Fitting DCC Sound and lighting updates to a Bachmann Colas Class 66

New Project............

Colas 66 running light engine through Peterborough station.



A Zimo sound decoder and speaker are fitted to Bachmann's Colas Class 66, plus the usual lighting upgrade, adding the missing lower marker lights and night headlight.


The Bachmann Colas 66


Fitting an ESU 50334 20x40mm speaker in the fuel tank:

To remove the fuel tank, a major dismantling exercise is required........

The 4 retaining screws are first removed, then the upper body shell is carefully unclipped from the chassis.


The upper body shell flying lead connectors are separated from the main PCB and the two cab mouldings are removed


After the clip in cables are released from each side of the main PCB, the lighting assemblies and main PCB are unscrewed and detached.


The speaker box and bogies are unscrewed and removed


The chassis block is unscrewed from the plastic underframe.....finally enabling the fuel tank assembly to be unscrewed.


The weight and underside switch are unscrewed from the fuel tank moulding.


Exterior view of tank underside, with speaker now glued in place.


Showing the (wet) sealing compound surrounding the speaker.

No blood this time! I managed to carve out the speaker hole without any drill or Stanley Knife accidents for a change!


The battery box end of the ballast weight has been hack sawn from the fuel tank section & refitted to provide a threaded fixing hole.

The inverted top plate is glued together and all the joints sealed, ready to fit when dry.  (The block carries a 2nd screw hole.)


Showing the motor aperture in the newly fabricated top plate & the nearby 2nd mounting screw hole.

The two stand-off ridges are then fabricated and glued to the top plate.

After gluing the top plate in place with liquid poly, the edges and wire holes are sealed with Glue 'n Glaze.

(For best sound quality, the speaker enclosure needs to be completely sealed.)

A coat of matt black paint completes the job.

Matt black paint is also applied to the exposed speaker metal before the tank is refitted and the chassis re-assembled.




Circuit Diagram

Circuit Diagram



Next the lights:

Night headlight LEDs (0603 SMD types) are soldered to the pads conveniently provided by Bachmann on the lighting PCBs.

The missing lower marker lights are fitted in the top of the rear light slots of the lighting shroud moulding. (Nanolight Chip LEDs with wires fed through small holes in the top of the moulding.)

The inner walls of each lighting cavity of the shroud moulding are painted white. The front face of the lighting PCBs is also painted white around the rear lights.


Shroud moulding with Marker LEDs glued in place.

Lighting PCB with new night headlight LED and white paint around the rear light LEDs.

The light from the new marker LEDs cannot be seen directly through the original rear light lens. Instead the white light reflects off the white painted walls of the cavity, producing a low level white glow which can be seen through the rear light lenses when the markers are on. When rear lights are on instead, their light beams directly through the lenses as before. (Although the white paint may make them slightly brighter.)

Colour code of lighting PCB wires:

Day headlight -ve: Green;    Night headlight -ve: Pink (new);   Common Headlight +ve: Orange;    Right rear light -ve: Yellow;    Left rear light -ve: Red;    Common rear light +ve: Blue. 


Removing the motor capacitors:

The three 10NF capacitors wired around the motor are not necessary for DCC operation and can interfere with higher frequency motor they have been removed. However one of the parts also retains the motor lower terminal connecting tab close to the motor body, and without it there is a danger that this might short against the adjacent chassis block. To eliminate this danger, a piece of plasticard has been glued to the chassis block, preventing the tab from touching the adjacent metal side wall.

A tiny piece of plasticard protects the motor connection.


Some Programming Thoughts:

I took a look at Zimo's latest small decoder manual today...... The good news: Its hot off the presses, dated February 2015....... The bad news, its exclusively in German!  So I had to interpret the Google translator results, which do not work well on semi-technical German sentences!

Ploughing through it and comparing paragraph against paragraph using the the most recent UK manual, I homed in on three new capabilities, some of which depend upon recent Version 33.25 or newer.

The first option is a brake key. This enables a high value for CV4 to be used (consistent with over 100 tons of diesel loco continuing to roll down the track, long after the engine has been shut down to idle.) The loco is brought to a halt by applying a braking force via repetitive or continuous pressing of the assigned key.

CV309 is set to the key F number and CV349 appears to set the sensitivity of the brake.

Next comes a method to speed up acceleration if the speed control is first pushed to the max. and then backed off to the desired speed. (Instead of moving directly to the desired speed, when the acceleration would be normal.)

CV394 has bit 4 set to activate this facility i.e. the total value of the CV includes the number 16.

The final discovery is that a key can be defined that will ramp up the engine notches quickly to a preset level. This should enable a max load train start to be simulated by winding up the engine notches to max before the train unsticks and starts to creep forward. (Although it will no doubt take a bit of practice to properly synchronise the wind-up key and the throttle).

CV339 defines the control key for a max power wind up and CV340 defines the peak notch level.

However, the software upgrade to facilitate the above is not yet released, so I'll temporarily run the new Colas loco, using the decoder from my other Zimo 66 pending the release of a new 66 Zimo 644D, that's compatible with the new features.


Connecting up the new circuit:

This time, I've stripped all surface mount parts from the original main PCB. New LED series resistors are glued to thin plastic substrates bonded to the top of the chassis block on either side of the main PCB. Plus the upper marker light and cab light LED series resistors, which are soldered directly to pads on the main PCB. All the solder tags at the ends of the main PCB have been isolated to act as anchor points. The motor, speaker and wheel contact wires have been soldered to the side tags on the main board, instead of using the original plastic retaining clips, to improve long term reliability. Function outputs for Aux 3, 4, 5 & 6 (and more) are also provided on the Zimo decoder, but these are not tracked out on the Bachmann PCB, so thin enamel coated copper wire (off cuts from Nanolight LEDs) have been carefully soldered to the base tags of the 21 pin connector for the required outputs.


The original surface mount components are stripped from the main PCB


Most of the revised LED series resistors are glued to plasticard sheets bonded to the top of the chassis block.


A pair of 1000uF  25V capacitors are connected in parallel to provide a limited stay alive capability.

A small makeover in the cabs at both ends


A white LED has been mounted on a plasticard tab, close to the front right hand wheel.

This will be flashed, synchronised with the triple detonator sound, under PC control.


Using Zimo Swiss Mapping to set the CVs to control the lights:


Zimo's so called Swiss mapping provides a way to set up combinations of lights to be activated by specified control keys

The CVs are arranged in groups of 6 consecutive CVs. With Zimo firmware V34 onwards, there are 13 groups available.

In its simplest implementation:

The first CV defines the key to be pressed. (Key 0 is entered as 29, but all other keys just have their normal F number entered.)

The second CV is normally set to zero.

The third and fourth CVs describe the function output(s) that should be on in the forward direction. (For the headlight FO, enter 14, for the rearlight FO, enter 15. All other FOs just use their FO number.)

The fifth & sixth CVs describe the function output(s) that should be on in the reverse direction. (For the headlight FO, enter 14, for the rearlight FO, enter 15. All other FOs just use their FO number.)


For more complicated combinations of lights with more than just two forward or reverse FOs, two or more Swiss mapping groups can be used, each with the same operating key programmed into the first CV.

Groups can be operated simultaneously, so that for example you can operate the cab light at the same time as the daytime light engine running lights.


There are often lots of different ways that the lighting can be organised and controlled. In the end it all comes down to personal preference.


So first we collect up a summary describing how the lights are required to work:   (The FO numbers are derived from the circuit diagram)

Lighting mode Description Forward FO(s)   Reverse FO(s) Swiss Group Function Key
Cab light (driver's end 2 only) FO5 FO5 1 8
Parking rears both ends FO3, FO(R/L) FO3, FO(R/L) 2 0
Day running Lights (light engine) FO(H/L), FO3 FO(R/L), FO2 3 20
Night Running Lights (light engine) FO1, FO3 FO(R/L), FO4 4 21
Train Haul day (coupled at end 2 FO(H/L) FO(R/L) 5 22
Train Haul night (coupled at end 2) FO1 FO3 6 23


First, in case the Zimo decoder (as delivered) has already been programmed to operate some of the FOs using the older methods of programming, its wise to set these older CVs to zero:

Description CV Value
Key 0 fwd assignment 33 Set to zero
Key 0 Rev assignment 34 Set to zero
Key 8 assignment 42 Set to zero



Then we enter the results into a table of Swiss mapping CV numbers as shown below:


Description CV Value
Group 1      F-Key 430 8
M-Key 431 0
1st fwd FO 432 5
2nd fwd FO 433 0
1st Rev FO 434 5
2nd Rev FO 435 0
Group 2     F-Key 436 29
M-Key 437 0
1st fwd FO 438 3
2nd fwd FO 439 15
1st Rev FO 440 3
2nd Rev FO 441 15
Group 3      F-Key 442 20
M-Key 443 0
1st fwd FO 444 14
2nd fwd FO 445 3
1st Rev FO 446 15
2nd Rev FO 447 2
Group 4      F-Key 448 21
M-Key 449 0
1st fwd FO 450 1
2nd fwd FO 451 3
1st Rev FO 452 15
2nd Rev FO 453 4
Group 5      F-Key 454 22
M-Key 455 0
1st fwd FO 456 14
2nd fwd FO 457 0
1st Rev FO 458 15
2nd Rev FO 459 0
Group 6      F-Key 460 23
M-Key 461 0
1st fwd FO 462 1
2nd fwd FO 463 0
1st Rev FO 464 3
2nd Rev FO 465 0
2nd Rev FO 489 15




Testing with the decoder borrowed from 66731:

As a temporary measure, I've borrowed the Zimo decoder from GBRF 66731 to check out the new Colas machine.  The lighting is all operating as planned, as shown the photos below:

Day running lights

Rear lights on

Night running lights on

Cab light on

(The lights at end 2 behave in a similar way.)

Detonator flash LED on


Driving characteristics:

The Bachmann loco has behaved really well straight out of the box. Using quite high CV3 figures, the take off is silky smooth, with no hint of judder even at the slowest speeds. The decoder has my modifications, as documented in the 66731 page and all is working well. Additionally, I've added the ability to activate the detonator flash LED (although this decoder doesn't yet include the sound sequence). I've also added a parking lights facility with the rears at both ends on together. (Seen a couple of times on diesel locos parked for a limited time in a York station bay platform.) Finally I've also implemented the Zimo up and down volume controls on keys 28 and 27 respectively.

Revised Function Mapping on the test 66731 decoder:


Button Function
0 Parking lights (rears at both ends)
1 Engine start
2 Hi tone horn
3 Lo tone horn
4 Horn ak toot
5 Multi-mode switch (on for heavy start)
6 Force engine to Idle
7 Engine speed-up (for compressor)
8 Cab light
9 Wheel flange scrape
10 Air brakes
11 Brake squeal
12 Detonator flash (if fitted)
13 Starter switch
14 Spirax valves
15 Fans
16 -
17 Shunt mode
18 Zero momentum mode
19 Sound fade out
20 light engine day running lights
21 light engine night running lights
22 Daytime train hauling mode (hook on end 2)
23 Nightime train hauling mode (hook on end 2)
24 -
25 -
26 -
27 -
28 -


This will keep the loco active pending the availability of a new sound project incorporating Paul's new driving arrangements.


The completed Colas 66 on the test track.



Project continues on the "66 Zimo Trio" webpage (click this line to continue)......



Supplier website links:


Monk Bar Model Shop York    Some essential retail therapy was needed here when I discovered that the NRM was closed on my only available day.
Digitrains    Good source for all things DCC including prewired chip LEDs




Click to move to Model Rail Index Page