Hello,

We've got an old Zaccaria Pinball Champ '82 which CPU Board was a total mess. So we decided to bring the machine back to the future and replace the board with a Raspberry Pi and our own circuit. This works well with Interface- and Soundboard, which we can drive however we want, but currently we just can't figure out how to drive the old displays.

We know we have to strobe them and writing a number on a single 7 segment is pretty straight forward by writing the BCD number to pins D0-D3. But this is everything we can reproduce constantly. We guess (know?) that A0-A2 is selecting one of the eight 7 segment displays. But there things begin to become strange. We just don't know is what this D-Latch (IC2 - 4042) has to do in this circuit and we figured out that run has always been set to low and the next number is written at the low high transition of S1-S6.

But the behavior of the displays appears to be just random. On one displays we can write digit for digit but sometimes other displays are reacting too and on other displays there are always multiple (2 or 3) digits lit at the same time without changing any pin states (which, what we understood from the datasheet of IC1 (4028), should not even be possible.

Does anyone have any clue on how to set the pins in which order to light the display segments one by one?

Thanks in advance

Display_Board_Schematic (resized).png

Hello,

Just for sake of completeness we found the solution to our problem.

You got to switch Pin RUN to zero, provide a number to IC3 and then select a segment with pins A0 to A2. Afterwards it needs a transition of high-low-high on the display select pin 1-6 and the number is shown on the digit.

The strange behavior came from the gas tubes 2 segment digits not working which totally messes up the whole circuit, like showing multiple numbers at once (which shouldn't be possible) or reversing the sequence of tubes that are led.