can help you with that. The first think I had to learn was the back side of the transformer is AC, while the back side of the Power Supply is DC. Once you have that figured out you can actually start to troubleshoot various parts of your game using a DMM.

Now, although I'm not entirely certain about all the details in this next paragraph, my pinbot has the mod that reduces problems with transformer harness http://home.kpn.nl/p.koch3/bridge_board.htm. You can see that board installed in photos above. Probably want that mod in your game.