Ok, It may be that the BR1 bridge rectifier on the power supply board is checking out or maybe something is amiss on that board,TA-100. These are often hacked up and re-worked by now, or maybe replaced with a new board? I see reaper802 beat me to the punch lol.
But the static is making me wonder about the sound board SB-300.
The easiest thing to do now is verify that the Alltek lamp driver has been installed correctly. I couldn't find the complete manual for it online but this is a start:
https://cdn.shopify.com/s/files/1/0071/0810/0141/files/Lamp_Driver_Manual_A_6.pdf?132 but this is missing the last page (6) with the Stern speech game instruction for some reason.
You may even have the manual for it? If so that's great. First verify that the jumper from Alltek J13 was installed and wired into the feature lamp bus line and not the GI bus line, easily confused between the two. Then go to Alltek J4 connector wires going to the top connector of the speech board(VSU-100).
You should see that the wires between J4 lamp driver to the speech board have been cut or removed. You will also see on the left side of the Alltek J4 header pins 9 and 10 marked :SW Illu bus voltage. If there is still a connection there, it could have damaged the switch ill. power supply.
If all that is good, go back to the sound board and pull the connector J2 and see if you still get the brown out.