Zmodell digital decoders for Märklin US passenger train sets

Greetings to all,

During the first lockdown in this spring, I got more time to devote to my hobby. In that period, I had an opportunity to develop a number of digital interior lighting boards even for some “forgotten” and “abandoned long ago” train sets. Among such articles, there are American passenger train sets from Märklin. They developed them long ago, in the beginning of 80’s, when there were no competitors in Z scale at all. I think their American Z scale models looked great and innovative in that period, but then AZL and MTL entered the market and actually ousted Märklin’s Z scale models out of the playfield.

Single unique models from Märklin like Bumblebee and Commodore Vanderbilt do not play any major role in this battle, as they have much more collectible value than a mainstream rolling material.

2020’s Märklin’s effort to refresh their American Z scale portfolio by producing three articles – two locomotives and one freight car set is not bad in general, but it is quite strange to me, because all cars in this set are the same well-known outdated models, and new lettering and packaging will barely “save” them. And selling already well known, entry-market, very basic AZL locomotive for 210 Euro, while AZL sells it for only 100 USD, is also questionable to me. But surely it is a subject of a different discussion.

Some years ago, I got a chance to buy these old passenger train sets for bargain prices on eBay. Surely, these models are incomparable with modern coaches from AZL, they are simplified in many points and less detailed, and even slightly out of scale, but there is still some room to convert them into a bit more attractive thing.

Here is a list of these train sets:

87845 – Baltimore & Ohio streamliner car set in the Capitol Limited paint scheme (suitable locomotive is 88602 Baltimore & Ohio EMD F7 A-B)

87846 – Atlantic Coast Line (suitable locomotive is 88604 Atlantic Coast Line EMD F7 A-B)

87847 – Pennsylvania Railroad "Broadway Limited" train set (suitable locomotives are 88605 Pennsylvania Railroad EMD F7 A-B, 88492 Pennsylvania Railroad GG-1 electric locomotive and 88629 Pennsylvania Railroad EMD E8A)

87848 – Atchison, Topeka & Santa Fe Railway streamliner train set (suitable locomotives are 8860 Santa Fe EMD F7A and 88606 Atchison, Topeka & Santa Fe Railway EMD F7 A-B)

8784, 8785, 8787, 8788, 8789 – Southern Pacific Daylight train set (suitable locomotives are 8809 Southern Pacific Daylight EMD F7A and 88628 Southern Pacific Daylight EMD E9A)

8760, 8761, 8762, 8763, 8764, 8765 – Amtrak streamlined train set (suitable locomotive is 8862 Amtrak EMD F7A)

There are six different passenger cars (in various combinations) in these train sets:

– Sleeping car
– Duplex sleeping car
– Diner car
– Vista dome car
– Observation car
– Baggage car

I developed a corresponding number of decoders for all of them. Someone may think – would not it be easier to develop one or two universal boards? The reason is – each passenger car has its own configuration of windows, as well as different placement of brackets under the roof. Furthermore, if sometime in future I develop interior details for these trains, it will require a corresponding positioning of all LEDs on the circuit boards. In other words, my circuit boards are already prepared for future interior details.

Here are five different circuit boards:


Bottom side – with different quantity and allocation of LEDs:


The set of features is standard for most of my decoders:

Decoder functions: F0 – switches directionally controlled red tail lights at the both ends of the train, F1 – interior lighting. Brightness of both red lights and interior lighting can be adjusted via decoder settings.

I would like to show the last, sixth circuit board separately, as it is a most interesting one. It is a circuit board for Vista Dome car. This coach is actually very attractive in real life, but poorly executed in Z scale. It loses in terms of detail even the old version of type ADümh 101 Aussichtswagen that featured interior details for dome section from the very beginning. I decided to solve this problem and developed a small interior insert that attached directly to the circuit board. Prior to this, I made some research and found some pictures of how the dome looks from inside. For example:





Märklin left dome area of this passenger car unpainted, which also looks very poorly. I fixed this too – roof section was airbrushed, and then support bars were carefully painted manually. In order to improve the look of the car further, I decided to add interior lighting to the dome area too. I developed a small circuit board with two 0402 LEDs that is connected to the main PCB. So, here is it – super-advanced solution for old Vista Dome car:


A small insert with seats was painted with Tamiya LP-30 Light Sand:


Standard brass sliding contacts that I developed for Märklin 4-axle passenger cars fit here too. You can see them already installed on this picture:


Interior insert for dome took a lot of space on the circuit board, so the population of components is very dense. As a result, tracing of this PCB was quite difficult. Nevertheless, I fitted everything without any compromises, including big 2000 μF buffer.

The circuit board is attached to the roof with double-sided adhesive tape. I applied it to the PCB in advance:


First, small circuit board with two LEDs should be fixed inside the dome:


Then, the main board is attached to the roof and wire outputs from trucks are soldered to it:


Now look what a different appearance this passenger car got after upgrade:







And let’s switch the light on:





What a cozy compartment to travel in:







Honestly, I was glad that all measurements were made correctly and that everything fitted ideally from the first ever effort!

Another challenge waited for me with digitizing observation car at the end of the train. At first, I attached a piece of 0.7 mm fiber optic to the red SMD 0602 side-glowing LED using transparent glue, and painted it with silver paint in order to isolate the light from it:



Then I carefully drilled 0.7 mm hole in the roof. It was a bit tricky, as I had to do this at a very sharp angle:



Then I carefully attached the circuit board to the roof and cut redundant part of fiber optic:



Observation car is almost ready:


I also did some additional steps to modernize this train set. First, I replaced old shiny wheelsets with dark nickel-plated ones. Then I installed door windows at the ends of each car (I made them from 1 mm acrylic glass on a CNC cutter):



I decided to improve a tractive power of the matching locomotive as well. Märklin EMD F7 A-B units never were good runners already from the box – with only one motorized A-unit and a sluggish dummy B unit, unlike A-B-A sets with two motors. I replaced a dummy chassis in B-unit with motorized one from German BR 110 electric locomotive (yes, Märklin uses them for F7’s too). Then, second unit received a modified Velmo LDS26306 decoder (LEDs were unsoldered). In order to improve reliability of electric contact, I connected track inputs of both decoders together:


Black wires look like real brake hoses:



And now, one more project is complete – old Märklin’s “dinosaur” got a “second breath” and a nice refreshed look:





Single red tail light is also clearly visible:



One important note: due to the automatic exposure of the camera, brightness of interior lighting may seem to be too high. In real life, the brightness is adequate. Furthermore, it is digitally adjustable.

I decided to add a couple of pictures of a prototypical train that I found on the net:





Best regards,
Alex