Installing a TCS KA3 or KA4 on an LM-3S without a bridge rectifer

[G8B4Life]

RP doesn't get its control signal from the rails.

In DCC mode it does (using a DCC controller such as NCE, DigiTrax, etc) which is what I believe Bill is talking about. In that case I suspect the bridge rectifier will most likely prevent use in DCC mode, as it will prevent the DCC signal from reaching the LM which has the smarts to decode the signal at it's own internal rectifier.

The CI-1 doesn't output DCC, only RP.

- Tim

[Alan]

Well, something is amiss. The LM2 I opened up has the track wires going directly to the rectifier diodes. No way a DCC signal is going to get through those.

Easy enough test. Will a RP equipped loco operate on a DCC layout without a HC or CI in the house?

[G8B4Life]

Easy enough test. Will a RP equipped loco operate on a DCC layout without a HC or CI in the house?

Most certainly (though there was a HC and CI-1 in the house). I was operating two of them with my NCE PowerCab yesterday testing the consist problem when using NCE with the LM in DCC mode. The HC and CI-1weren't in use at all, all operation was done by the NCE PowerCab. Only the LM's are dual mode RP and DCC. The HC and CI-1 are strictly RP only.

I figure that there is no component available that could take a DCC waveform directly as it's power so it must be rectified first so I'm guessing that the LM (and DCC decoders) have some sort of smarts to decode what's being seen by the internal bridge, though I've got no idea how; that's way beyond my electrical knowledge.

- Tim

[Alan]

I have another S-2 installation to do soon. Fitting the LM inside the very narrow hood of a S-2 requires removing the LM plastic case. I'll take a close look to see if there is a board trace connecting to the AC side of the bridge. By your observation there has to be. I must have overlooked it last time I stripped a plastic case.

Back to the original question... I think we are safe in saying an external KA bridge will definitely block the DCC signal.

[KPack]

Back to the original question... I think we are safe in saying an external KA bridge will definitely block the DCC signal.

It does indeed block the DCC signal.  I confirmed while testing on my friend's layout.  This would be an issue with the LM-2S only as far as I know, as the LM-3S can be hooked directly up to a KA.

-Kevin