Ok hopefully some of the guru's around here can point me in the right direction!

Here's the deal - I got a killer Taxi, she's in great shape and I'm finishing the resto on her right now. I've got everything in 100% shape, except for this:
2014-04-28 21.08.58.jpg

Here's what happened... Display was working great, and then I hit up a HS of 10.6 million. While the machine was whooping and ringing and flashing (massive amount of voltage going on!) these segments suddenly lit up and have not gone away since. It appears that ones on the right are always on no matter what. The ones on the upper left (hard to see in the picture because of the score display) only seem to show up when the Jackpot is flashing - and then they "flash" along with the secondary display - which also displays a weird lit segment in the same place. Don't worry about the bottom row, it's fine, those are just some segments starting to light when I took that pic. I'm hoping that gives you guys a clue as to which chip may have burnt. The displays themselves are fine, dark black with no gassing - and I'm really hoping that I can find/isolate the correct part and solder in a new one.

Any ideas, O Great Collective??

Yes, yes I did.

Thanks for putting this on here, I hate cross-threading stuff - which is why I created a topic. Let's continue on this one so we don't create a bunch of confusion, cool?

Ok I got a source on a 4050 and UDN7180. I'm going to try to test those now and confirm, and will order them up if I can determine that's it. Even if I can't narrow it down 100% to those two chips, (I don't have an oscilliscope only a DMM) I'll probably order them anyways and, as you say, "shotgun replace" them. $25 is a small price to pay to get my pristine OEM display back!

Seriously man, thank you for all your help. You've given me more legit info in 15 minutes than 2 days of fumbling around schematics and searching the internets high and low!!

Yes, I've already swapped the ribbon cable (back and forth from both machines) - it works fine in PF and the one from PF does the same thing in Taxi. CPU is testing out fine, everything else looks good. Judging from the way it "went" I think it's a fairly safe bet that one or both of those chips blew out. I'm going to swap the entire display board from PF over to Taxi, just to verify that it's not a CPU issue. Once I do that, I'm pretty much down to those two chips, right?

Ok this is interesting... Just took the whole board out of Taxi and put it in PF.

It worked perfectly - no lit segments, just like it should. I'm going to pop the PF board in Taxi just to double check, but it looks like it may actually be a logic/control problem and not a burnt 7180.

I'll post back in a few with the results.

WHY did Williams insist on using these backless, push-in style receivers on half their stuff? Grrrrr...

PF's display is secured with 9mm nuts and black standoffs on the front of the backboard, with a slotless bolt on the back of it. Two turns on the nut, and the back starts to spin freely with nothing to grab or push on to loosen the nut!

I'm just going to wait until I hear back from you dewdude, instead of ripping apart a perfectly functional, original display board unless I have to. I'm not afraid of putting in the work, I'd just rather not risk something old and original breaking while moving stuff around testing it, if we already have the info we need. If it was a chip on the display board - no way it works 100% on PF. Right?

Do you think it's necessary to put the PF display in Taxi or should I just move on to troubleshooting the logic end of things?

OK here are some more pics of what's happening. The segments on the right hand upper side (player 2) are on constantly. The segments on the left (player 1) flash in accordance with the jackpot display. If that secondary display isn't flashing, like while in meter mode, the segments are not lit.

Here you can see - the secondary display is scrolling (not flashing), and the P1 segments are dark.
2014-04-29 13.35.19.jpg

Here it is again, this time flashing the jackpot value - and the segments are lit. You can see they are just coming on, they flash with secondary display.
2014-04-29 13.35.21.jpg

This is part of the same sequence - here the secondary display is totally dark, as are the P1 segments. This is between flashes.
2014-04-29 13.35.16.jpg

A split second later, the jackpot amount lights up again and so do the P1 segments.
2014-04-29 13.35.08.jpg

Thoughts, gentlemen? I'm all ears!! Maybe this is tied into one of the secondary display power circuits?

Possible culprit? I just went thru and pulled, checked, and reseated every ribbon and molex connector between the display, PSU and secondary power. It all looked pristine, as it should since it just got a professional shop job a few months ago.

In pulling the display ribbon from the control board, I noticed this just above the batteries. Now, this whole area was worked on and the battery holder replaced and some work done to repair minor corrosion. This is directly above the batteries, where the ribbon connects. Look under SCR4.
2014-04-29 13.58.57.jpg

Thoughts? If I'm not totally mistaken, that sure looks like 9 on the ribbon cable, which would be the segment in question.

dewdude, now you see why I'm starting to lose my mind over here!!! :/

I just pulled the receipts. Brady Distributing went thru this thing top to bottom, re-worked the battery backup and surrounding board areas, and put in a new power control board. Receipt is dated 4/15/14, and I think I'm gonna give them a call and see what they say. There has been some major work done to that board and I don't have a breakdown of exactly what was done, making it double hard to troubleshoot. If it's still under warranty from the work the previous owner had done, I may have to bite the bullet and take it down to them. If I knew exactly what the problem was and I could replace a couple of components and be done with it, I wouldn't bother but unless you can come up with something that I can test over here, I'm pretty stumped. If you need a copy of the wiring I can send it to you. I have a hard copy (missing the last few pages with the critical schematics I need, of course) and I pulled a pdf down from ipdb which has all the pages. Just hard to read those split pages on a 14" laptop monitor!

Thanks again man, can't tell you how much I appreciate you putting some thought into it!!

Just got off the phone with the technician who worked on the machine last month. He essentially confirmed everything that I thought... battery corrosion in the board traces leading up to the display output. He said he did a bunch of work on it and got it the best he could, but that he couldn't get it 100% and that's as good as he could do without a full board replacement.

So... yeah. Looks like I'm in the market for a new Sys11b board. Unless there is a way to fix it? I don't mind spending time and working on delicate stuff if there's a way to rework it.

Yeah the rest of the machine is in spotless shape. He's a trusted tech and I take him at his word. He did a fantastic job overall. It's definitely those SR2/5 connections. I slightly wiggled them to see what was up and when I rebooted, the left side is not flashing, and two of the segments are constantly lit (instead of four or five which flashed with the jackpot display). I may try to replace those traces at some point down the line. Theoretically, if I replaced just the 2-3 traces that are fried with wirewrap, that *should* do it without re-wiring the whole thing, right? The game plays perfectly and I just spent a bunch on new ramps/plastic/rubbers so I'm probably just going to deal with it for the time being. I'll be placing a rottendog board on my list. Heck, a replacement display was going to be $200+, $350 for a whole new board on a keeper pin isn't really that horrible in the grand scheme of things, right? (I just keep telling myself this, over and over...)

Yeah, the game is 100% functional with no glitches or errors, except those segments that want to stay lit. Not bad, and I know the previous owner had over $700 in it with Brady last month. The tech gave it his all, he knows what he's doing, and if I have to live with a couple lit segments that don't effect the gameplay until I can save up for a new board, so be it. To me, this table is well worth it. Even factoring in a new board, between the ramps, plastics and rubbers, I'll still have less than $1500 invested in it. I have no problems ending up with a gorgeous, completely shopped Taxi with a new MPU for that price.

Just got back from the shop - this board been given all the life it's gonna get. With another Sys11 in the house (Police Force) I'm going to be better off in the long run, picking up a new rottendog and keeping this one as a working backup with a wonky display thing that I can always fall back on if something happens to either one down the road.

Good to know, schonb25! It'll likely be a few months, but I think a rottendog is definitely in my future. I'm planning on keeping this pin for a (life) long time, so putting some money into it here and there doesn't freak me out, I'm not trying to flip it and long term, this is the better fix. It's worth it, IMO.

Weird. I started it up last night, and no lit segments. After a couple games, the slowly started to fade back on. For the rest of the night, they randomly would pop back on for a game or two, then go back off.

Pretty sure something the tech re-traced on the board got hot enough to slightly loosen/soften the solder and create an intermittent short - and I think is has something to do with that strobe circuit dewdude was referring to. Hopefully, I can get that board out and clean up the excess and get this fixed for the time being!

Yeah, seems like you are having the same issue. Battery corrosion right where the display traces lead to the ribbon cable, underneath the and around the battery holder.

Good luck. I haven't pulled the board yet, my segments fade in and out randomly and I'm not going to risk messing something else up attempting to re-trace something that minor which doesn't really affect gameplay. Eventually, I'll grab a rottendog and be done with it. In the meantime, I just deal with it whenever it starts up.

Cool, gonna check that out today!