EDIT -- RESOLUTION: Verified Rectifier Board Connector J3 Pin 8 was providing 11.9V, verified wire (when connected) at Pin 8 was showing the voltage too. Followed wire to other end -- a connector on the SDB, and found the end of that wire was fraying/broken and coming loose from the connector pin. I popped it out and re-pinned it, and now it works fine!

_______ORIGINAL POST BELOW________
My original problem child has reared its ugly head again. It figures, as I have out-of-town guests coming in tomorrow, and a party/tournament coming up on the 23rd.

Anyway, went to play a game on each of my pins tonight to verify all's well ... everything was going great until I got to my Bobby Orr Power Play. GI comes on, but didn't appear to boot up. I opened up the backbox, wondering which error the MPU's LED was going to show me this time.

Well, the LED showed me nothing. Nothing at all. No flicker, no flashing.

I checked all the fuses on the rectifier board; they're good. I disconnected / reconnected all the connectors. No help.
I flipped through the troubleshooting guide I'd printed out, and it mentioned to check the voltage at the MPU's TP2 -- which should apparently be 12V. I'm getting about 1.3 volts, so this seems like a good clue.

It's very late, and I'm overly tired ... maybe I'm missing something simple, but I can't see straight anymore. I won't have much time to work on it tomorrow, as I have to prep the house for guests ... but I thought I'd just throw this out here for some quick troubleshooting assistance, in case I have a few moments to look at it.

(One of these days I'm just going to have to bite the bullet and get an new MPU. This MPU had a fair amount of corrosion damage but I've had it working fine for quite some time now. In fact, I played it as recently as Monday with no problem.)

Anyway, thanks in advance for your help / recommendations...

I removed & cleaned up what I could after I first got it, and that was able to bring it back to life. Periodically, though, it'd go down again, so I'd do a little more cleanup (maybe some areas I'd missed or couldn't get to) and then it'd come back to life again. In all these iterations, though, even when apparently knocked out, the LED would still always get into the flicker/flash sequence. This is the first time I've ever had it not even get to the first flicker. That's why I'm wondering if there's something else that could be affecting it.

Thanks, sorry it took me so long to get to this.

Firstly: Fuse F3 is good. Swapped it out with a brand new one to be sure.

Next: I don't have 5V on MPU TP5. See below for voltages at test points.

Here are my voltages on Rectifier, SDB, and MPU. Note: I'm comparing to the values found at http://techniek.flipperwinkel.nl/ballyss/rep/index1.htm#tp ... "s/b" = Should Be.

Rectifier TP1: s/b 5.4 ... is 6
Rectifier TP2: s/b 235 ... is 230
Rectifier TP3: s/b 11 ... is 11.9
Rectifier TP4: s/b 6AC ... is 7.3AC
Rectifier TP5: s/b 45 ... is 43

SDB TP1: s/b 5 ... is 0.34 ***
SDB TP2: s/b 190 ... is 187
SDB TP3: s/b 5 ... is 0.35 ***
SDB TP4: s/b 230 ... is 236
SDB TP5: s/b 11.9 ... is 1.3 ***

MPU TP1: s/b 5 ... is 0.35 ***
MPU TP2: s/b 11.9 ... is 1.3 ***
MPU TP3: s/b 21.5 ... is 21.8
MPU TP5: s/b 5 ... is 0.35 ***

As you can see, rectifier voltages appear nominal, but the 5V and 11.9V test points on the SDB and MPU are coming back way low. Please advise. Thanks in advance!

Checked pin 8 on Rectifier J3 -- 11.9V.

Plugged back in J3, powered up, and machine came back to life! Odd, as I wouldn't think I'd have problems there -- a few months back I repinned all three of those connectors (board side AND connector side) on the rectifier.

THANK YOU!!!! I'll call this resolved. If you have any input on why you think this may have happened, to prevent future recurrence, I'm all ears.

Just as an FYI for people who might find this thread later for similar troubleshooting ... this problem reared its ugly head again. I continued following the path we'd started above; the wire coming off Rectifier Board Connector J3 Pin 8 was confirmed to be getting the proper ~11.9 voltage ... so I followed that wire to see where it went next. It ends in a connector on the SDB. So I pulled that connector and found the end of that wire was fraying/broken and coming loose from the connector pin. I popped it out and re-pinned it, and now it works fine!

Great! Glad I was able to help. This community has been so helpful for me; I'm thankful I'm able to give something back occasionally.