The Problem:

The problem locomotive lighting fails to illuminate the lower marker light immediately adjacent to the active headlight. (This is correct on Class 70 locomotives, but NOT on Class 66.) 

Correct Class 66 Arrangement

Day Running Front	Night Running Front	All Running Rear

Behaviour of The Problem Locomotives

Day Running Front (Right lower marker off)	Night Running Front (Left lower marker off)	All Running Rear (O.K.)

What is the source of the problem?

The lower marker light LEDs, headlight LEDs and rear light LEDs are located on the small lighting PCBs mounted close to each end of the chassis. In problem locomotives, the trackwork on these boards is configured in such a way that the lower marker lights are only illuminated when the headlight on the opposite side of the locomotive is activated. In order to fix the problem, operation of headlights and marker lights needs to be made independent.  

The problem locomotives use only 4 wires between each lighting PCB and the main board. Correctly operating Hattons Class 66 locos use 5. The fifth wire provides the necessary independent control of the two lower marker light LEDs (which operate in parallel albeit with individual series resistors).

How can we fix it?

This depends on a key issue: The small lighting PCBs are glued into slots in the chassis metalwork. If the glue bond can be broken to allow the boards to be removed intact, then some fairly intricate track modifications can effect a fairly simple fix.

Removing the small lighting boards:

If the boards do not succumb to a firm repetitive forward and backward motion when gripped between thumb and forefinger, removal may still be possible by first removing the air dam / buffer beam assembly and then applying leverage between the bottom of the lighting board and the chassis, using a small very thin bladed screwdriver. (Be careful to insert the blade below the board edge and do not apply upward force just to the moulded plastic cover attached to the front of the lighting board.) 

If the boards are impossible to remove intact, then a second option is to obtain replacement boards from a specialist lighting company "Illuminated Models" (see the bottom of this web page for their web address) The new boards need to be wired in, soldering the original wiring plus one additional wire to quite small pads near the top rear of the new boards. The moulded plastic board covers are re-used on the new boards, so be careful to keep these intact if you decide upon a forced removal of the original PCBs.

A more difficult and far less elegant solution provides a further way to solve the problem. See Plan B below.

Plan A...... If the lighting PCBs can be removed from the chassis intact:

(With many thanks to Howard for the loan of his Freightliner lighting board)

Two track cuts, a link wire and a new 5th wire back to the main board will provide a solution for each lighting board.

NB: The original board wire colours maybe different on your loco.

The track cuts are shown in red. A thin insulated link wire connects two of the solder pads, shown in dark blue.

Finally an insulated wire (shown in light blue) connects the linked pads back to the main board.

The new wire to the mother board from each lighting board connects to the vacant "W" solder pads at each end of the main board.

A modified board

Its a bit tricky as the board is on the small side...... but if you can successfully extract the lighting PCB from the chassis slots without damage, this a much more straightforward solution than the alternative approach described below!!!!

With many thanks to Howard for the loan of his board to plot the circuit, identify the fix and confirm it all seems to work!

This was the kind of approach I hoped to use on my own large headlight 66 to fix the problem...... but unfortunately, unlike Howard's 66, the lighting boards in my loco were so well glued in place that it was impossible to remove them without writing off the boards. The following section describes the alternative steps I had to take.

Plan B...... Another solution if the lighting PCB assemblies are so firmly fixed in place, that intact removal is impossible:

This was the situation I found on my own locomotive. These modifications to obtain correctly operating lights are quite involved and probably not for the feint hearted:

The idea is to remove the original headlight LEDs so that the original wiring only powers the marker LEDs. New LEDs are then glued within the lighting board plastic cover. These are wired directly back to the main PCB assembly via discrete series resistors. The main PCB connections are then re-arranged to restore the correct connectivity.

The plastic cover (LED shroud) with 4 rectangular apertures is removed from the lighting PCB.

 

The top two chip LEDs are removed from the PCB and any excess solder or debris is carefully removed from their solder pads.

 A coat of super glue is then carefully applied over the 4 exposed solder pads to insulate them.

Two pre-wired white chip LEDs (e.g. DCC Concepts Nano LEDs) are glued into the upper two apertures in the plastic cover, beaming directly through the small apertures in the front of the cover. The LED wires are routed through slots cut into the top edge of the plastic cover. the plastic cover is then glued back into place on to the front of the lighting PCB.

The ultra thin LED wires are routed over the top of the lighting PCB and then downwards, to lie beside the original wires, leading to the loco main PCB assembly. 1k5 Series resistors are installed in the negative LED leads en route to the main PCB. The resistors are super glued to the rear of the speaker at one end and the plastic mounting plate for the stay-alive super-cap at the other.

At the drivers end of the locomotive

And......At the other end of the locomotive.

The positive new LED wires are connected to the common positive solder pads used for the top marker and cab light wiring as shown above.

Main Board connections:

 The original inner pair of wires (grey and black on my loco) from the lighting boards are removed from the loco main PCB solder pads labelled "day" and "night". They are then connected in parallel, to the main PCB pad "W". The wires from the new headlight LED negative lead series resistor wires are connected to the appropriate main PCB "day" or "night" pads. A table showing the pad markings and the corresponding wire destinations appears below.

Conclusions (a):

It is well worth spending time to extract the lighting boards if it is possible to remove them from the chassis without damage. It is then possible with care to modify the boards as shown in Plan A and achieve a quick solution, as demonstrated in the Colas 66 photograph at the end of the Plan A section.

If the above proves impossible, then the alternative Plan B route, also described above, achieves an equivalent result, but involves considerably more work and time. With hindsight, the use of new warm white headlight LEDs would have been a better move, as the incorrect yellow markers would have then been less conspicuous.

In fact this eventually prompted me to give the Illuminated Models replacement lighting boards a try.... These have pure white markers with warm white headlights, which looks much more realistic. I found a way to extract the original boards after all. (Remove air dam/buffer beam assembly and lever out with a small sharp screwdriver between the chassis and the bottom of the PCB.)

The only worry I had was that some circuit tracing revealed that the replacement board uses parallel connected pairs of rear light LEDs which share a common series resistor. A similar arrangement is also used for the two marker LEDs on each board. Now the boards work well, with no obvious imbalance in intensity between the parallel LEDs, so my concerns maybe unfounded, but I was lead to believe that LEDs connected in this way may not share current in an identical manner... safer to use individual series resistors for each LED (as per the Hattons design) or to save a resistor, by connecting the LEDs in series via a single series resistor instead, which of course ensures equal current flow in each LED.... Despite the theory, my new boards seem to work fine, so they have now replaced the original plan B solution in my Freightliner locomotive.  (See photo below.)

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