Micro Ace AE100形 “Skyliner” DCC Pt 1: Cab Car

A Keisei AE100形, headlights blazing.

Ok, yeah. I said my next DCC conquest would be my Kato 651系 “Super Hitachi”. I lied. Besides, I said that, what, six months ago? I don’t have the necessary decoders on hand to continue work on it, but I did have the necessary decoder for this model, the Micro Ace A2896 Keisei AE100形 “Skyliner”.

What makes this model challenging is that the headlights and the markerlights are not lit by distinct LEDs, but by a single bi-polar bi-color LED—a single monolithic LED that cannot be split apart into two distinct circuits for control by two distinct motor leads. Read on to see how I got it working.

A monolithic bipolar, bicolor LED. The gray circle represents the monolithicity of the component. The red squiggle represents the tears of my ancestors.

The problem with this model is that the prototype’s headlights and markerlights use the same lens; in the model, this means that the LEDs will share a common lightpipe. And the easiest way to do that is to use one bi-polar bi-color LED. The schematic shows what this looks like: It’s equivalent to two LEDs put together back to back (as it were), but packaged together into a single two-lead package. The red LED comes on when current flows from right to left; the yellow LED comes on when current flows from left to right (assuming conventional current, rather than electron current). A very tidy solution for DC running—but a very bad one for DCC conversion.

I circumvented this difficulty by using a motor decoder. The basic strategy is to isolate the circuit board, and wire the motor outputs to the inputs on the circuit board. This way, you can control the lights with only two wires, using the throttle. But, as with DC running, the brightness will depend on the throttle position, and when the throttle is at neutral, the lights will go out. That’s no good!

So, for this project, I selected a TCS decoder. Recent TCS decoders have a feature called “button control of the motor”, which allows you to control the motor via function buttons instead of the throttle. The idea is quite brilliant. On one hand, you can use a simplified throttle for shunting operations, where fine speed control is not called for. On the other, you can use the motor leads as auxiliary function leads to permit control via the function buttons of high-current devices such as smoke machines, or other bi-polar devices, as I did with the lighting.

Because I wanted to hide the decoder, and because space was tight in the cab, I chose to use a Z2 (the very one I had lying around awaiting a purpose). Now, I know Arthur from TCS (hello! if you’re reading this) told me not to use Z2s for N scale models, but I figured that this application couldn’t hurt. The LEDs draw no more than 40mA (there is a second LED I didn’t mention above): There’s no way I could tax this decoder beyond its capabilities. Right?

There is one caveat with such an install: you must disable any back-EMF control before you put it on the operating track! The motor output is designed assuming that it will be powering an inductive load, like a motor. Most modern decoders, including all of TCSs products, take advantage of a unique feature of inductive loads to improve performance: A motor, when turning under momentum, generates current (called back EMF), it becomes a dynamo. The decoder can cut off power to the motor, measure this current, and adjust the amount of current going to the motor to maintain a constant speed, despite irregularities in the track or gradients or changes in load. A very nice feature, except LEDs are not an inductive load: They don’t generate any current when idling! So they risk confusing the feedback feature—I don’t know how TCS implemented this feature on their decoders, but I’m not going to risk dead LEDs. So turn it off, and the “dither” feature too (because I’m not sure what “dither” does, and I don’t want, as I said, dead LEDs). To turn these features off, set CV61 = 0 (Back EMF off; but notice that this CV also turns on button control of the motor; see below), and CV56 and CV57 = 0 (dither off).

Disassembly

The cab car—in parts. Don't lose those tiny screws!

On with the install. Pulling the shell off is no different than for any other Japanese model: Pry the sides outwards, and pull the bottom frame downwards. The skirt at the diaphragm is attached to the shell, and likes to get hung up, so be careful with it. The shell of this motor is curiously thick. Unscrew the trucks. Unscrew the switch installed just behind the cab (careful not to strip the screws!). Lift the seats from the underframe, being careful not to lose the lightpipe and control rod seated between the two. (Indeed, be sure to take note of how they are seated! The control rod connects the electric switch to the light pipe, which moves in and out.) Gently (but firmly) pull straight out the blue divider between the cab and the switch you just unscrewed. Unsnap the black cowl in the cab area.

The circuit board is held in place by this retaining clip.

Inside of the cowling is a circuit board. The board is held in place by a small retaining clip. Both the cowl and the clip are black, making the clip perhaps a little difficult to see. The clip is held in place by the springy force of the two prongs: Remove it by pulling out one prong, then the other. The circuit board should just fall out after that.

Z2 Installation

Solder the red and black leads to the metal rails. But not like I did, solder them as indicated in the text and in the photos below.

Now, trim the red and black leads on the decoder down a bit, and solder them to the rails. I recommend holding the rails in a hobby vice: They will get quite hot as you solder! I also recommend a temperature-controlled soldering iron for this bit of work. It took quite an effort to get the rails hot enough to wet with solder. However, I found that the best way to orient the wires is the opposite what’s pictured (didn’t photograph the improved results). Rather than have the wires lead outwards from the rails, as pictured, you should have the wires lead inwards towards the rails. This will relieve a lot of stress on the solder joint, as you will see.

You will have to carve a pair of notches into the cowl to accommodate the pickup leads.

You will have to carve a couple of notches into the cowl to accommodate the pickup leads. A little trial and error goes a long way here: Try assembling the underframe to get a sense of the best location and shape of the notches. Don’t forget that you will need to notch the retaining clip too (gently! don’t cut it apart!).

Decoder in place, ready for first test.

At this point, before you solder up the circuit board, you must test and program the decoder. Assemble the underframe and trucks, and test-fit the decoder. Place the decoder on the programming track, and attempt to read the decoder’s address. If you get back a 03, great. Now is the time to program the decoder to deactive Back-EMF and dither (see above): Program CV56, CV57, and CV61 all to 0. Take the model back apart.

Detail of the circuit board, highlighting the two contact springs. We will be removing those springs.

The circuit board gets juice via two springs that press against the metal rails in the underframe. We will replace them with wire leads from the decoder. So, desolder the wire springs, being careful to soak up all the excess solder to leave a nice, clean hole to thread the decoder’s motor leads through.

The decoder soldered to the rails and the circuit board. Notice that the motor leads are threaded through the cowl. Notice also the corrected orientation of the pickup leads on the rails.

The cowl has a convenient hole in the top (not sure why it’s there) through which we will thread the decoder’s orange and gray motor leads (you should have trimmed off the white, yellow, and blue leads from the decoder). Trim and tin the orange and gray motor leads, then thread them through the top of the cowl. Thread the two leads into the holes left by the springs—you should thread from the side without LEDs through to the side with the LEDs. Solder the leads into place on the LED side of the circuit board and trim off any excess. Notice in the photo the correct orientation of the pickup leads on the metal rails.

Reassemble the underframe and trucks, and test it out! Tuck the decoder between the cowl and the blue separator as in the photo above, tucking the leads in neatly around it. It should just fit. Try to read the decoder address on the programming track. If that succeeds, and only if that succeeds, take it to the operating track.

On the operating track, you should find that the lights will brighten with increased throttle, and that reversing the throttle will change between headlights and markerlights. If you wired it up like mine, you will find that the directionality is wrong: Markerlights come on at “forward” and headlights at “reverse”. Just alter the normal direction of travel in CV29 to fix it.

Button control of the throttle is activated by setting CV61 to 68. By default, the motor circuit is activated by F2; on my throttle, F2 is momentary, and doesn’t actually work with this function. Set button control of the throttle to use F3 by setting CV134 to 16. Now, you should be able to turn the lights on and off with F3, and alternate between headlights and markerlights with the directional control, regardless of the throttle setting.

Repeat with the second cab car.

Read on to see how I converted the motorized car of this model.