Bally low cost led displays. 6 and 7 digits.

I was already thinking about a led display for any pinball, When in oktober 2003 the schematic for such a display was published on the German site of baumfalk. During the same month Oliver Kaegi made a working display using that schematic,( see his website ) he mounted the whole on the original Bally display board. All this together brought me the idea to use the original Bally board and adapt it ( change only 7 resistors and 7 transistors) and then just replace the glass display by a look-a - like led display.Perhaps the color of the display will be a bit different, but life time of such a led display is enormous and the price is ridiculous low..Together with an easy to install factor this could be interesting for now or certainly for the futur where glass display's will disappear.

First i had to find out how much place i had to mount and to make the actual display's.How to mount the PCB board and so on. Photographs say more than words..

Simple aluminium pieces to fix the new display bord.

A PCB was made with the same measures of the original glass display.

The design of the 6 digits display PCB , using cheap single sided print material. I'm looking out for someone to make this printed circuit. You have to mount the display's yourself and drill all the holes! One can use any display type, the only conditions are that the common anode pin is the first upper pin at the right, and the dimension: 20mm large..

The design for the 7 digits is similar , just one more, we use slightly smaller display's type MAN8610 of 18mm.

The 7 digits print.


You can use any display but the common anode has to be on the first pin right looking to front of the the display.The segment connections are adapted when connecting the display PCB to the driver board.Once you have a PCB the only thing to do is to solder the 6 ( 7) led displays on it, and to connect the 13 connection points .

There are 7 (or 8 ) connection point for the different segments named; a,b,c,d,e,f,g and for the 7 digits display add to that the decimal point.And another 6 or 7 connections for the common anodes.,

Connections for a 20mm display type HDSP 3400.

Connections for the MAN8610 display.

I recommend the MAN8610 as it is orange . Here the datasheet .....

There is a difference between the 6 digits display boards and the 7 digits display board!!

For the 6 digits the connections are as follows; a goes to pin 2, b to pin 4, c to pin 6, d to pin 34, e to pin 36 , f to pin 40 and g to pin 38 . The common anode for the units goes to pin 3, for the ten's ,to pin 9, for the hunderd to pin 15, for the thousands to pin 25, for the thenthousands to pin 31, for the hunderd thousands to pin 37.

For the 7 digits the connections are as follows ; a goes to pin 1, b to pin 3 , c to pin 5 , d to pin 33, e to pin 35, f to pin 39 and g to pin 37. there is one line more the dot line that goes to pin 13. The common anode for the units to pin 2 , the tens to pin 8, hunderds to pin 12, thousands to pin16, thenthousands to pin 26, hunderdthousands to pin 30, millions to pin 36,

Working without "special" printed circuit !!

That can be done to, i made a 7 digits display , as an example, for a Zaccaria . Look at the page Zaccaria 7 digits display for a complete image and " how to proceed" . For Bally it is the same .

Use a piece of universal print.

Mount the displays.

All segments connected together and the oragne wires are the common anodes.

The display is ready!

Working on the bench!!

The original Bally board has to be adapted , to work on 5 volts instead of the usual 190 volts.Let's take a look at the schematics to find out the differences.

You can download the complete original Bally 7 digits display schematic here.....

The 6 digits schematic here ......

Here the part that drives a segment ( f in this case) The resistor going to the 80 volts is eliminated, the resitor to ground is eliminated to , and replaced with a jumper.And the resistor steering the segments display is reduced in value , putting in a 100ohm resistor. The transistor is replaced with a BC140 or equivalent ( not critical).

The selection of the different units . The 190 volts is subsituted by 5 volts , the resistor to ground is cutted off, and the resistor of 100Kohm is replaced by a jumper.

How is this done on the actual board?

On the Bally board ( and on Stern) all componentes are numbered and the number is printed on the PCB. We start by changing 7 the transistors by BC140 's (or replacement type) that are; Q13,14,15,16,17,18,19. Put jumpers at the places of resistors R33,32,31,7,9,11,30,29,28,27 and two 100 ohm resistors at R25 and R23.

Other changes are; cut resistors R1,3 and 5 and place jumpers instead.And in the row nearst by the former glass display, cut resistors R35,36,37,38,39 and 40. Replace R13,15,17,19 and 21 by 100 ohm resistors.,

Last thing to do, is to desolder pin 1 of connector J1 and connect the run with pin 20 , this brings 5 volts on the place where was the former 190 volts., the fact pin 1 is removed inibits the 190 volts to reach the transformed display board.

Another solution is to connect the soldering point of former pin 1 to a separated power source, such as a simple black feeder block, use one where the voltage can be selected between 5 and 12 volts. This solution gives the possibility to adapt the brightness of the display, Higher tension is brighter display, 9 volts is extra bright...Also this solution put no extra load on the excisting 5 volt power supply. Altougt things work very well with the first solution and using the excisting 5 volts power supplie.

7 position display board.

For the 7 position board we have a few more resistors and jumpers . Extra's are;

Jumper in place of R56 and R60. Remove resistors R58 and R62. R61 is replaced with a 100 ohm resistor, and Transistor Q22 is replaced with a BC140.

Stern display's.

The numbering on the Stern display boards is luckely the same as on the Bally boards.

Final result.

The modified Bally board mouted with the new pbc for 6 display's. Not to much wires in the back thanks to the pcb. You see clearly the new BC140's in the middle row.

The front site.

The working unit, on test bench..

The new display will draw more current from the 5 volt alim of the pinball... This problem is not mentioned at the baumfalk site or by Oliver Kaegi... The 5 volts on a Bally pinball comes from the LM323 stabilizer how can draw max. 3amps..

First solution.

We just replace that with a LT1084 stabilizer who can draw 5 amps. The extra 2 amps is sufficient to run 5 extra display's. As there is some difference between the LM323 and the new LT1084 we have to pay some attention when mounting the LT1084.

De power board of a Bally ( = Stern ) The yellow arrows points to the LM323 mounted on his cooling strip.


Adaption is easy , here the datasheet of the LT1084 ...

Here side by side the LM323 ( left ) and the LT1084 ( right) .

We remove the LM323 from the board and fix the LT1084 using the UPPER bolt. At the back side we place a isolated washer that way the nut will not touch the run passing in that area. The LT1084 is mounted completely isolated.


We solder three short isolated wires and pass them trought the existing hole.

The numbers of the LT1084 correspond with the numbers here on the photograph. ATTENTION Some boards have engraved numbers do NOT follow the engraved numbering ONLY the numbers as on the Photograph!! Number 1 is ground and connected to pins 18,19,20,21 and 22 of connector J3.

Second solution.

Just replace the LM323 by a LM340K5 or 7805KC or 78H05KC that is a 5 volt regulator of exactly the same type and dimensions that can handle 5 amps... Cost a few $$ more..

Third solution.

Use an cheap extra 5 volts power source, such as an black feeding blok.Use one with a selectable output from 5 to 12 volts. Now by increasing the tension you will increase the brightness.

A good 1 Amp ( 1000 mAmp) power block, connect the - =0 volt at the ground and the + 5, 7,5 or 9 volts at the soldering point of former pin 1 at the display.

Another suggestion; When you have one failing display , put a LED display at the credits/ball emplacement, you can interchange Bally display at any location . ( player one to four) The little difference in color will almost not show on the credit/ball emplacement. Zaccaria has ALWAYS another coloring for the credits /balls display.. Another advantage is , when using only one LED display the adaption of the power board is not needed.