Quoted from Michaelxwhite:So....you're saying replace u7 on the Mpu? What could of caused it to go? Unregulated current from old power supply? Have you heard of a chip crackle and pop before with no visible damage?
Just a guess based on symptoms (no displays, flipper issue) and U7 being involved there.
That said, looking at the manual, the 6th flash happens after the software tests U7. Not sure how extensive the test is. It was just a thought if you had a PIA to throw in there, since U7 is in a socket it'd be an easy enough test.
As far as testing the displays further, well, there's test points on the back for 180VDC and 80VDC.. if you had alligator clips you could measure voltages there, but definitely need to be careful hooking things up on the back of those and don't want to handle the displays while you're testing them. High voltage sucks.
There's no +5v test point on the back of the displays, but that you could test with the POWER OFF to the game. You'd have to find something that 5v is feeding on the display (ie. one of the logic chips on the display) and then use continuity test on your meter to a 5v test point on the MPU to see if you get a beep.
At that point you'd rule out any voltages not getting to the displays and be left with display signals. Now if just a single segment didn't reach the display, or just a single BCD line.. you'd probably still get something out of the display. But if it's a latch/strobe or all the segment data isn't hitting the display.. then it wouldn't light up. With both displays affected, and no blown components on the back of the display, and an orange glow out of them.. and an MPU that looks pretty decent, I was just thinking U7 looked like it was involved.
This is then where a logic probe would help.. since you could probe a few things back at the MPU to see some of the low voltage signals are being generated for the display (digit enables, segment data, latch, etc).
If you haven't already, try reseating the display connector on the MPU.
I hate to throw too many things out there, but I also came across this post talking about D23/D19 going bad..
https://pinside.com/pinball/forum/topic/need-a-bally-6803-exper
D23/D19 are diodes in the flipper enable circuit. There's part of the schematic shown in one of the posts.. maybe check those diodes? They should be near the relay at the top right of the MPU I would think. With the flipper short having occurred, maybe back EMF did affect something in that flipper enable circuit and got back to U7.