N Gauge Forum

Your Layout and Models => DCC => Topic started by: Yet_Another on March 13, 2018, 10:16:01 pm

Title: DCX76 odd behaviour - lights on
Post by: Yet_Another on March 13, 2018, 10:16:01 pm
I have just encountered some odd behaviour from a Graham Farish class 25 fitted with a CT DCX76. As soon as I put the loco on the track, the lights come on in the forward direction, and are not 'turn-offable'. If I turn the lights on, and change direction to reverse, ALL the lights, tail and head are on in both directions.

No problem, thinks I, just do a hard reset. So I set CV1 to 0, as the instructions state. This does reset lots of things, including the address and CV29, but doesn't fix the light problem.

Perhaps it's the hardware, then. So I took out the decoder & popped in a Bachmann one. The lights work as expected in the loco, so nothing wrong with the circuit board/wiring.

I put the DCX76 back in, and it's still whacky. The loco drives OK, I can set the address & CV29 values OK, but I don't seem to be able to do anything about the lights.

Does anyone have any experience of this sort of thing?

I should say that the other class 25 & a class 24 that are both also using DCX76s appeared to be absolutely fine, so as far as I can tell, it has to be the decoder.
Title: Re: DCX76 odd behaviour - lights on
Post by: dannyboy on March 13, 2018, 11:05:13 pm
Does the fault replicate itself if you swap the 'faulty' chip with a good one from, say, the Class 24? If so, then it must be the chip, if not ....?
Title: Re: DCX76 odd behaviour - lights on
Post by: Yet_Another on March 13, 2018, 11:26:46 pm
Does the fault replicate itself if you swap the 'faulty' chip with a good one from, say, the Class 24? If so, then it must be the chip, if not ....?
As I said, I swapped the decoder for a new Bachmann one, and the Bachmann one worked fine, so it's definitely something in the CT decoder that's gone awry.
Title: Re: DCX76 odd behaviour - lights on
Post by: dannyboy on March 13, 2018, 11:29:39 pm
I was just wondering if you put the 'faulty' decoder in one of the other loco's does the fault occur in the other loco?
Title: Re: DCX76 odd behaviour - lights on
Post by: Yet_Another on March 14, 2018, 10:11:53 am
Oh, I see what youíre saying. Iíll try that this evening.
Title: Re: DCX76 odd behaviour - lights on
Post by: Only Me on March 14, 2018, 12:10:12 pm
That means chip upside down... I think
Title: Re: DCX76 odd behaviour - lights on
Post by: Yet_Another on March 14, 2018, 11:57:00 pm
OK, further testing this evening, while not reading the forum.

Using a class 24 & another class 25, both with the same DCX76 as the problem one, I swapped both ways, and in all cases, the problem decoder remained the problem decoder, irrespective of which loco it was in, and the other decoder/loco combinations worked fine with no untoward effects. The orientation of the decoders was kept the same in all cases, so it's not an 'upside down' problem (also, I could read the CVs, which I don't think you can do if it's in upside down).

Some further observations on the symptoms:

The 'permanently on' lights are dimmer than the normal lighting, and flicker in unison. They seem to dim further when the normal lights are turned on in the opposite direction, and the lights are the normal brightness when running in the 'same' direction.

Also, at one point, when in the class 24, it became very jerky and uncontrollable for a short period, but only for that short period. Otherwise, it seems to be fine as far as motor control is concerned.

I'm starting to think that this might be a wet Sunday afternoon, record all the CV settings exercise, and compare & contrast with a working one. Or it's just broken.
Title: Re: DCX76 odd behaviour - lights on
Post by: dannyboy on March 15, 2018, 12:03:32 am
I am a novice at DCC - if I have a DCC fitted loco' and it does what it should, I am happy. It certainly sounds to me, from what you have written above, that the decoder is faulty. Whether it is something that can be rectified I know not, but I am sure some of the more DCC knowledgeable people on the forum will know. Good luck in sorting it out.
Title: Re: DCX76 odd behaviour - lights on
Post by: NinOz on March 15, 2018, 05:09:14 am
For me at this point it is a faulty decoder, so it would be check for something easy to fix (solder shorts on decoder especially the pins), or bin, or send for repair or replacement.
Title: Re: DCX76 odd behaviour - lights on
Post by: Izzy on March 15, 2018, 08:51:08 am
Really does seem to be faulty and needing replacement.

Izzy
Title: Re: DCX76 odd behaviour - lights on
Post by: Yet_Another on March 28, 2018, 08:42:49 pm
Quick last word on this.

I spoke to Digitrains, just for advice, really. They advised that I send back the decoder, so I did, and the replacement was put in the post by return.

Top marks to Digitrains!
Title: Re: DCX76 odd behaviour - lights on
Post by: bmwm4rkym4rk on March 30, 2018, 11:24:15 pm
Yes I have also found being a dcc installer there has been some issues with mainpy the dcx77 range where they keep blowing so much so a major stockist has stopped using them