1) Look really close in the display. I've seen a lot that are blown (have a physical break allowing the gas to escape) having little white specs everywhere. Just having burns alone does NOT mean it's dead, I have a few really burned that work just fine at 100V, but the more burns, the more apt it is old/and possibly dead.

2) Desolder it and hold the back of it up to a toy plasma ball. Does it produce any orange glow anywhere? If not, it's completely outgassed. DO NOT DO THIS WITH IT ATTACHED TO THE BOARD (it will fry the IC's). Don't believe me, check this thread and video: http://pinside.com/pinball/forum/topic/testing-displays-with-a-plasma-ball

It's definitely burned, and not consistently so (not entire segments) -- that happens when it is burning when the gas is at lower levels, only part of the segment lights and burns instead of the whole thing.

You will notice I only circled SOME spots on the P3 display but almost the entire display, other than some of the center segments, is burned. But at the same time some segments on P1 and definitely the first two on P2 are burned as well, but they are still working. So burning alone does not guarantee death. Partial segment burning and across almost all segments and all digits generally will be an outgassing situation.

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Just buy a new display, desolder the existing one, and solder in the new one. Cost: About $60 shipped for a new one on average ($53+ship at PBL: http://www.pinballlife.com/index.php?p=product&id=538 ). Yes, doing these suck even if you have a good vacuum desoldering station like I do, but the pain is more in the installation of the new one -- getting everything to line up just right before soldering the first lead and hoping the others don't pop out. I've done it 4 times so far on 16 character long alpha displays. These smaller 7 digit ones will be a bit easier. In fact I have to do this same repair myself in the next couple nights on the P4 display. I already have the new glass but have to desolder the dead one first.

Alternately if you dont want to buy a new glass, you could look at finding a used display panel of all 4 (would run typically $125-$150 if all 4 are tested working). But at that point you could look at the ~$200 LED replacement boards instead and sell off this one to someone else at 75% working but used/burned. Note: you have the earlier build of the F14 board with the excess (unused) twist lock light openings on the bottom. This requires a special board due to the different size/configuration of it but PINSCORE makes one.

Yes, just replace 2 zener diodes from 100V versions to 91V versions on the power board. I did that on my High Speed and Jokerz already and will do on my F-14 shortly. It does slightly dim the display but gives them a longer life before they burn out. It does not prevent gas eventually leaking out, but does prevent fast burning of the display segments.

PS: If you do drop the voltage on the power supply, it MAY make one of the other displays too dim to view, and that one too would need replacing. So then it would almost be better to just upgrade to LED and offset the cost by selling the used one. I had this happen on the ball/match display on my high speed -- it flickers a bit on a few segments since it was the most burned, but it's still usable at 91V. The other 4 look fine just a hair dimmer.

I'm in deep on my supposed "complete, working but disassembled" f14 I bought here 6 months ago too. Lots of rare stuff was missing (a reflector/pullies for the center beacon, one of the special hinges holding up the PF, all the clear plastics on top of the PF, etc...) so I know the feeling. Mine was worse as the entire upper playfield was in a single box and I had to reassemble from other peoples pictures online or simply guessing Oh and scrape a layer of yellowed polyurathane off the playfield and level the inserts before even starting! So I feel your pain!

I just finished desoldering my dead P4 and replacing it with a new one. The new one had no nipple. However the leads were about 1/4" too short! To get the most length, I had to basically keep them just level with the bottom of the board, and then solder flat The original stand offs (which all were broken anyway) caused it to be way too tilted out on the top and angled and a bit low on the opening. I will have to use something a bit shorter and just have it a bit more recessed instead. I don't know where mine came from (was included in the box of parts) -- the original had 2 sets of 16 leads, this one had almost half that.. all of the double connections were just a single one of the pair. Everything worked. This one had a weird spiral metal loop inside on the bottom between 2 digits, visible when installed if you are close enough.

Now at least I can see the ball # and a few other things. But of all the displays to go out P4 definitely is the least useful.