I'm having a problem with one of the 7-digit display boards in my Bally Centaur II, part number AS-2518-58. The millions digit is working except for one segment, and all of the other digits are non-working except for that segment (also the commas are not working). The first photo illustrates what I mean.
Occasionally it is possible to glimpse some of the other digit segments lit. The second photo shows an example. So from this I conclude that the display glass is probably ok, the problem must be on the board. I also swapped with a working display to rule out any issues with the MPU, wiring, or the connector.
I tested most of the components on the board in-circuit with a DMM: the transistors, resistors, and diode. All checked out ok. The display glass solder connections looked a bit weak so I redid them all - no change.
Looking at the schematic for this board, there doesn't seem to be a logical explanation for the symptoms. All of the digits use the same segment driver circuitry. Is the problem likely to be the BCD to 7-segment IC, or somewhere else?
Note the "mostly working" digit is extra bright. There looks like some burn in this area.
When I first got the machine, the high voltage regulator and both of its fuses were blown. I rebuilt the HV section, replaced the fuses with correct ratings, and trimmed it to about 170VDC.
Thanks but I already swapped displays to rule out any MPU problems. The faulty display shows the same symptoms plugged in either #3 or #4 position. A good display works properly in either position.
Playable Now: Centaur II, Doctor Who, High Speed. Playable Soon: Breakshot, Sorcerer Later: Flash, Genie, Seawitch Fondly remembered: Firepower
If that doesn't work, try replacing the MC14543LE decoder chip on the display board itself.
The problem migrated with the display which leads me to believe display vice decoder.
On these displays you have a couple of issues.
HV is obviously fine as the rest are nice and bright. The display could be outgassed. The connections are tricky. At the board yes reflow solder both at the display and the connector on the display board. If the connection between the display glass and the pins of the display is bad the only thing you can do is use a conductive adhesive to fix an issue there as sometimes there can be breaks in this area. If all else fails your probably into a new glass.
I recently fixed a 6-digit Bally display that had one bright digit illuminated and only few segments in another, with remaining four other digits dark.
The issue was: - three opened 100K resistors - and, someone had replaced two PNP transistors with incorrect NPN replacements parts at some point in the past. Plus poor soldering too. Hmmm....
Therefore, check for any prior work done by a previous owner - not every one is experienced, knowledgeable and/or careful, unfortunately.
In any case, always fun to troubleshoot and investigate !
Cheers, - Sylvain.
Looking for 1966 Bally Capersville, 1967 Bally The Wiggler, 1981 Stern Viper, 1986 Pinstar Gamatron, 1986 Williams Grand Lizard, 1991 Williams Bride of Pinbot, and a few others. Cash or some trades available. Could also repair a machine of yours +/-$ if needed, in exchange for one machine on my want list, non-working/unshopped welcome!
- and, someone had replaced two PNP transistors with incorrect NPN replacements parts at some point in the past. Plus poor soldering too. Hmmm....
Until recently, there was a sentence on the Bally/Stern pinrepair.com page that incorrectly stated NPN transistors should be used where PNP's are actually needed. I had a heck of a time diagnosing a few displays as a result until I whipped out the schematic and found the mistake. And I've found at least half a dozen displays with missing digits with the incorrect transistor installed. I fired off an e-mail to Clay and he fixed the mistake on the site. I suspect the error sat undetected for quite some time - obvious from the number of previously "repaired" displays using the wrong transistor!
Until recently, there was a sentence on the Bally/Stern pinrepair.com page that incorrectly stated NPN transistors should be used where PNP's are actually needed. I had a heck of a time diagnosing a few displays as a result until I whipped out the schematic and found the mistake. And I've found at least half a dozen displays with missing digits with the incorrect transistor installed. I fired off an e-mail to Clay and he fixed the mistake on the site. I suspect the error sat undetected for quite some time - obvious from the number of previously "repaired" displays using the wrong transistor!
Very interesting, thanks for getting it corrected. I never had used that part of Clay's pinrepair for Bally/Stern 1977-1984.
As a clarification note for MAACA readers, note that the Bally/Stern 6 and 7 digit displays use BOTH types of transistors (NPN and PNP).
From the schematics of a 6-digit display for instance: Q1-Q6 (level shifters) are NPN Q7-Q12 (digit drivers) are PNP Q13-Q19 (segment drivers) are NPN.
Cheers, - Sylvain.
Looking for 1966 Bally Capersville, 1967 Bally The Wiggler, 1981 Stern Viper, 1986 Pinstar Gamatron, 1986 Williams Grand Lizard, 1991 Williams Bride of Pinbot, and a few others. Cash or some trades available. Could also repair a machine of yours +/-$ if needed, in exchange for one machine on my want list, non-working/unshopped welcome!
Thanks for the info guys. I'm waiting on some parts to complete this repair but will report back on the result.
The six-digit display in this machine (credit/match/ball-in-play) suffered from cold solder joints on the header pins. The symptom was faded/flickering digits, and also digits displaying sometimes 1 less than the correct value (e.g. ball 0 when ball 1 should be displayed).
Playable Now: Centaur II, Doctor Who, High Speed. Playable Soon: Breakshot, Sorcerer Later: Flash, Genie, Seawitch Fondly remembered: Firepower
Replacing the BCD to 7-segment chip did not change the symptoms.
After much more staring at the schematic I finally came up with an explanation for this strange behaviour. It seems the millions digit select was always on, causing it to be the brightest digit, and also partly denying power to the other digits.
To prove the theory I removed the millions digit driving transistor, and now the other 6 digits work properly! Just have to order a replacement 2N5401 and it should be fully functional again.
Note: this transistor looked ok using the diode test of the multimeter.
Playable Now: Centaur II, Doctor Who, High Speed. Playable Soon: Breakshot, Sorcerer Later: Flash, Genie, Seawitch Fondly remembered: Firepower
This reminds me of a Bally-35 MPU repair I did last year. It was for a '78 Bally Star Trek game. After the repairs, I installed it in my Stern Catacomb project to see if it would boot.
It booted, but most displays were garbled on the first digit, similarly as tinyrodent`s initial picture. The Star Trek MPU board was good, and the 7-digits were fine with the Catacomb's original MPU.
It also took me a while to figure-out that 6-digit games force the 7th digit data line high, causing the issue. The displays were fine after I temporarily unsoldered the one PIA pin driving the million digit on that Star Trek MPU, or if I installed EPROMs for a game with 7 digits on it.
In my case, the issue was not hardware, but related to the software/game/display requirement type.
Looking for 1966 Bally Capersville, 1967 Bally The Wiggler, 1981 Stern Viper, 1986 Pinstar Gamatron, 1986 Williams Grand Lizard, 1991 Williams Bride of Pinbot, and a few others. Cash or some trades available. Could also repair a machine of yours +/-$ if needed, in exchange for one machine on my want list, non-working/unshopped welcome!
tinyrodent
Male
Logged
MAACA ARCHIVES - JOIN THE NEW FORUM AT HTTP://WWW.MAACA.ORG › General Boards › Tips and How To's › What's wrong with this display?
