Bally Space Invaders - some sounds incorrect - UPDATE

[gajaman]

Until recently I thought my Bally Space Invaders made all the right noises. Having watched this video on youtube I can now see this is not the case. Some of the game sounds seem to work ok but the trademark space invaders heartbeat and other sounds I can hear on the video are replaced by "pings" on my machine.

When you start a game you get a deep bassy sound but at this point the heartbeat thumping is replaced with a higher pitched "ping".

Also the blaster noise that should be there when a flipper is used is instead a simliar higher pitched noise. The sounds are not like interference or anything just like the wrong sound being played.

I have played with all of the dip switches on the MPU turning the various sounds on and off and this seems to work fine but I can't get the correct sounds.     

I've referred to my normal first port of call, the manuals at Pinrepair.com, but I can't seem to find anything that relates to some sounds playing correctly but others being replaced by the wrong sound.

Any advice to get all the sounds working correctly would be welcome.

My MPU is an Alltek replacement and the votage at all the test points of the sound module are as they should be.

 [youtube]http://www.youtube.com/watch?v=NstLPXusZ_0[/youtube] 

[gajaman]

Having fixed my dodgy solenoids by repinnning part of the MPU J4 connector it appears that things are much better on the sound front.

I have also noticed that the heartbeat thumping is there, it's just very quiet.

I have turned the volume on the sound board to full and all of the sounds are loud and clear except the heartbeat that is there but faint.

I have hooked up a second speaker in case the installed speaker can't handle deeper sounds or something but the second speaker (which isn't very good, it's been kicking around my garage since I took it out one of our cars a number of years ago) sounded exactly the same.

I connected the second speaker by soldering car speaker wire to the connectors on the cabinet speaker and then attaching the second speaker with quick connects.

Should I try a new better quality speaker or is there something else that would make this one sound faint and all the others loud and clear? It's been a long time since I messed around with car stereos but I remember using a cross over to filter out deep sounds to prevent ruining tweeters, could there been a filter somewhere that could cause this on my machine or am I way off target?

[Ken Layton]

Has the sound board been recapped yet?

[gajaman]

I haven't done anything to the soundboard at all, what do you mean by recap?

[qrz]

I haven't done anything to the soundboard at all, what do you mean by recap?

replace electrolytic capacitors.

'lytics tend to change value/develope high esr/ LEAK 

and they are a common failure in MOST electronic devices   

[gajaman]

Thanks qrz.

According to the sound module part list there are like 22 capacitors on the board 3 of which are pretty large. Would you advise changing all of them or starting with ones that are most prone to failure?