HST 125 unit ditch and tail lights

You back already. The device in the picture is what is needed for the power units. Basically it consists of a piece of a LED lighting strip cut from the extra ones I bought. After trial and tribulation I found out that these things appear to be connected in sets of three LEDs in series with a resistor. You will notice that there is a scissor mark in the middle of the unit. I choose this section because I know that the two LEDs are not connected to each other. Therefore they can be treated as discrete units. Take a closer look at the unit. Clicking on the picture will give you a close up view. Notice the positive rail marked (+) is closest. The 1000 Ohm resistor has one lead connected to both white LEDs at the anodes. It is then trimmed off. The lead on the top is bent over and cut short. I used the remainder of this pig-tail to connect the two cathodes together. This forms the basics of the circuit. The tail lights are connected directly to the wire joining the two anodes of the white LEDs. Another piece of tinned copper wire was obtained from the rubbish before it got to the bin. It was also a cut off pig-tail. This was soldered between the two cathodes of the red LEDs.

How did it all get there? Read on. First I tinned one leg of the 1k resistor. Soldered it between the two white LEDs at the anodes. Then I bent the resistor leads into the shape you see and trimmed off the excess from both the furthest LED and the opposite end of the resistor. The longest pig-tail removed was long enough to use as the connection between the two cathodes of the white LEDs. Note the small extension past one end. It is to facilitate connection of the white wire. Next using super glue applied to the base of one the gull-wing LEDs stick it in place on the surface of the unit up against the anode wire with its black line closest to you. Do the same with the other gull-wing LED.

Using a flux pen wipe flux over the two places where the gull-wing LEDs touch the wire. Then solder these. Be careful while doing this. These devices won’t take much heat. Place another piece of pig-tail under the other two gull-wings. It should fit pretty slug. Using the flux pen apply flux to these joints and solder them in the same fashion. Note the length of this pig-tail. It should have a bit of an extension for the yellow wire. Once this is done solder the coloured wires on as per photograph.

Now we need to test the device before sticking it to the power unit. With a 15 volt power supply connect the blue wire to the (+) positive of the power supply. If everything is all right the white wire touched to the (-) negative terminal should light the white lights. Doing the same with the yellow wire should light the red lights. To the loco or power unit as they are called.

Remove the body of the unit. At the front remove the bulb and its wiring. This article assumes that you have already converted the unit to DCC. Behind the bulb there is a black plastic panel. The unit should be trimmed to fit this. Make sure that there is no oil, dust or dirt on the plastic panel. Test fit the device we created on to the panel. Once you are satisfied with the fit take the cover strip from the back of the device and stick it in place. The white LEDs should be at the top and the red ones at the bottom of the power unit. The wires will be to your left as you look at the front of the unit. You shouldn’t have any trouble working out where to connect the wires. After all they are colour coded the same as the DCC chip’s wires.

Place the power unit on a short piece of track. Connect up your DCC controller to the track. Select your power unit. Switch on the head light. If you are in forward gear the white lights should light up. Change to reverse. The lights will change to red. Put the body back on the unit. You are done. Note you may have to advance the throttle a little to get the chip to change direction. There is one more unit to do. I choose to use a second chip in the rear unit to operate the lights on the rear. It does seem to be a bit of a waste though. There is a little trick to remember when wiring the rear unit. Connect the white wire to the yellow one and vice versa otherwise you will have white at both ends in forward and both ends red in reverse. The Hornby “Select” controler doesn’t like two chips with the same address on the layout. It will complain.

Tools used on two projects shown in photo bellow. There are three items missing from the photo. They are a white out pen, a pair of scissors and a roll of electrical insulation tape.