Adding a sound system to the Hornby Class 60 freight Diesel Locomotive.

Part 2: Fitting a Zimo MX645 decoder to the latest DBS version of the Hornby Class 60:  



I had started researching sound decoder solutions for the forthcoming Hornby red DBS Class 60 release (due Q3 2013). I ended up with 2 main runners, and decided to equip my original Class 60 with a promising ESU LokSound V4 Legomanbiffo solution straight away, while awaiting an equally promising future Zimo solution, which I plan to fit in the new Hornby DBS release in Part 2 of this exercise......... Welcome to part 2!


DB Schenker liveried Class 60 as received. The intended recipient of the new Zimo sound system.


The Project Objectives:

The essentials are to get the lighting colours and relative intensity closer to those of the real locomotive. To re-arrange the circuit to provide full lighting control via DCC commands to the decoder. To enable the rear lights to be disabled when a train is connected to the locomotive. To add a driver in the lead cab and to fit a switchable cab light in that cab. The sound system speaker arrangements need to be at least as good as those of the earlier LokSound equipped Class 60. Beyond these requirements, the Zimo decoder has a lot of function outputs, which would be good to make use of..... perhaps shunting strobes again or maybe something new?????


The Starting Point:

The latest Hornby Class 60 locomotive has a few changes compared to its predecessors. Wire harnesses with inline connectors, link the cab/lighting assemblies with the main PCB . (My earlier 60 used 4 brass tabs on each end of the chassis, which contacted corresponding spring fingers on the bottom of the cab assemblies.) There are now purpose built speaker holes through the roof of the upper body shell, below the exhaust silencer assembly, which were not fitted to the earlier body shell. The shape of the main chassis casting has been changed to lower the side walls directly below the exhaust silencer, to simplify a speaker fit. The electrics are otherwise similar to the original model, with common negative tracking used for the LEDs on the lighting PCBs. The running lights colour and intensity are also as before, with pure white marker lights exhibiting a similar intensity to the headlights. An unwelcome addition to the new model is the liberal use of a sticky black compound, with properties similar to a softer version of Blu Tack. (I've called this material "Black Tack".)



Opening up the Locomotive:

The same clip system holds the chassis assembly and upper body shell together. So fortunately the same process of slipping pieces of card in between the clip halves provides a safe way to separate upper body shell from chassis. Or at least it would have been except for the excess "black tack" sticking the underside of one cab, to the top of the chassis. Once this had been unstuck, only the new cable harnesses kept the two assemblies together. 

First view inside


The main PCB on the chassis assembly looks unchanged, despite a minor difference in the part number..... so its reasonable to conclude that we still have to deal with a pair of classic Hornby negative ground lighting PCB assemblies.

Same old PCB, so we're going to need a few PNP transistors!


The shape of the main chassis casting has been changed to lower the side walls under the new speaker holes. I do not think there is room for a full size ESU 50334 speaker enclosure here, but a reduced height version would definitely fit.

Side walls lowered to just above the drive shaft




Looking in more detail at the cab assemblies:

The cabs are held in place with a blob of solidified compound forming a breakable bond between the body shell roof and the rear cab bulkhead.

The cab assemblies have to be removed to enable the marker light LEDs to receive a coat of yellow water colour paint. This reduces their intensity and gives a more accurate colour.

However, the new cab assemblies are not in good shape! The glue application is poor with several examples of glossy glue puddles under the levers around the driver's seat. In one cab, the rear bulkhead came away and the driver's seat was not properly fixed.... despite very visible evidence of excess glue. Liquid poly Repair work was needed and some matt paint touching up to camouflage the poor glue work adjacent to the new driver who is now super glued in place.

Showing poor quality glue bonds on the Front cab


Rear cab.


Front cab with new driver added & seat plus rear bulkhead both repaired.

More problems were found around the running light LEDs. The plastic matrix pieces used to prevent cross coupling of light between adjacent chip LEDs, have been fitted, with "black tack" forming a seal between the PCB and the plastic. Good for stopping light leakage, but unfortunately, the sealant has spread out to partially cover the illuminated part of some of the LEDs. This had to be carefully scraped off the LED "windows" affected.  On one cab, the matrix piece had bonded to the paint surrounding the lenses fitted in the upper body shell moulding. When the cab was separated from the body shell, that matrix piece was left behind, but left residual "black tac" surrounding and partially covering the surface mount LEDs.

Matrix piece on the left was replaced after the "black tack" was removed, and glued back in place.

The Matrix piece on the right still includes "black tack" which has oozed out around the LEDs.

In the end, I removed the other three matrix pieces and cleaned off the black tack completely.


The quality of the internal assembly looks much better in my earlier example of the Hornby Class 60, which looks pristine inside, in comparison with the rather shoddy appearance of the cabs of this latest example. The liberal use of sticky "black tack" doesn't help, but the poor glue work is not good news. I wonder if the new units are made in a different factory?  Despite the disappointment, it all looks fixable, so onwards and upwards!


Initial thoughts on decoder placement:

With the majority of connectivity at each end of the upper body shell, it should be possible to mount the decoder and its interface circuit in the upper body shell. The remaining decoder connections to the chassis for the motor and wheel contacts could be handled via the 8 pin connector, with remaining circuitry on the main PCB removed in the usual way, to give increased head height room for the decoder above. 

There is just enough room to mount the PNP transistor circuitry on the rear face of the cab bulkheads. This leaves plenty of room to mount the decoder in the upper body shell roof underside, directly above the cleared area of the main PCB. The speaker can then be mounted either directly below the exhaust silencer, or above the twin side cooling group vents, as in the earlier LokSound equipped Class 60.


Lighting Circuit Diagram:

Once again, Hornby have chosen to use a common negative supply for their lighting PCB assemblies, so interfacing to the common positive supply of the decoder is done using several PNP transistor invertors.

The extra function outputs available in the Zimo decoder enable separate connections to be made to all lighting groups, which can then be combined to provide day or night running lights, with or without rear lights and separate control of the cab light and either strobe lights or any other ideas that occur to me.

I must research CMOS inverters, if they are still available for 16V supplies and with a 10mA capability, they might provide a smaller component count solution!


Updated Cab Assemblies:

The messy black Tack substance was removed from the bottom of the cab assemblies and from the lighting PCBs around the LEDs. The transistor inverter circuits were glued to the rear of the cab bulkheads and directly wired to the pads on the lighting PCBs. The faulty glue bonds were repaired and the glossy areas of the cab control panels were painted with matching matt grey paint. The marker light LEDs were over-painted with yellow water colour paint, to reduce intensity and to look a bit closer to the colour of the originals.

Cab assemblies ready for re-fitting.


Decoder interfacing inverter circuits on the back.


Wired directly to the lighting PCBs. (Decoder ground & positive wires to be added later.)


Marker lights painted with yellow water colour paint to reduce intensity and better reproduce the colour of the originals.


Preparing the Chassis Assembly:

1) Main PCB:

All the surface mount components have been removed from the main PCB to give plenty of space for mounting the Zimo decoder in the roof above the main PCB.

2) Adding a magnetic detection system:

A Hall effect device has been glued to the underside of the lead bogie, directly between the front pair of wheels. The three wires from this device are routed up into the main body in parallel with the wheel pick-up wires. The Hall Effect sensor is only just above rail head height, so it will be low enough to detect magnets placed flush with the code 75 rail sleeper tops. (See the magnetic sound control page for more details of the system)

Oh Dear! Another Hornby assembly error! (discovered when routing the Hall sensor wires through the bogie)


This one is a bit more serious as it effects the running of the locomotive. The centre wheelset of the lead bogie has very little side to side movement freedom. It is held hard over to one side by the brake shoe moulding. Looking more carefully at the bogie, the gap between the centre axle and the axle nearest the locomotive centre is slightly smaller than that between the centre axle and the outside axle. Because of this, the spacing of the brake shoes between the axles is different. This means that there are left hand and right hand brake shoe mouldings and it appears that the wrong hand moulding has been fitted on one side of this bogie. (The other bogie is fine, with the correct parts in place.) My only safe route forward is to cut the offending brake shoe from its moulding and try to refit it far enough back from the wheel to stop the obstruction......the problem is that its soft plastic, which is notoriously difficult to glue successfully.... So for now, I've bent the problem shoe away from the wheel and I'll periodically check to see if the wheel is still clear.

The other bogie is fine.


I have obviously invalidated any warranty as a result of the work already done....... but I suggest any other Class 60 purchasers might like to take a look at this detail before making any changes! And in the unlikely instance of anyone from Hornby reading this..... Please be aware!


Back to the upper body shell:

1) Cab light:

The underside of the roof within the manned leading cab was painted matt white and a daylight white chip LED was glued near the centre of the cab roof.


2) Speaker:

The slots in the audio path under the exhaust silencer look very small, so I've decided to mount the speaker in the same position as the earlier Class 60, facing downwards, above the twin side vents.

ESU 50334 40x20mm speaker enclosure, glued in place.


The Zimo Decoder:

Pin-out diagram from the Zimo manual


Modified 8 pin connector providing motor, wheel contact and magnetic sensor interfaces between the upper body shell and the chassis assemblies


Making the Upper Body assembly ready for the decoder:


The cab assemblies were wired and re-located at either end of the upper body shell and the ESU 50334 40x20mm speaker was wired then fitted and sealed into its enclosure. The decoder will fit near the centre on the roof underside, so there is still room to add an additional speaker below the exhaust silencer later. (The wires will be glued in place and the two Blu Tack wire clamps removed when the unit has been successfully tested.)

The body shell needs to retain flexibility to allow its clips to engage and release, so it does not seem wise to glue the cab assemblies to the body sides, even after testing.


The lead cab, held in place with removable BluTack.

Trailing (unmanned) cab, held in place with removable BluTack.

The lights were checked using a bench power supply, to confirm correct operation. I decided that one Class 60 with shunting strobes was enough, so I'll have 3 spare function outputs available on the Zimo decoder, until I can think of a use for them!


Making the decoder assembly ready for the Upper Body:

I've now taken delivery of a Zimo MX645 decoder from Digitrains, equipped with their current Class 60 sound project. I've added the additional wires to the appropriate pads  on the rear of the decoder PCB and bonded the decoder to the upper body shell roof with double sided foam tape.

The leaflet included with the decoder, marked up with the additional connections made to the decoder, in red.


Some careful measurements indicate that three 1000uF 25V capacitors should just fit below the exhaust silencer, giving 3000uF of "flywheel storage". Brief pause while I get some more thin heat shrink sleeving and some strip-board from Maplin.....

Lots of connections to wire up and insulate!


All in place......hope it all works!


Zimo Decoder CV Set-up:

1) "Swiss mapping" for the lighting control, using buttons 20-22:

 NB: The front cab with driver in place, is at end 2 on the circuit diagram.

The Requirement:

F(0) = normal light engine day running       (Day headlight & marker lights at end2 & rear lights at end1) Forward  +  (Day headlight & marker lights at end1 & rear lights at end2) Reverse.

F(0) + F(20) = Night light engine    (Night headlight & marker lights at end2 & rear lights at end1) Forward  +  (Night headlight & marker lights at end1 & rear lights at end2) Reverse.

F(0) + F(21) = Day running with train  (Day headlight & marker lights at end2) Forward + (rear lights at end2) Reverse.

F(0) + F(22) = Night running with train  (Night headlight & marker lights at end2) Forward + (rear lights at end2) Reverse.



Function Outputs Forward

Function Outputs Reverse


FO 0Fwd (white) + FO 4

FO 0R(yellow) + FO 3

F0 + F20

FO 1 + FO 4

FO 2 + FO 3

F0 + F21

FO 0Fwd (white)

FO 3

F0 + F22

FO 1

FO 3



CV Listing:





0 (F)

Fwd Outputs



0 (R)

Rev Outputs




Button F (20)




Button M  (0)




1st Fwd O/P




2nd Fwd O/P




1st Rev O/P




2nd Rev O/P




Button F  (21)




Button M  (0)




1st Fwd O/P




2nd Fwd O/P




1st Rev O/P




2nd Rev O/P




Button F  (22)




Button M  (0)




1st Fwd O/P




2nd Fwd O/P




1st Rev O/P




2nd Rev O/P






2) Cab light control:

The driver's cab light is also switchable via normal button control, using the F8 button. The decoder is set for enhanced mapping, with CV61 set to 97.  So CV42 needs resetting to 64 for the FO5 output.


3) CV verifications and some possible changes:


CV Number

As receved

New Value

Master volume




Sound Set to larger layout




Set to 128 speed steps Via controller    OK

Bemf sample rate (87 rec for 3 pole)




Motor drive freq. (0=20kHz, 32=40kHz) 112 32  32

Check function mapping regime




Map cab light (FO 5) to button 8




Map day light engine lights to button 0




Map day light engine lights to button 0




Start Voltage




acceleration delay




deceleration delay




max speed




half speed




Bemf voltage ref (Max speed 60mph)


0 (=Vrail/10)


Check SW Version




Reset button 9 default




Reset button 10 default




Reset button 11 default




Reset button 12 default




Start delay with sound on 273 20 35


4) Magnet detection Zimo CVs:

To select the sound clip activated by the magnet transit:  Use Pseudo programming routine after setting CV300 to 111 then use the normal sound selection procedure to identify the clip required, followed by F8 to save the choice.


CV341      0-255     Time in seconds sound is played back;   except 0=play sample back once.  (Set to 0)

      CV739      0-255     Volume of sound triggered by Switch input 1  0=255=max   1-254 proportional. (Set to 120)


5) Function Mapping Summary:


Button Action
0 Day running lights (light engine)
1 Engine start/stop
2 Horn (playable)
3 Horn (playable)
4 Multi Mode (moves notch transition speeds up & reduces CV3&4)
5 Flange scrape
6 Coast
7 Buffering-up
8 Driver's (end 2) cab light
9 Coupling
10 Brake squeal
11 Sanders
12 Spirax valves
13 AWS
14 Fire bell
15 Compressor
16 BIS (Pre start engine priming)
17 Door open & slam
18 Dispatcher whistle
19 Fade all sounds
20+0 Night running lights (light engine)
21+0 Day running, end 2 only
22+0 Night running, end 2 only


All working fine!!!!


Full snow plough plus hook & hoses fitted to the front.

(Also the magnetic detector & its cables under the bogie, are now painted matt black)


Sorting out a flashing rear light for the Oil tanker train hauled by 60007:

The rear tanker is modified to include a new rear light, driven by an astable multivibrator circuit. This should be an improvement on my previous (simpler) circuit that used a flashing LED as the "on- time" can be adjusted to better simulate the brief flashes off the real units used on U.K. rails. A tanker with a loose ballast weight fault was chosen for simultaneous repair of the loose weight and the application of the flashing rear light.

The Bachmann tanker was dismantled to remove the cylindrical tank. Rectangular holes were then cut in the flat base area of the tank above each bogie. The ballast weight was then extracted through one of the holes. The weight strip was then shortened with a hack saw to a length that just fitted between the apertures in the bottom of the tank. It was then insulated (in case it ever comes adrift) and fitted with double sided foam adhesive pads along its length. It was re-introduced into the tank with the aid of a piece of string that was taped to the top surface of the weight, and passed through the tank first. The string enabled the weight to be kept under control until it was firmly pulled down to bond it to the tank base between the apertures. A firm foam sponge was then cut into sections that could just be squeezed into the tank, expanding, once inside to completely fill the tank above the ballast weight and hence reinforce the foam tape bonds to the base of the tank.

Tank underside view (with ballast weight refitted between the two apertures).


The circuit was tested in breadboard form using a bench power supply and optimised for the on and off times of the flashing sequence. The resultant circuit diagram is shown below:

The frequency is approx 2 flashes per second and the flash on period is short to simulate a strobe.

(The two diodes in series with the transistor emitters prevent reverse breakdown of the base emitter junctions when the base voltage shoots up to maximum, which could otherwise blow-up the transistors.)


The circuit is rebuilt into a shape that can be slid into the tank through one of the apertures. The LED wires and wheel contact wires emerge from the aperture, ready for later fitting.

Circuit fixed to a plasticard substrate. The 0.22uF caps are huge....I'll use small electrolytics & lower value resistors next time!


The plasticard is glued to the aperture edge. (A quick slice by the Stanley knife will facilitate removal if repairs are ever needed.)


Next another plasticard Dorman Mk3 rear light shape!

Just needs some red water colour paint over the lens & a red rectangle below


Phosphor bronze wheel contact strips super-glued on to plasticard supports fixed to the rear bogie. (Coupling also removed.)


All complete and working well! (Difficult to catch the flash on camera though.)



Youtube Video:      Click here to see and hear the locomotive in action



Supplier website links:  


Hornby The DB Schenker Class 60 unit above was purchased early, direct from the Hornby shop, when this was the only source.
Digitrains A good source of all things DCC including pre-wired chip LEDs from DCCC and Zimo decoders.
Rapid Electronics A good low cost, high speed supplier of electronics components etc
Maplin A convenient local source for electronic components such as resistors and transistors


The photos of the Class 60 model were taken hand held on the kitchen worktop using a Canon IXUS 220HS.    


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