Midway SI sound problem - saucers

[gridrunner]

Hi everyone,

I'm just fixing a Midway SI board that has a missing saucer sound. The distinctive warble is only a mild hiss. The schematics and YouTube tell me that the SN76477 sound generator is down, so here's a retro part in an attempt to fix a retro part. We'll see if it works!

Anyone remember individual LEDs being sold in blisters with the Archer brand in branches of Tandy in the 80s

 

[duncthepunk]

the sounds was generated by single chips in a row lm3900n chips work on moonbase .the board is base on tatio space invaders board set . if you downloas the shcematics you see that each bleep and bang noise was made by 1 chip . the hiss is will be cap related to a point . but if the amp is damaged .(the one with heat sink ) that will need replacing . I could be wrong bally midway might have done this differently (download the schematics .best of luck

 

[gridrunner]

Hi there, thanks for the feedback. I'll post more detail as a fix log, but changing the Op Amp at K4 fixed the missing saucer explosion and replacing the sound generator SN76477N fixed the missing saucer flying sound. From looking at the schematics it looks as though the saucer 'warble' is all that this chip is called upon to do, but it was quite hard to find one. The one I had hadn't been out of its packet for almost 40 years but moisture had crept in and corroded the pins. Luckily a bit of sanding fixed this and the chip seems to work just fine. Thanks Tandy!