Installed a Pinsound board in my GnR. First week was OK but than I started to get drops in sound when for instance pushing the flipper buttons. Measured voltage, was around 10.6 VDC. So barely at the mimum.

Changed BR, no difference.
Changed C4 (4x4700 uF) and now the voltage read like 10.95 VDC. Still far below 12 VDC but all is well again ( at least for a couple of games under loud volume)

Keeping fingers crossed

Had the problem again though much less severe. Only a few sound drops over a hour of play

Had some 10000 uF capacitors lying around so set three parallel over the existing 18000 uF capacitors making it a total of 48000 uF and hooked them up to the 12VDV test points. Played three very loud games and no sound drops

The AC input is by the way approx 19,5 VAC. After installing the extra capacitors the voltage went from 10.9VDC to 11.05VDC. The AC ripple from approx 0.35VAC to 0.25VAC.

Keep fingers crossed

I had replaced already the filter capacitors which reduced the hiccups but still some left. after adding the extra capacitors hiccups are 100% gone