Konami Time Pilot noise

I have a Konami Time Pilot (at least that's what the screen says).
The cpu board has about six daughter boards, instead of the custom chips.

The problem is a nasty buzz on the audio output.
It appears to be being picked up from the main CPU board, the track between the LA4460 power amp and the volume control acting as an aerial.
If I attach a 1000uF capacitor to the CPU board, I reduce the buzz by about one third.
If I cut the track going into the power amp at the amplifier, it kills the nois completely.
If I cut the track at the volume control, the buzz persists.
The volume control adjusts the game sounds, but has no effect on the buzz.
I've cahnged the LA4460, to no avail.
Behaviour is the same on a bench PSU.

Any ideas as to how to deal with this one?

Mark

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Received on Fri Mar 17 16:29:33 2006