I acquired a Time Machine that has the DE sound board hum. I have recapped all of the boards, reflowed all of the header pins, replaced connectors and floated the sound board with nylon screws and washers. I tried running it with the displays unplugged (I realize this isn't a DMD machine, but I thought that I would give it a try). None of the work resulted in any noticeable reduction in the hum.

I couldn't stand the hum any longer so I did the PC power supply hack. I removed a power supply from an old Dell desktop machine and reworked it as follows:

* I removed all of the power and ground wires exiting the box by desoldering them from the board. I then resoldered one wire each for +5vdc, +12vdc, -12vdc and ground.

* A jumper was installed inside the power supply between ground and the "start wire" (PS_ON), which is the green wire in a Dell power supply. That allows the power supply to start as soon as AC power is turned on. It is normally connected to, and controlled by, the PC's motherboard. I'm not positive, but I think that is standard and ATX power supplies use the same colored wire. Be sure to confirm that by checking the schematic.

* I cut a 115vac power cord (to plug into the back of the power supply) and I routed the ground wire (green) into the metal box on the right side of the cabinet that has the fuse for the main power. I soldered the ground wire to the ground that came in from the wall cord.

* I cut the hot and neutral AC wires (black and white) on the pinball machine where they exit the on/off switch underneath the cabinet, and before the connector to the transformer, and soldered them back together along with the hot and neutral to the PC power supply cord. Heat shrink tubing was used to insulate the resulting connections.

* I put a fuse block with 5amp, fast blow fuses on each of the +5, +12 and -12 wires where the came out of the power supply. I then routed wires from the fuses, along with the ground wire, to a new connector that plugs into the sound board. The old power connector is laying next to the board and could be reattached at any time.

The power supply comes on seamlessly when the game is turned on (you wouldn't know anything had been added unless you look inside the machine) and there is zero hum coming from the speakers. I am OK with this hack as I did the work in a very neat manner and it has solved the problem with the damn humming. It is easily reversible if necessary as the factory power connection has not been removed.

Question: Did I place the fuses correctly in the power flow and what should their rating be?