All, first happy to now be a part of the forum and back into the hobby. Yesterday I picked up an MTH fire station 30-9102 from my local dealer and brought it home and was very sad about 2 things, the truck motor to move the fire truck in and out did not work at all and the sound was terrible from the sound module. The motor was an easy fix, bad solder joints on the wiring at the motor, but the sound I did a little reverse engineering on the MTH mainboard and figured out a massive and relatively easy fix for those with this station. This makes a dramatic night and day difference to the sound quality.
The issue is, the sound signal source trace and circuit from the microcontroller has 2 capacitors shunting and distorting the signal to the amplifier before it's even amplified, meaning the amp just takes this now distorted signal and makes it even that much worse. The fix is amazingly simple, remove these 2 surface mount capacitors and enjoy instantly better sound. I'm really struggling why the designer put them there in the first place. I mean I understand filtering, and stray voltage protection (any capacitor to ground on a signal circuit basically shunts high frequency or voltage transients to ground)- however, in an audio circuit, let alone the signal feed into the amp, this was a bad thing.
Anyway, all you need is any soldering iron to just heat both sides of the tiny surface mount cap and since we are removing it, most irons have a long enough tip to touch both ends and then just slide it to the side off the pads and that's it.
A picture says 1k words- so here is my first diagram and post.