Revisiting an old question... MD mXion decoder into an older LGB Railbus...?

Zerogee

Clencher's Bogleman
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Hoping that somebody with actual hands-on experience of the conversion can help with this, please...?
I know there are a couple of old threads on the same question (at least one of them my own), but I'm now finally at the point where I'm going to attempt one of these and I've run into a specific problem with the wiring for the lights.

The model is an LGB Wismar railbus (the "pigsnout") from the late '80s or early '90s; the decoder to be fitted is one of MD mXion's SB boards, made as a specific drop-in replacement for the old PCB in the model.
My problem is understanding the connections and rewiring required for the front and rear lights - the two little PCBs that are located inside each end of the railbus body, each with a red and a white 5v bulb, to give the directional white headlights and red taillights depending on direction of travel.

The much larger PCB in the roof, which carries the interior lights and cab lights, is quite straightforward and details of the required modifications for that are clearly shown in the MD decoder manual; however the little end boards shown in the manual are only for a later (2000-ish) model, where each lighting board has a three-wire connection (white, brown, green) to the main PCB.

The earlier model differs from this in that the wiring to each light board is only two wires, red and black... can anyone who has actually done one of these (and maybe taken notes and/or photos?) tell me exactly how the red and black wires from the front and rear lighting boards should be connected to the new mXion SB decoder, and also if the modification to the light boards (a jumper wire between two PCB tracks) is the same as for the later three-wire type shown in the manual?

Sadly the video on MD's site about installing an SB board isn't any help either, because that shows an even newer version with all the lighting connected using LGB's really useful black/black/black/black cables... :D

Thanks in advance for any practical advice that can solve the problem!
Jon.
 
Supplementary question on same subject... when modifying the little end lighting boards, should all of the tiny components (diodes??) on the original boards be cut off?

Jon.
 
When I did my I think similar aged one I cut differing lines into the circuit board to revise the routing of power and lighting. Please do not ask me anymore from my link as it is long forgotten!
 
Thanks JonD - my problem is figuring how (and where) to make the connections to the MD board, so I really need someone who has already done exactly the same install....?

Jon.

Martin - thanks, just replied to your PM...
 
Thanks JonD - my problem is figuring how (and where) to make the connections to the MD board, so I really need someone who has already done exactly the same install....?

Jon.

Martin - thanks, just replied to your PM...
The board has holes where the 4 metal uprights (between the seats) pass power from the chassis into the roof mounted board. Understanding where these come from on the chassis and where they go to in the board should help you understand. It may be that 2 go from each track source and you should be able to follow that through the separations in the biard.
 
The original board has 'brass' inserts that the poles up to the roof-board plug into..

The bits I was supplied with included four plastic 'straws' (think the extension on a can or contact cleaner, or WD40).
The boards I have had in the past did not have these 'sockets' for the rails to connect. - Just plain holes in the board.

Hence I fed wires up them, and rearranged how the roof lighting functioned.

PhilP.
 
Reposting with his permission, here's what PhilP told me in a PM; it seems to answer my specific question, and hopefully will also be useful to anyone else considering the same task....

Text in RED is my edits/additions...

............

Phil's bit:

You will need an extra wire from the lighting board.
You can (should) remove the diode(s) and all other original discrete components from the boards.

I would use a blue wire, as this will be Decoder +ve. And will go to the common connection on the lighting board between the two bulbs.

I would move the Red wire to connect to the red bulb, and the White wire to connect to the 'white' (clear) bulb.

The Blue wire from each end will connect to Decoder +ve.
The White wire front the front and the Red wire from the rear will connect to to the Front light output.
The Red wire from the front and the White wire from the rear will connect to the Rear light output.

**Check the lighting output voltage divider setting is right for 5V bulbs BEFORE connecting the lamps or power. (According to the MD manual for the decoder, the lighting outputs are all regulated at 5v as supplied - still, no harm at all in double checking!)

End of Phil's bit.

............

I think I now understand how the setup actually works... it can take me a while to really get my head around some things, I blame advancing age... :D

I've now just got to work out how to make the actual connections at the decoder end - I'm reasonably comfortable with general soldering, attaching wires etc, but very shaky (sometimes literally) on the sort of very fine work required with soldering directly to decoders and other electronics - where a slip of the iron can be very expensive; thus I prefer connections where I DON'T have to solder anything to the decoder board itself.
Therefore I will be trying to make all the connections to/with the four metal stanchions/handrails as discussed above - these don't carry track power at all, they are connected (not necessarily in this order) to the following decoder in/outputs: Light V (Vor = front), Light H (Hintern = rear), Decoder +5v, and function output A3 (Interior Lights).

Jon.
 
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