Converting a bally 7 digit display to a led display
A fellow pinball collector (Arno Baumfalk) in germany designed a new display pcb for the bally pinballs. This pcb uses 7 segment leds. Here is his homepage .
Here you see a part of his schematics:
We need the following hardware for converting an old bally display pcb:
7 * segment SA08-11YWA 20 mm yellow common anode
1 * ULN2803A
7 * 2n3904
7 * IRF9520N
1 * (elko) cap 220uf
some resistors....
and of course an old 7 digit display pcb...
First I removed all components from the display board except :
4543
resistors r49 - r54
Cr1, cr2
C1
IMPORTANT REMOVE PIN 1 FROM THE MOLEX CONNECTOR , THE HIGH VOLTAGE IS NOT LONGER USED !!!
I found small plastic angles in a local electronic shop to hold the additional pcb in place. This additional pcb will hold the 7 * SA08-11, the ULN2803 and some resistors.
I used super glue to attach these angles to the old pcb.
Mount resistors 22k at the following locations:
r48,r47,r46,r45,r44,r43,r55
Mount resistors 10k at the following locations:
r2,r4,r6,r8,r10,r12,r57,r63
Mount resistor 0r (bridge) at the following locations:
r1,r3,r5,r7,r9,r11,r56
Mount 2n3904 at the following locations:
Q1,Q2,Q3,Q4,Q5,Q6,Q20
Mount IRF9520 at the following locations:
Q7,Q8,Q9,Q10,Q11,Q12,Q21
Attention: Look at the orientation of the legs (IRF9520):

Connect every SA08-11 (pin 11, anode) to the following locations:
SA08-11 position on new pcb resistor number (blue circle, take the hole close to the angles)
1 digit r35
2 r36
3 r37
4 r38
5 r39
6 r40
7 digit r58
Connect Tp1 to location VR1 (take the hole close to the angles) with a wire. (TP2 now also have 5 V)
Connect wires to the base (green circle) of the following locations:
Segment location on pcb connect to ULN2803 pin
a B - Q13 5
b B - Q14 6
c B - Q15 7
d B - Q16 4
e B - Q17 3
f B - Q18 1
g B - Q19 2
dp B - Q22 8
For the prototype I used too many wires for segment control on the additional pcb. I think, If you cut the not used SA08-11 pins (3,5,16), you only need three wires for one segement. I will test this for my next pcb.

Mount the ULN2803 and 8 * 100r resistor on the additional pcb.
segment ULN2803 pin resistor SA08-11 pin
a 14 100r 1
b 13 100r 14
c 12 100r 12
d 15 100r 10
e 16 100r 4 (separate wires for every segment required)
f 18 100r 2
g 17 100r 13 (separte wires for every segment required)
dp 11 100r 9 (connect only segment 7 and 4)
Connect the ULN2803 pin 9 to the ground (you can use the location r42) and the ULN2803 pin 10 to + 5V (use location c2, take the hole close to the angles). Connect the large cap between pin 9 and pin 10 from the uln2803.
Here you see the additional pcb with the 7 * SA08-11, the ULN2803, 8 * 100r resistors and the cap. I don't use a socket for the ULN2803 (because then the chip would be to close to the backglass).
Testing on my testbench....
Here you see my harlem globetrotter:
Let us play...
Some "last words..:"
Modification is done at your own risk !!
Do it only with nonworking (outgased) display pcbs !!
IMPORTANT REMOVE PIN 1 FROM THE MOLEX CONNECTOR , THE HIGH VOLTAGE IS NOT LONGER USED !!!
(If you don't do this you will blow up the 5 Volt circuit with high voltage, killing everything in your pinball !!)
Mail me