N Scale Kato F7

This page is no longer under construction. It's as good as it's going to get.

The Kato F7 is an example of a great looking and running N scale locomotive that is not "DCC ready" out of the box. This is due mainly to that fact that the frame completely fills the shell, leaving no room for the decoder. The good news is that the F7 is one of over 40 N scale locomotives that Aztec Manufacturing supports with their Track Master frame machining service. If you want to learn more about Aztec and their products, click here.

Recently we had a pair of these locos in the shop for DCC conversion using the new Lenz LE0511W decoder. I stripped down the frames and had them machined by Aztec. As I was sizing up the install after receiving the frames back from Aztec, I noticed that the shell had two headlight lenses while the frame only accomodated a single LED behind the upper headlight. The LED mounts on a small circuit board that fits between the frames halves, and the clear plastic headlight lenses are actually a single piece with a light pipe connecting them. While this arrangement does manage to get some light down to the lower headlight, it wasn't nearly as bright as the upper light. Besides I wanted to employ the lighting special effects available on the LE0511W to simulate a Gyralight on the upper headlight, and that required that the upper and lower lights operate independently.

I contacted John Claudino of Aztec, and asked if he'd consider supporting the lower headlight in his program for the Kato F7. I explained how I would like to use a surface mount LED to directly illuminate the lower headlight lens, and emailed him a sketch of the required change and an outline drawing of the LED. John was very enthusiastic about the change, and asked me to return the two frames so he could work out the changes to the program.

When the frames came back from John they were perfect, as you can see below. The LED fit right in behind the lower headlight lens with plenty of room for the wiring.

Next I got to work on modifications to the light board to allow it to support the second LED circuit, as well as to supply track power to the decoder. The first step is to remove the resistor and yellow LED with a soldering iron, being careful not to lift the copper traces from the board. After the components are removed, the board should look like this. The sketch shows the circuit side (bottom) of the light board. The three main copper traces on the board are shown as light areas on the sketch, while the dark areas are bare board between the traces.

The next step is to remove several areas of copper from the board. This is easy to do but does require some care as the board is thin and small. Simply cut through the traces on the edges of the areas marked in red on the sketch, using a sharp blade and your favorite hobby knife. It is better to press lightly and make several passes with the blade to cut the trace. If you press too hard you could possibly cut through the board or have the knife slip and cut a trace you didn't want cut. After cutting the traces as shown, use the tip of the blade to lift the copper parts marked in red from the board.

I installed two surface mount resistors (620 Ohm 1/8 Watt 1206 size -- Digi-Key part number 311-620ECT-ND) as shown by the green rectangles in the sketch. A good pair of tweezers, a soldering iron with a fine tip and a steady hand are needed to do this successfully. It is helpful to tin the ends of the resistors before soldering them to the board.

Next I installed the upper white LED (T-1 size -- Digi-Key part number 67-1606-ND or CMD204UWC-ND) and connect the wires. Too much heat applied to the small pads may cause them to delaminate from the board, so be careful when soldering.

Add the lower white LED (3.2mm x 2.8mm surface mount -- Digi-Key part number 67-1608-1-ND or CMD67-21UWCCT-ND) stuff.

Put it together and test it. Program the CVs so that it works like a gyrolight. Have fun.

Follow the link for images of the install and operating headlights.

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Copyright 2003, 2009 by Robert M. Luzenski, all rights reserved