Kernow/Bachmann class 205 Through Wiring Anomaly - solved: now "how I did it"

[SRman]

I wonder if I can call on the collective intelligence and experience here, please.

I have been preparing a centre coach, using a Replica Railways BR non-gangwayed coach on a spare 4 CEP TSK chassis, to convert a Bachmann/Kernow Models 2H unit into a 3H. Until now, I have been concentrating on matching the colours, but I thought it was time to start wiring it.

The CEPs are wired slightly differently to the 2H and 2 EPB units, and when coupled up, the interior lights become directional (i.e. they work in one direction but not the other). No problem, thought I, I'll bypass the PCB and wire the couplings straight through, then use the bogie pickups to wire the lighting boards in the roof. I duly wired the couplings straight through, and the lighting in the centre car and the Driving Trailer all became directional. I tried crossover wiring but they then became directional in reverse, with the interior lights and headcode only lighting up when reverse was selected.

This is really odd, because the coupling bars when going from Driving Motor to Driving Trailer are straight through anyway, so what is going on. I am at a complete loss as to how this can be happening.

Has anyone else done this conversion, and what did you do to fix the problem?

I should add that my unit has DCC sound using an ESU LokSound decoder, but even on DC these lighting 'glitches' are happening. I was in two minds as to whether this belonged under 'Electrics' or in the DCC section, but I think it is more a straight electrical problem.

Edited August 8, 2017 by SRman

[John ks]

Does the lead unit work properly by itself

Does the trailing unit still work correctly when connected to the lead unit?

Do these units use the coupling bar that has 2 conductors in it?

Does the trailing lighting consist of interior lights & a directional light for either a headlight or route indicator panel head code

 

When you say you wired the centre unit straight through is the interior light wiring completely separate from the straight through wiring. I.E. Have you wired the centre unit like the bottom drawing (#2), If it is wired like this then the lights in the centre unit would always be on(depending on the track voltage)

 

I think the wiring in Bachmann is done like I have indicated in drawing #1

The 2 diodes give you the decoder common so that the 2 functions have a path to complete the circuit The actual circuit may be more complicated so that the lights work on DC & DCC

 

 

I am not sure if this may be any help but with out being able to see them in person this is the best I can do. Pictures of the circuit boards in the centre & trailing units may help

 

John

Edited August 5, 2017 by John ks

[SRman]

Hi John.

 

Thanks for the input. The couplings use the rigid bar with two contacts and when the DMBS and DTC are connected as originally supplied, all works perfectly, This is why I cannot understand how they don't work correctly when I bypass the PCB completely in the centre coach and just wire the two coupling connections directly to each other. There is obviously something else at play here but it has baffled me.

What should happen is that the interior lights and the headcodes (reversibly white or red) all come on with function 0. 

[John ks]

Do the wires from the couplings only go from one coupling to the other, IE there is no connection to any circuit board in the centre unit

If this is the case then I am also at a loss why the trailing coach misbehaves, unless one of the coupling bars is not making correct contact.

 

From your description of the headboard/interior lights operation  I now think the trailing unit may be wired like the new drawing(I have included this as a reference, the circuit board in this unit May be more complicate than shown. you should not have to alter the wiring in the trailing unit)

 

If the Lights are LEDs (which I think they are) then there will be resistors in series with the LEDs

 

 

For the centre unit interior lights to work the same as the trailing unit the wiring would have to be configured as shown

Remembering that LEDs will need resistors in series

​You may be able to reconfigure the circuit board in the centre unit to work But without knowing this board I cant be sure how

 

John

[SRman]

The 4 CEP trailers were wired differently because their lights were on function 1, while the headcodes were on function 0, but permanently lit in both directions, so still only using two functions, just not using the directional facilities. I am not aware of any wires going from the couplings to the PCB, but I'll unscrew it and double check what's happening there.

However, my bypassing it completely should not have caused the odd behaviour. I am now thinking I'll dispense with the PCB entirely (just to be sure there aren't any other connections), then I'll wire the bogie pickups directly to the lighting board in the roof while the coupling wires go straight through. As I have run out of time this weekend, this will probably wait for a bit more spare time.

I will pay due attention to the need for resistors in the lighting circuits and will check to see if they are on the lower PCB (the one I am going to dispense with) or the upper lighting one.

Once again, thanks for your input, John. I will try to get a decent photo of both sides of the PCB to see if either of us can see anything that would give a clue.

[SRman]

John, I have given further thought to this overnight, and feel you may be right about one of the contacts not working; it may be something as simple as that. That's where I will start when I next look at it.

[SRman]

Further to that last post, I removed the base PCB and checked all the wires, contacts and connections from the couplings, bent one of the coupling contacts slightly to secure it, then tested on the track with the DMBS and DTC connected and it all worked perfectly, so it does look like it was the simple solution: a dud contact.

Next I will have to do battle with the lighting board. Unlike the EPB/2H boards, the CEP one is divided into two separate halves with the contacts reversed in the middle. Since I always run with all the lights on anyway, I will leave the centre coach lights wired directly to the bogie track pickups to simplify things. That means I'll wire a crossover connection on the lighting board to feed the correct supply to each side.

[SRman]

Now that the through wiring is working, I attempted the bodges on the lower PCB, with something of a failure. I wired the bogie pickups to the side contacts leading to the LED connectors - these go through a bank of resistors, so if I bypass the PCB entirely, I'll have to add new resistors into the circuits.

 

Next I soldered wires intended to link the lower and upper PCBs. In trying to be clever and simplify the the wiring by reducing the number of connection between boards, I soldered a cross wire linking the two sets of centre contacts, Ground to Ground and LED to LED - I fear that may be where I have gone wrong because when placed on the track it buzzes ominously, even without the upper PCB connected.

So, the next experiment will be to eliminate the crossover wires, and link only the contacts at one side of the centreline (across the PCB, not lengthwise). If this works, I'll do the other two sets of contacts, keeping them separate - basically leaving the two PCBs set up as two halves each for wiring. 

I'll try to post pictures next time to show more clearly what I am trying to describe.

[SRman]

Pictures following.

I persevered with the wiring as I thought it should be and tested on DC power. Once it was all connected up, the lights worked perfectly on track power. On DCC, it still gave the buzzing, and they seem dimmer, so possibly the DCC form is acting as a form of AC and causing the buzz, There are no short-circuits or heating up of any elements, so I may have to live with the buzz for a while. Maybe eventually I'll add a diode bridge to cure that.

To make things easier for disassembly and adjustment, I soldered a 2-pin connector to allow the body and upper PCB to be separated from the lower assembly.

The photos show the wiring up of the two PCBs as previously described, followed by the testing, and finally, actually running in the unit as a 3H. I still need a couple of minor adjustments, including adding a spot of weight for stability, and the paint colours are not yet right to match the Bachmann colours, but I feel like I am achieving something now.




















Forgive the clutter on the bench; that's due to some major rearrangements I have had to do recently, including building two new drawer sets and transferring stuff there, plus removing quite a bit of modelling stuff that had somehow found its way to other parts of the house and should not come into contact with two lively and mischievous kittens!

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[John ks]

Turns out I have a 4 CEP

 

So I did an exploratory operation

 

It looks like with this coach one wire (R LED-) goes straight through and is for the Headboard

The other wire for the interior lights has a branch on the PCB(printed circuit board) to control the lights in the coach

 

 

If my boards are the same as yours then:-

 

To link the top and bottom boards you only need 2 wires one from either VCC2 on the bottom to any VDD2 on the top board

Same with the GND 2 wire

 

If you want the coach lights on all the time then connect as per the top drawing

The orange wire is soldered to a GND connection which could be CND2 or if you feel confident to scrape the green off the circuit board and solder to there( see enlarged drawing)

Most of the circuit board is at GND potential, only the tracks aren't

 

If you would like the interior lights to work the same as the rest of the set then the bottom diagram should work

You will need an extra diode wired to diode D19 on the PCB as shown

 

 

As the components on this PCB are mostly SMDs(Surface Mounted Devices) soldering to them can be very fiddley

 

Hope this makes all makes sense

​John

 

 

 

 

 

[John ks]

Looks like while i was wrighting the last post you got it sorted

Although the buzzing sound is a bit disconcerting

 

The R LED- & I LED- are control lines from the decoder, the decoder effectively connects its function output to (-)

Looks like what you have done is connect that control line to the DCC  which could be very bad

Provided that you haven't cooked any components on the main PCB then reconnecting as shown in the previous post should make the buzzing go away

 

John

[SRman]

Thanks John. I'll have another look then ... maybe later in the week. your diagrams do make sense.

I'm happy that it is progressing, though, and there is light at the end of the tunnel on this project (pun not intended but it's there anyway!!)  

P.s. I really do appreciate the effort you have gone to with all the diagrams and helpful suggestions.

Edited August 8, 2017 by SRman