I have been using a universal module in the momentary mode to turn on one of my computers for over a year. It worked OK except for the loud "thunk" every time it was energized. I never have like this loud sound and started looking for a better way. As it turns out, the mod, even with the extra parts, is still quite a bit less expensive than the universal module.

I looked at the plain ol' Appliance Module to see what I could do with it and came up with the following mod.

The result is a momentary relay contact switch that will close a relay contact for approximately 2 seconds when energized.

The parts list.....

• 12v 1w zener diode - 1N4742
• 220 mfd. 35v electrolytic capacitor
• 470 ohm 1/2 watt resistor
• 12 volt reed relay - All Electronics part # - RLY-407
• 2 screw terminal strip - All Electronics part # TER-200
• 2 #6 1/2inch sheet metal screws

All parts except for the screws are availible from All Electronics www.allelectronics.com

A word about the relay. This is a somewhat special relay because of the very high coil resistance - 4650 ohms. This results in a coil pull-in current of only 2.5 ma. This allows me to use the small 220 mfd cap to filter the output of the SCR. If you want to use another relay, the cap value will probably have to be changed as well as the 470 ohm resistor. The relay specified is just about perfect for this application and I highly recommend using it.

To use the modified module, just send an "on" command to it. It will close the relay contacts for about 2 seconds.

Disclaimer
This article documents modifications to the X-10 AM-486 Appliance Module. Opening this module will void your warranty. And more importantly, removing this module from its case will expose you to the possibility of electrocution. This module connects DIRECTLY to the line voltage (120 Volts). When is out of it's protective plastic cases, it can kill you if connected to the wall socket and you touch the wrong thing. Do NOT connect this module to the wall while removed from the case! Be very careful! Also, there is a possibility of the module catching fire if wired incorrectly and plugged in. Proceed at you own Risk! I take no responsibility if you electrocute yourself or cause a fire.

I used 24 gage hook-up wire for this project, unless otherwise indicated. I found that anything bigger would not fit in the smaller holes in the PC board. The actual wire is from some scrap CAT5 ethernet cable. To connect the relay terminals to the terminal block, 24, 26, or 28 stranded wire or #28 or #30 solid wire is highly recommended.

Remove the 2 phillips screws from the Appliance module unit.

Holding the unit with the dial down, lift up the end with the prongs using the prongs. This will lift the upper case and the circuit board together. After you lift it up enough, the other end will seperate from the bottom case.

Put the part with the dials in a safe place so that you will not bump it and disturb the dials. They can be a little difficult to get back in. Remove the circuit board from the rear part of the case.

Here is the circuit board as it comes from the factory
Now remove the relay. The relay has 2 small white wires, a larger black wire, and a tab that goes through the circuit board. You might have to pry up the tab with a small screwdriver while heating the pad underneath. The board now looks like this
We will be using the 2 holes that the white wires were connected to
We are going to hotmelt glue the relay to the PC board. The glue does not stick very well to the slick surface of the board. Use a small piece of medium sandpaper to remove the gloss right above the 2 large holes.. Also use the sandpaper to remove the gloss on the side of the relay. Looks like this:
Go ahead and hot-melt glue the relay to the circuit board. Position as in the photo. Make sure that the top of the relay does not overlap the edge of the board. Also make sure that the relay is not any further to the right than shown in the photo. Actually the optimum placement of the relay is about 1/8 in to the left of the location in the photo. The relay contacts should be parallel to the circuit board.
Bend the leads of the 12V zener diode and solder to the relay coil contacts (the 2 center ones). Be sure and position the end with the band to the right as shown.
Now install the 220mfd capacitor to the zener diode as show below. Be sure and solder the + end of the capacitor to the side with the band. Also make sure that there is at least 1/8 of an inch of space between the end of the cap and the AC pin. There is a plastic piece in the case that will have to fit between the capacitor and the AC pin.
Now install a 470 ohm 1/2 watt resistor from the zener diode (band side) to the hole shown in the photos below. The end of the resistor that goes to the hole will probably touch the AC pin and the capacitor near it. This is OK. The AC pin and the capacitor are already both connected to the hole. Install a wire between the other side of the zener diode and the hole shown on the photo. I used the 24 solid wire here but it just as well could be the same stranded wire that is recommended for the relay contacts described later.
Time to modify the case so that we can mount the terminal strip. Place the terminal strip on the case and mark the places with the slots. Its location is show in the photo below. Then cut 2 slots for the pins that will connect to the relay. I used a small hand saw to make these. Then place the terminal block into the slots, line it up, and make a mark where the mounting holes are to be drilled. Then drill the holes with a 3/32 or 7/64 drill bit. The second photo shows the terminal block temporarily mounted to give you a better idea of the location on the case. If you mount the terminal block to check the fit, remove it for the next step.
The only wiring left is the run a wire from each end of the relay terminals to the terrminal block. A note here. The relay connections are very thin and brittle. They can't take very much flexing before they will break off. I did break one of the relay terminals during the first attempt doing this mod. The problem was that the original wire that I used was too stiff and it flexed the relay terminals too much when I re-installed the circuit board. It is recommended that you use very small solid wire(#28 or #30) or use stranded wire no larger than #24. You want flexible wire so that when you mount the terminal block and the circuit board, the wire will flex easily. Although it does show well in the photo, I did bend the relay terminal next to the capacitor up so that it would clear the cap and make it easier to solder the wire to it.
Place the board and the terminal block back into the modified case. The terminal block should slide right down into the slots. Secure it with the #6 1/2 sheet metal screws. Pick up the front of the case (the one with the dials) and place the other part of the case(with the circuit board & terminal block) onto it. The bottom of the case should be inserted and lined up and then you can swing the top part down so that the case fits together. This takes a little practice.