(Topic ID: 207905)

Display problem devil's dare

By d0nutZ

6 years ago



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#4 6 years ago

The wiring diagram, concerning the players scores displays, is basically the same for all SYS80 games. For SYS80A, like DD, there is no much difference except they add an extra digit. As ForceFlow said, a common group is used for segments of 2 displays.

But what's funny about the DD is that score displays are not labeled ! There is no mark on the backglass to indicate where is the score of player 2, or that of player 3. They could very well be arranged horizontally or vertically. On the DD, they are arranged horizontally and can be easily identified with the label of the connectors. So, the problem on your DD is for PLAYER 3 and PLAYER 4 displays.

Looking at the schematics (here for a SYS80, but similar for SYS80A), you can easily identify that the culprit is the B group :
2018-01-21_09h10_00 (resized).png2018-01-21_09h10_00 (resized).png

On the A1 CPU board, you can see three groups (A, B and C) of components for segments.
Each group use two IC : a 74175, that is a latch (memory) and a 7448 that is a decoder (BCD to 7-segments).
As, only the group B is faulty, the defective component could be Z20 or Z21:
2018-01-21_09h10_51 (resized).png2018-01-21_09h10_51 (resized).png

May be the issue could be "storage" (74175) or "decoding" (7448). But, as only the "c" segment is lit, and as the 7448 has not this configuration encoded, this mean that the Z21 is toasted.

Note that, most of the time, the 7448 burned because someone plug/unplug the display when the pinball is powered. Doing that, most of the time, a high voltage (60 volts) can return to the logic IC and destroy them. Always turn off the power before doing anything on connectors.

Replace the Z21 - 7448 on the A1 board (and use a high-quality socket - tulip).

The 7448 is a chip that is sometimes difficult to found, because obsolete and no more produced.
A good alternative is the 5448 (the military version), which is oddly, almost easier to find.
The LS version (74LS48 or 54LS48) can be also used - no more produced, but at least 4 manufacturers had made it (Texas, Motorola, National and Hitachi). There is no HC (or HCT) version of this chip.

#6 6 years ago

On the 7-digits modules, the comma is driven by the Z3 (7432) chip.
Z3 is used to detect if a digit is displayed or not (by checking segments a, c or h).
If the comma is locked on, replace Z3 on the module.

To be sure the problem is from the display module, you can also try to interchange modules of player 3 and 4 (or any other).
If the problem move to player 3, sure the display module is the culprit.

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