Repair Bally sound card type 2815-32.

This board is the most simple you can find on Bally pinball machines.

You do need some specific material to repair it outside of the pinball machine. This includes a speaker, 5 and 12 volt power supply , an electronic probe (DIY model can be found on this site) and a pulse generetor. The speaker can be anything, 8ohm is best but 5 to 16 ohm will also work. I use a little car speaker. You can also use the speaker from the pinball machine. The 5 and 12 volt you can get from a power supply of a computer. The electronic probe is needed to follow the signals through the different chips. The pulse generator I have designed is very simple and only consists of 6 parts. You'll be able to use this for other repairs I'll explain in the future on my site.

This is how the sound board 2815-32 looks like.

What you need for the pulse generator:

An IC type 4011 with socket, 2 resistors:2,2 Mohm and 100Kohm, a condo of 100nF and some board of 3 on 2 centimeters. And some wire and hooks.

These are the schematics.

The finished pulse generator.



The sound card normally works with 5 and 43 volts. However the 43 volts is brought back to 12 volt on the board itself. Because 43 volt isn't easy available, we work directly with 12 volt. Should your card work fine on the testbench but not inside the pinball machine, you'll have to check if you have 12 volt on TP3 and 43 volt on TP4. If you have 43 volt but no 12 volt then it's Q1 which is responsible and you have to replace this..

Connect the sound board like this: The speaker at the two pins bottom connector, +5 volt on pin 5 and ground on pin 6 of connector J1. Connect +12 volt to TP3 and the ground of this 12 volt also to the pin 6 of connector J1. The output of the pulse generator goes to pin 8 of the connector. The power for the pulse generator can be take from TP1 for +5volt and of TP2 for ground.

If your sound card is ok, you'll hear a sound from the speaker. The height of this sound will change if you connect pins 1, 2, 3, 4 of 12 of the connector to ground. You can hear this sound here: and in the middle of the sample you'll hear a change of tone, which is what happens if you i.e. connect pin 12 to ground...

No sound.

First check the parts which amplify the sound, these are U10, U9 and U8. We inject a humming sound using a screw driver of which we touch the side with our finger, against some IC pins. Do this on these parts: pin 2 of U10. If you don't hear any sound then replace U10. If OK then touch pin 2 of U9, if you don't hear anything, replace U9. Pin 3 of U8, a softer but noticeable humming sound, if not, replace U8.


If the amplifier seems ok then we check the dividers. The pulses we introduce on pin 8 of J1 drives Q2 which drivers timer U7, his output is a flow of impulses. We check at collector of Q2 if pulses leave, and on pin 3 of U7 if pulses arrive, using the electronic probe. This flow of pulses will now drive divider U2, and U2 drives U3, then U4 and U11. If these dividers work well you'l get a different tone when you put pins 1, 2, 3, 4 or pin 12 to ground. If this is ok, the sound board is working completely. If the sound does not change or there's no sound at all, check with the probe if you get signals on the pins of U2, U3, U4, U5 and U11.

We measure ok at the collector of Q2, if input of U7 has no pulses = replace Q2. We measure ok at the input of U7 but not at the output of U7 (pin 3) repllace U7. Of course don't forget to check if there is 12 volt on pin 4 and 8 of U7.

Measure this on the dividers (check with the probe if you have pulses)

U1 / Pulses on pin 4, if not replace U1.

U2 / Pulses on pins 3, 9, 12, 15; pin 16 = 5volt

U3 / Pulses on pins 1, 2, 3, 4, 5, 6, 9, 10, 11, 12, 13; pin 16 = 5 volt.

U4 / Pulses on 1, 2, 3, 5, 6, 7, 9, 11, 12, 13, 14, 15; pin 16 = 5 volt.

U5 / Pulses on 3, 5, 6, 7, 9, 11, 12, 14, 15; pin 16 = 5 volt.

EXTRA U5 Pulses on pin 2 , if you connect pin 12 of the connector to ground.

U11 / Pulses on 1, 9, 11.

If one of these pins does not show pulses, use the schematics to see if it's an output of U2, these go through U1 before entering U3. By these gates you can make a difference between the input of the next chip and the output of the preceding one; for the other parts this isn't possible. Output pin 3 of U3 is connected to input pin 11 of U5, and there are more like this, so you will have to cut the connection to make sure if it's the output that's missing. If the connection is broken and you have an output signal, then it's the chip where the signal enters which is broken ! So you'll need to search a bit until you can be sure whether the output or the next connected input causes the missing pulses.

Once you've searched the whole board and repaired the problems, you'll hear sounds from the speaker ! Good luck !

Back to home-page ....