Odd decoder issue

[Trip]

I've bought a Hornby R3390 from ebay It's had the sound decoder(s) remove and left with an 8-pin socket in both the powered and dummy car.

 

Fitting a decoder to the powered car worked fine. Fitting a decoder to the dummy car (to work the lights) and I can't get a response from the decoder on the programming track. Using a multimeter in beep mode I've established that there is a perfect connection from the rails all the way to pins 8 and 4. (This is measured at the solder contact of the wire that runs to the decoder.)

 

The decoder was pulled from another loco which was working fine.

 

I'm assuming that although the other connections to the decoder are important for working the lights the only connections required to read/write CVs are pins 4 and 8 to the tracks? 

 

Any ideas what could be wrong?

[soony]

You need to have a 'motor' connected to get a programming response.. alternatively plug it in the power car , program it,  change CV29 to give it reverese ( the power car goes forward and the trailer goes backwards at the same time) , then put it back into the trailer car and  finally program the decoder now in the power car...  alternatively put the trailer chip in any handy 8 pin DCC  loco sitting around and program it there ...

[Trip]

That worked. Thanks very much gents.

 

If anyone knows why a motor must be present to get a response (or even read CVs) I'd be very interested to know.

[Pete the Elaner]

Program both together on the programming track

That would be my preferred method, but it may leave the lights on in the wrong direction on 1 of the models, in which case, I would set the direction as per the dummy, so the power car is now wrong. Remove the dummy & set the direction to forward in the power car.

[NIK]

That worked. Thanks very much gents.

 

If anyone knows why a motor must be present to get a response (or even read CVs) I'd be very interested to know.

 

Hi,

 

DCC loco decoders normally use pulsing of the motor in order to communicate data back to the command station during programming on the programming track.

 

The command station can read the data by measuring the changes in current drawn.

 

 

It saves the decoder manufacturer having to add a resistor and an electronic switch across the DCC inputs to the decoder.

 

Regards

 

Nick