Step 11 : Circuit Modification Option 1


The easiest change is to simply remove the 100uF capacitor and replace with a 1000uF, 10v one. It will fit inside the case if you leave longer leads and lie it down. Two possible problems. The first obviously is that it may not maintain power to the IC for the required 20 hours. The second is that it delays the initial turn-on of the lights while the cap charges. It can delay it by up to 30 seconds or more. Gives you a fright the first time because you think the lights have stopped working. But just be patient. If you leave the lights on all evening once turned on, who cares. If they are part of a computer controlled sequence it is no good.

If the turn-on delay is not a problem but the capacitor doesn't last the required 20 hours, it may because some of the power is draining out via the dropping resistor and light string. To avoid that, unsolder one end of the dropping resistor and solder in a small diode. The cathode (with the line) faces towards the IC. (It all depends on whether the small charge the capacitor supplies to the IC is sufficient to turn on the SCR's, which it normally isn't, or whether the SCR's are "leaking" at all, or if your circuit design is different. Normally the diode is not necessary.)

You cannot use a 1F cap with this option. It delays the turn-on for much too long.

Step 12 : Diode on Dropping Resistor


Photo of diode inserted in series with the dropping resistor, as in option 1b.

Step 13 : Circuit Modification Option 2


Solder a 1F, 5v memory backup capacitor in parallel with the 100uF cap, with a 5.6k resistor on one lead. The cap is flat and is small enough to fit inside the case. The negative lead can go to any negative rail on the board. Use a short length of insulated wire to connect it. The positive lead goes to a 5.6k resistor then to the positive of the 100uF cap (which is also the +ve pin of the IC.) The resistor stops the 1F cap stealing all the power at start-up and thus avoids the turn-on delay. You may need to vary the resistor up or down in value. Wrap the cap and resistor in some duct tape to insulate it from the rest of the board. You can also insert the diode as in option 1 to stop power being lost via the lights if necessary.

I have been running about 20 sets with this option for 3 seasons now with no problems. All but one use the diode option. The first time I turn them on for the season I have to select the required function. After that they remember. (I had one this year that had remembered for 9 months and didn't need to be re-set!)

Step 14 : Circuit Modification Option 3


This is a cheap and nasty solution but it works fine. Buy a single AA battery holder. The little plastic ones with two wires attached. Solder the black wire to any negative point on the board. eg. the negative of the 100uF cap. Solder a diode to the red wire, with the cathode (line) furthest from the battery holder. Solder the cathode end of the diode to the +ve side of the 100uF cap (+ve pin on the IC). The battery holder will not fit inside the case so you have to route the wires outside the case and tape it on the outside. Install a 1.5v battery at the start of the season and remove it at the end. It will last the season and longer.

Step 15 : Circuit Modification Option 4

Neater then option 3 but a nuisance. Get a 3v lithium memory backup battery and install as for option 3. Advantage is it fits inside the case. It will last for ages but when it does eventually run flat you have to open the case, unsolder it and install a new one. This option is ok if you happen to have some spare lithium batteries lying around but if you need to buy them then option 2 is better.