DCC conversion and LED Lighting update of the Hornby Class 43 HST Pair
This web page provides a summary of the process adopted to incorporate DCC decoders and correctly operating external LED lighting in the Cross Country Trains variant of the Hornby Class 43 diesel pair (OO gauge).
The page has now been updated with a modified approach to the task, based on experience gained in several subsequent HST conversions and a switch to ESU motor control decoder .
Note that the smaller pictures can be enlarged by clicking on the image.
Hornby Model Cross Country High Speed Train with Class 43 locomotives at each end
|DCC Conversion Approach:
The plan is to use a 4 function plus "back emf" motor control decoder (ESU LokPilot V4 now the preferred choice) in the power car and a 4 function only decoder (TCS FL4) in the unpowered rear car, providing correct operation of headlights, marker lights and rear lights during day or night running.
The Hornby lighting system as found "Straight out of the box":
The Hornby lighting solution uses a single red chip LED (2) for rear lights, a single white chip LED (1) for the side marker lights and a single white chip LED (3) for the right hand headlight. These are mounted on a small PCB fixed to the front of the driverís cab moulding. Three spring fingers provide the electrical interface to corresponding metal pads at the front of the chassis unit.
A shielded light pipe terminates in the outside pair of lighting lenses at the front of the locomotive. This can be illuminated via adjacent LED (1) or LED (2). The light pipe is mounted within a black plastic shield assembly, which is attached to the front of the LED PCB. Note: Both the marker lights and the rear lights are too bright in the original Hornby model!
The right hand headlight lens moulding incorporates a rear light pipe. LED (3) is used to illuminate the rear of this lightpipe, via an aperture in the plastic shield assembly mentioned above. Note: The headlight is too dim!
The left hand (night headlight) lens has a small rectangular protrusion at the rear, which mechanically engages with the plastic shield moulding. There is no provision for illuminating this lens.
The detailed shape of the plastic shield moulding successfully prevents unwanted light coupling between the lights.
LEDs (1) and (3) are wired in parallel and activate during forward running. LED (2) activates during reverse running.Note: In the power car LED PCB assembly, a common negative return is used for each of the LEDs. However, in the trailer car, although the small LED PCB is identical, the LEDs are fitted the opposite way round, to provide a common positive return. (I discovered this curious arrangement the hard way, having previously assumed the two PCBs were identical!)
Grubby Grand Central Class 43 showing daytime lighting
Grubby Grand Central Class 43 showing rear lights
|The new lighting
The left hand headlight is to be made operational and brighter than the original right headlight.
The right hand headlight is to be made brighter while the rear lights and front marker lights are to be reduced in intensity.
It will be possible to operate with the following lighting options:
1) 1) No lights
2) 2) Daylight right hand headlight plus both side marker lights at forward end / rear lights at rear end (activated by button 0). (As shown in photos above).
3) 3) Night left hand headlight plus both side marker lights at forward end / rear lights at rear end (activated by button 1)
4) 4) The cab light will operate in the forward car only when activated (by button 2).
The wheel contacts (red & black wires) plus the motor wires (orange & grey) are connected via the 8 pin socket
The PNP transistors are BC559c (almost any small signal PNP will do) and the diodes are 1N4005 (complete overkill)
Unpowered Rear Car
The trailer car PCB uses a common positive circuit so PNP transistors are not required
The diodes are 1N914 (but almost any silicon diode will do)
New bright Left hand headlight:
Use a pre-wired daylight white chip LED, fitted immediately behind the left headlight lens. (e.g. DCCC nanolights available from Bromsgrove Models & Digitrains.)
First, remove the left headlight lens. File down the clear plastic block on the rear of the lens, significantly reducing its thickness. Replace the lens (correctly orientated) into the front body shell.
Glue the chip LED to the front of the rear/marker lightpipe shield, to beam directly at the rear of the lens. Paint the area around the chip LED white.
New brighter Right hand headlight:
Use a similar approach to that described above, removing the convoluted lightpipe from the rear of the right hand lens and filing any residual clear plastic at the rear of the lens to give enough room to fit the chip LED.
Again, glue the chip LED to the front of the rear/marker lightpipe shield, to beam directly at the rear of the lens and paint the area around the chip LED white.
Power Car cab and lighting assembly refitted with extra leads glued and taped
|A Revised View on Lighting
After doing several Hornby HST updates, I no longer recommend making any changes to the lighting PCBs. It is very difficult to dismantle the PCB assembly from the front of the cab moulding, without breaking the supporting plastic lugs. These are difficult to successfully repair and this can make the whole PCB assembly loose on the front of the cab moulding, making the spring electrical contacts very unreliable. The consequence of not making changes to the lighting PCB is that a pair of PNP transistor switches are needed to interface the power car common negative LED circuit with the decoder, but this is a simple task compared to the lighting PCB modifications!
The one modification that IS required to the lighting PCBs, is to disable the original headlight LED. This can easily be done, without dismantling the assembly, using a 1.5mm drill to "open circuit" a convenient plated through hole (or via) in the PCB as shown in the photo below.
Disabling the original headlight LED
Optimising the series resistor values on the first HST to be modified
|Adding the new power car
The original printed circuit board is used to mount the new parts. The Hornby circuit is not required at all for DCC operation, so all the original surface mount components are first removed (using a pair of miniature soldering irons). Only the 8 pin socket is retained. Any residual solder that might be at risk of shorting adjacent solder pads together is carefully removed using solder wick, because the motor and wheel contacts, connected to the 8 pin socket will be used again. Except for the two centre tags at each end of the PCB (which connect to the wheel contacts) track connections are cut to the remaining 4 outside tags at each end of the board, isolating the tags from the PCB tracks. These tags will be used as anchor points for the original lighting wires at the front end of the PCB and for the new headlight and cab light wires from the upper body shell, at the rear end of the PCB. The new circuit parts are wired together and then fixed to the PCB, using double sided adhesive foam tape. (The circuit is shown in the diagram above.)
|Fitting the decoder:
The ESU LokPilot decoder is mounted in the holder on the rear platform of the Power Car. Wires are run on either side of the fan drive housing, to the PCB. Motor and wheel contact connections are made using the 8 pin connector. The remaining wires are extended, then soldered to appropriate points on the new circuit. The wires are glued to the side of the fan housing to ensure that they do not obstruct the main locomotive fixing screws.
After soldering the new headlight and cab light wires from the upper body shell, to the solder tags at the rear of the main PCB (which have been isolated for this purpose by local track cuts)...... The upper body shell is re-united with the chassis unit and the 4 fixing screws are re-fitted.
Ready to re-fit the upper body shell
|Modifying the unpowered
The rear car cab and lighting assembly is modified in a similar way to that in the power car. (described above). However, the modifications to the circuit board are much simpler, as the rear car lighting board uses a positive common supply for the LEDs.
The Hornby components are all removed, except for the 2k2 resistor in series with the cab light. Leaded resistors and diodes are fitted in line with the circuit diagram shown above. (This time it is possible to make use of the original PCB tracks and pads to mount the new components after a little track cutting. The TCS function decoder (FL4) is mounted in the purpose built slot at the rear of the car and its leads are soldered to the relevant points on the circuit.
Extension wires, for the new headlight wires and cab light wires, are fitted inside the upper body shell in a similar way to that shown for the power car. These are soldered to tags on the main PCB that have been isolated by track cuts for this purpose. The upper body shell is then re-united with the chassis and the 4 fixing screws are re-fitted.
|The Decoder CV
Power Car ESU LokPilot V4 Programming
Unpowered Rear Car TCS FL4 Programming
Test running the HST:
The locomotive roof needs the addition of some matt black to simulate the liberal coating of exhaust soot that accumulates on the real locomotives. The jury is still out on the Hornby Mk3 coach burgundy roof tops and Class 43 rear roofs. I have found photos showing matt black roofing, two tone grey roofing and just maybe an occasional hint of slightly soiled burgundy roofing. My daughter insists that the Cross Country HST she last used between Sheffield and Leeds had a totally matt black coach roof above the cant rail markings. I'll hold off on a paint job for this area in the hope of better photographic evidence that at least one HST set has the burgundy roof, as I'm worried about damaging the cant rail strips with masking tape .....Time will tell.....
Matt Black diesel exhaust fallout applied to the Class 43 roofs
|Supplier website links:
The photos of real class 43s were taken at York during 2010. The photos of the model were taken on the kitchen worktop using originally an SLR on a tripod & more recently, a hand held Canon Ixus.
|Discontinued Original LED PCB Modifications
for information only.
As explained above, access to the LED PCBs almost certainly results in damage to the mounting lugs at the rear of the cab moulding. These are difficult to successfully repair, even with super glue. The result can be an unsound lighting assembly, with unreliable connections at the sprung contact points. I've included this section (from earlier HST conversion work) only to show the circuit diagrams and layout of the boards for information.
To avoid the need for PNP switching transistors, the tracks of the power car lighting PCB can be cut and bridged to change the LED connections to have a common positive connection. This greatly simplifies the decoder interface circuitry. Further adjustments are made to disable the original LED 3 and to provide anchor points for the wires from the new chip LEDs mounted on the lightpipe shield. The revisions are shown in the diagram below.
Power Car Lighting PCB modifications
The unpowered rear car PCB assembly has the LEDs soldered into the same positions, but back-to-front.
The common positive is therefore already in place. Further revisions are shown below.
Unpowered rear car Lighting PCB modifications
The spring fingers were replaced with hard wired connections in the rear car, where the extra space made this approach viable.