Monday November 20, 2017

Repairing Out-Gassed / Weak 7 Digit Display on a Data East Laser War Pinball

Author: Wayne Eggert
Date: 10/16/2010


Introduction
This is a quick description of a straight-forward repair on a 7 digit numeric display on a Data East Laser War Pinball Machine.  Laser War's a lot of fun but it utilizes the 3rd and 4th player displays during gameplay some, especially during multiplayer games when it shows how far players are ahead or behind other players.

Problem Description
I've actually fixed a lot on the machine, it was in non-working condition when it was bought due to MPU board corrosion.  Anyway one of the alphanumeric displays wasn't working and since it was very vital to gameplay I bought another display for $50 on eBay.  The 4th player numeric display was also not working and I determined it was the display itself by swapping with the 3rd player numeric display.

Resolution
There's not a lot to these Data East display boards.  Whereas Bally and Stern had some of the display logic components (resistors, ics, etc) on the display itself, a lot of 6 & 7-digit Williams and Data East displays are just the display glass soldered into a board with a ribbon cable that runs to the master display board inside the head of the machine.  It takes some of the trouble shooting steps out of the equation if a display isn't working and you can just swap it with a known working display.  If the swapped display works then either the bad display is outgassed, has bad solder joints or a connection problem with pin(s) on the display.

I bought a handful of displays off eBay from someone parting out a Laser War machine.  Supposedly 3 of the boards worked (an alphanumeric, numeric and the 4 digit credit display).  Unfortunately I didn't look at the eBay pictures close enough to notice the last two digits looked burnt.


Burnt Digits

Notice the darker / burnt 1s, 10s & 100s digits on the right-hand side of the display


Weak Pinball Display
You can then see when lit up those digits appear weak in certain areas

When digits have burnt segments it usually means either the display was ran at too high of a voltage or some component failed that then forced higher voltage to the display.  Unfortunately a weak display is no good and usually puts a much higher strain on the power supply.  When I plugged this into my Laser War into the 4th player position it caused the 3rd player display to mess up.  I'm not sure if this was from strain on the power supply but even when I disconnected the bad display the 3rd player display was still lighting parts of each digit when it shouldn't have.

7 digit display with burnt digits
Weak display removed from board since it's no good


On many of these types of pinball displays you'll find a glass "nipple" on the back of the display, which is where the factory originally filled the display with gas.  They're not often protected too well so you have to be careful if it's a good display.  The Data East displays in Laser War didn't have this nipple.

Gas fill location on pinball display
Glass "nipple" on back of display

Luckily I had also purchased some NOS numeric displays off eBay so had a new display to replace the weak display.  I desoldered the pins on the old display & then cut the pins to remove the display glass.  Since the pins are so thin they like to stick to the thru-holes on the board and it's much easier to first desolder, then cut the pins and remove the display glass, let the pins that are loose fall out & then just individually heat up any remaining pins with the solder iron so you can easily pull them out.

The board I replaced the display on actually wasn't an original Laser War display board.  It appears to be a Williams Board.  Someone had already modified it by cutting a hole in the PCB for the glass nipple to fit, so I was in-luck with just needing to unsolder the old display and solder in the new one.  If it was the original Data East display PCB, making a hole for the glass nipple would have gone right through a handful of traces.  In that case I would have had to jumper wires across from where the ribbon connects to the display pin solder pads.  So even though this display was weak & it wasn't a great eBay purchase, at least I didn't have to butcher an original Data East board.

Unsoldering old display pins
Pins to unsolder on the 7 digit Williams Display PCB


That's it, pretty straight-forward.  Display doesn't work?  Swap with a known working display.  A non-working display could be out-gassed or it could be a problem with the Master Display Board.  If a few digits are out, it's most likely on the Master Display Board.  If it has weak digits then check if some of the segments are burnt on those digits.




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