@gunrunnerjohn posted:
Pretty sure it's not a COB, here's a picture of the actual board I got from this thread.
...
Well that seals the deal! The 28-pin chip is the MSP430G2403 microcontroller (less than $1) which doesn't have enough memory for audio. Hence the companion reprogrammable read/write flash chip. That the board has evenly spaced pads for SO-SCK-SI suggests this might be how the manufacturer programs (or re-programs) the sound memory chip in-situ. The days of popping out and replacing a memory chip to change sounds is so last century! 
@gunrunnerjohn posted:...
I think it would make adding the sounds fairly easy, the hard part is actually coming up with realistic sounds for the sound clips.
I think the OP could cut-paste some clips from the movie. And perhaps using Audacity or similar "free" audio editor can mix in some additional mechanical-sounding effects.
I dug up this video of a fire truck I made in 2003. It uses the microcontroller plus read/write flash memory combo. The sound was spliced together from various audio clips off the web. It can take hours and hours to scour the web to find a snippet of clear audio that doesn't have music or whatever in the background.
Plus, based on the linked OGR thread on distortion in the fire house audio amplifier electronics, I don't think modifying the existing memory is worth any further study. If you do go with an MP3-based sound board with integrated audio amp (as shown in an earlier post), the audio quality will be vastly superior to what I heard from the online videos of the fire house.
