Tcs cn decoder in analog mode question

[daniel_leavitt2000]

I just finished my first TCS CN decoder installation in a kit bashed GP20 that uses a LL Canada GP9 chop nose chassis. The space in the cab end was very limited so I had to install the decoder backwards - the "chip" end being in the rear rather than the front.

While I was able to reprogram the DCC functions to operate normally, the engine still runs backwards in DC mode. Switching the wires to the motor won't help, because the built in LED would still operate in the opposite direction.

Is there a CV that would reverse engine direction in DC mode?

FWIW, I now "get" why people like TCS so much. Programming is simple and straight forward. It runs tie to tie out of the box. I can get my NCE decoders to work as well, but it takes a lot of trial and error during programming which can take up to 40 minutes each for them to set up.

[C855B]

Nope, no CV for that. Your problem is entirely from installing the decoder backwards. It relies on the frame orientation to be "normal" for DC. I have a fleet of "Classic" GP35s and if it wasn't for the GP-CN they would probably have been bench queens for the remainder of their days.

[daniel_leavitt2000]

Eh, I was afraid of that. I'll just deprogram DC mode then.

How do decoders handle DC? Is it a chip bypass and pass though? Or is there any active work being done by the decoder?

[Jbub]

Nope, no CV for that. Your problem is entirely from installing the decoder backwards. It relies on the frame orientation to be "normal" for DC. I have a fleet of "Classic" GP35s and if it wasn't for the GP-CN they would probably have been bench queens for the remainder of their days.

Can the chip section of the decoder be installed "upside down" in the rear slot of the frame? That would reverse the polarity and fix the problem in DC. I have a pair of LL gp60s with the similar frame I'll be putting a loksound micro in.

[C855B]

Can the chip section of the decoder be installed "upside down" in the rear slot of the frame? That would reverse the polarity and fix the problem in DC. ...

Not a bad idea, it may work if it still fits. You'd have to flip BOTH halves, however.

As to the "DC pass-through", I don't know for sure. What I can surmise is because the ability to respond to DC varies so much between decoder brands there has to be some manner of proprietary voodoo involved, so I'd guess there is some active element in the middle.

[Jbub]

Not a bad idea, it may work if it still fits. You'd have to flip BOTH halves, however.

As to the "DC pass-through", I don't know for sure. What I can surmise is because the ability to respond to DC varies so much between decoder brands there has to be some manner of proprietary voodoo involved, so I'd guess there is some active element in the middle.

I guess directional lighting would be wrong also.

[C855B]

I think the directional lighting would then be fixed. By flipping them over with the boards backwards in the frame you get a double-negative, something that's topically current.   Seriously, the main challenge with that is whether the components normally on top will clear the frame.

Thank you, Daniel. "For what?" he queries. For making me think seriously about the CN-GP and fitment. There's a back story.

Over the past, oh, I dunno, two decades I have been collecting the early non-DCC Kato SD45s whenever I find them on a bargain table at a train show or swap meet. These are incredibly sweet runners if you ignore the top speed problem. Equally important, the SD45 was my "first love" after an article and plans in a 1966 Model Railroader. SP also started running them in 1966, so I was trackside when they were new, and many times experienced the incredible booming bass a lashup of the V20s would setup in the confines of the valleys around Tehachapi. That's an SP SD45 in my avatar. So, big emotional attachment to the 45. So about the CN-GP...

I have accumulated probably a dozen or more of the Kato version, all waiting for the roundtuit to hardwire DCC. I never gave a second thought to the CN-GP for anything other than GP20s and GP35s in the fleet. Well, I stumbled into a couple of factory-fresh Kato SD45s in a storage box this evening while looking for something else, and given our chat today about the CN-GP wondered out loud "Will it work in the old 45?"

Answer? Damn tootin' it does! Drill a couple of holes to get the grey and orange wires to the brush holders, rout a channel for the gray wire, do a little trimming of the frame front and back to clear board parts, and voilà!!!. LEDs are even in the right places for the headlights when everything is done. Programmed-up with no problem and tamed the top speed in one shot with mid and max motor settings. I was so pumped about it working so easily and running so well I retrofit the new, finer Kato wheelsets, painted the trucks aluminum (UP, of course), installed TSC, and it's now in the running fleet on the layout.

One down, eleven.. or so... more to go. Obviously I'll have to add renumbering to the finish tasks.

A "bucket list" item checked off! Again, thanks! 

[daniel_leavitt2000]

I tried flipping the boards last night and it won't work. The rear (technically the front) board has the orange motor wire too close to the contact plate, and interfere with the board resting on the frame.