@GGG posted:It is one thing to say you can modify a read/write chip that is meant to be reprogrammed. And another to say you can change a read only write once chip under a blob of epoxy, so do tell how you would reprogram the board, even if not realistic or practical. Doesn't that really mean no not yes?
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Are you looking at a fire house circuit board and is there really a "blob-of-epoxy" (a.k.a. COB or chip-on-board)? Please post a photo for the greater good.
I was relying on the wiring diagram that GRJ posted earlier in the thread:
I do not see a COB component on the board - but a photo would tell all. I suppose the COB could be on the bottom of the board too.
But I am convinced this board uses re-programmable read/write digital memory to store the audio. The board is dated March 2015. If this was a design from the last century, then perhaps they used read-only technology. But today, an engineer who designs-in read-only memory for a product like this should consider another line of work. 
Again, a photo would tell-all, but circled on the diagram is a 28-pin SSOP chip next to an 8-pin SO chip. There are 3 pins labeled SCK, SO, SI. This suggests the 28-pin chip is a microcontroller and the 8-pin chip is a serial read/write flash memory, Serial ClocK, Serial Out, Serial In. To wit, I just checked DigiKey and a 4 Mb serial flash chip goes for less than 25 cents. As I recall, the initial PS2 engines only had twice that much memory and I figure a fire house is not as complicated audio-wise as an engine.
As stated previously, the heavy-lifting is reverse-engineering what is stored in the memory chip. Is it just two snippets of sound as GRJ observes...or is the sequencing of the lights/motors also stored? This would require test equipment that very few OGR readers have. And it would take much more time than adding an external sound board triggered by some light or motor signal coincident with when the audio is active.
