These cars are equipped with factory-installed interior and end-marker lighting, which is DC and DCC compatible, but as mentioned in
https://www.therailwire.net/forum/index.php?topic=60817.0, the lighting is unrealistically bright. Rick sent me one of his cars to see if there is an easy way to get their brightness to a more realistic level. These are the instructions how to accomplish this with just two resistors and two trace cuts, and a small jumper.
VentureLightsSchematic.pngThis is a schematic diagram of the lighting circuit. With all the LEDs lit and 12.2V at the track, the unmodified circuits with red marker LEDs lit on both ends, only consumes 30mA of current (roughly 3.6mA per LED). As the modified diagram shows, two resistors were added. A single resistor in R2 location would have been sufficient, but it appears that when the 47 uF capacitor charges after brief loss of track connectivity it appears that some very sensitive DCC breakers (specifically DCC Specialities PSXX series) recognize that very brief current spike and activate their protection indicator. The current spike occurs when a discharged large-value capacitor is first connected to a source of voltage it appears as a short, with its internal resistance rapidly increasing as it gets charged. With a relatively small value of 47uF, the fully discharged condition is very brief, in microsecond range, but it appears to be long enough to trigger the DCC breaker. Adding a relatively low resistance R1 into the charging circuit will limit the initial charging current to where hopefully it will not trigger the DCC circuit breaker.
Since both resistors are connected in series with the original lighting circuit, they both affect the brightness. R1 has a very slight dimming effect, with R2 doing most of the dimming (by reducing the current supplied to the LEDs). Not installing R1 and using a 560 ohm resistor for R2 would have the same dimming effect as the circuit shown here with a 100 and 470 ohm resistors. This modification also dims the red EOT markers, which I think it also good, since they seemed too bright. Also, separating them would have greatly complicate the modification. The modified circuit only consumes 9.9mA in total.
LatchLocations.jpgTo take the shell off spread the sides of the car and pull out the floor/interior assembly. There are 8 latches (4 on each side). Either insert sharp toothpicks in the approximate latch location or use fingernails between the body side and the floor, starting on one end going towards the other end of the car.
Interior.jpgFor this modification I recommend fully removing the PC board from the car. Unsolder all seven wires, labeling their original locations. In this photo I did not label them. Couple of the wires for marker lights switch have color paint dots on them to make identification easier.
CloseupBottomView.jpgThis is a view of the unmodified PC board.
CloseupBottomView2.jpgThe copper traces on the PC board need to be cut in two places show here. I'll demonstrate two methods of accomplishing this.
One way I use is to use a hobby knife to cut through the copper trace. This cut is shown near the lower left of the B1 bridge rectifier. I like to actually make 2 cuts and remove a tiny sliver of the copper trace to eliminate any possibility of the separated trace reconnecting. To do this I repeatedly score the trace with a sharp hobby knife. But if you use a brand new #11 blade first break off the very end of the tip elsewhere, because if it is pristine, the point will break during cutting and embed itself in the PC board. Use a medium pressure pressure while scoring - do not press too hard. Make multiple passes until you can see that the cut is deep enough for the copper to separate. Repeat the process making the second cut. The sliver of copper between the cuts will likely just fall off, but if not,gently pick it out and remove it.
Second method uses a cutoff wheel in a rotary tool set for slowest speed, and gently "kiss" it to the copper trace that needs to be cut. This it shown near the top right of the B1 bridge rectifier.
DremelCutoffWheels.jpgI have use several diameters of cutoff wheels and pick the best one suited for the job. As I use the cutoff wheels they wear down and get smaller. I then save those for when I need them for tasks such as the one here, where a full size wheel would have made difficult to just grind into a small area like this.
CloseupBottomView3.jpgNext, the dark color solder mask needs to be scraped off the copper traces at the arrows. Using a hobby knife scrape the coating off. It is rather hard so multiple passes will be needed. Don't stop until all the coating is removed, exposing very bright bare copper, but don't scrape too hard not to damage the thin copper trace. If the copper appears dull then there is still thin layer of solder resist coating left and solder will not stick.
CloseupBottomView4.jpgAt this point install the resistors and a small jumper. Due to how small the circuit is I highly recommend using SMD resistors. SMD 1206 size is perfect for this. Begin with soldering one end of the "471" resistor to the pad for the B1 bridge rectifier. The jumper is a piece of 30AWG wire wrapping wire with its insulation stripped (still visible at the lower end of the wire). That wire is silver plated and solders very easily, which is important for miniature soldering. The extra length of wire is to make it easier to hold. I first stripped a length of insulation, then test fit it making a 90 degree bend. Then while holding it by the extra long piece I soldered it to the other end of the "471" resistor, and then to the exposed copper trace. Apply flux in every soldered location. It makes the solder flow much better and results in a good clean joint. This photo shows the flux still present around all the solder joints. Make sure to only use non-acidic flux made for electronic work. Acid would create problems later when it damages the delicate electronic components or creates shorts.
CloseupBottomView5.jpgAfter the solder hardens, place a hobby knife blade over the wire and rock it side to side slightly while applying the pressure to cut off the extra wire length. Then use 99 or 91% Isopropyl alcohol and a brush (toothbrush works well) to clean the flux off the board. Denatured alcohol should also work.
The angle of this photo makes it appear that the R2 is sitting over the copper trace near the top edge of the board. It is not, but even if it overlapped the covered trace the solder mask keeps it isolated from the trace.
That is it. Reinstall the board back into the car, and enjoy its more realistic illumination.
CloseupBottomView6.jpgThis image illustrates why choosing to use SMD components makes sense. The larger resistor is a typical 1/4W resistor, the smaller one is 1/8W and then there is SMD 1206 size resistor. Not only those resistors with leads are bulky, trying to bend and solder their wire leads will make this installation more cumbersome than using the SMD resistors which sit flat on the circuit board.
Power dissipation for the SMD resistor is not a problem here either. 1206 resistors are rated 0.25W, while in this circuit the 100 ohm resistor (at 12.2V track voltage) is only dissipating 0.01W and the 470 ohm is dissipating 0.05W or power.
I buy my SMD resistors at Digikey, for pennies each, but I'm sure they can also be found elsewhere like eBay, amazon, or direct from China. There are also inexpensive resistor kits available containing a range of standard resistor values. Be sure to get the 1206 size resistors as those seem to be large enough to easily deal with.
SOLDERING HINTS FOR SMD COMPONENTS
SolderSlivers.jpgBest way to make these small joints without needing a 3rd hand is to cut small slivers of solder, touch one with a clean soldering iron tip to deposit it onto the clean soldering iron tip (as it is shown on the tip on this photo), then apply this molten solder to the well fluxed joint area. The flux will allow the solder to spread and wet the solder joint. Using flux is very important for the cleanest and quickest solder joints, and it cannot be stressed enough times that a clean and shiny tinned tip is also very important for making good and quick solder joints. A wet sponge is the best way to keep the tip clean. Wipe it clean (removing any oxidation and extra solder) before each solder joint to be made.The solder shown in this photo is rosin core 0.030" diameter solder. Even though it has rosin, with the soldering technique we are using, that flux will burn off before solder is applied to the joint. Extra flux on the joint area itself is needed.
ADDITIONAL OBSERVATIONS
InteriorFloor.jpgThis car is also on the light side. The metal weight does not even extend the full length of the car (because of the switches in the floor). The car weights 1.22oz, and even the NMRA recommendation for this length of a car is 1.42oz. I would recommend adding even more weight (closer to 2.0oz) for improved electrical contact with the track. The weights could be concealed in the removable storage boxes under the floor or even in the vestibules.
VentureWhiteReflector.jpgI would also recommend that the bottom of the lighting bar be painted white or covered with white tape (as showing here). While it will not make a dramatic difference, the white surface will bounce some of the light creating more even illumination. Do not use silver paint as white does much better job than silver to evenly bounce the light back into the passenger compartment.
VentureLighting.jpgHere are some photos of the modified lighting taken at various ambient light levels, but since I only had a single car I could not take photo of before and after the modification.
As a side note, the circuit designers decided to add a small 1uF capacitor in parallel with every LED. While those capacitors are useful with front/rear headlights in DC-only locomotives to prevent flicker of the headlights, they are totally unnecessary in this circuit since the LEDs have their fixed polarity DC voltage supplied by the bridge rectifier. They could have saved themselves the cost of those capacitors and simplified the PC board design.
The need for this cap in DC locos is due to BEMF voltage the motor produces when the model briefly loses contact with the track (dirty wheels or other contact points in the loco). When that happens (usually for few milliseconds), the still spinning rotor of the motor briefly becomes a DC generator, generating a voltage in reverse polarity of the track voltage which was powering it. When the connectivity to the track is restored this effect stops. Back when DC locos had incandescent bulbs, the reverse voltage pulse was so brief, and with relatively low voltage this was unnoticeable, but with white LEDs being very efficient with very fast turn-in time, that brief reverse voltage pulse would cause the headlight in reverse direction to flicker. Adding a small capacitor in parallel with the LED basically shunts the voltage pulse, so it doesn't cause the LED to briefly flicker. But in this circuit there is no motor which can become a generator, and the large capacitor at the DC output of the bridge rectifier also smooth out very brief power drops, and the circuit is designed for the LEDs to stay lit regardless of the track polarity.
