Hornby 395 blowing decoders

[reddragon]

The first DCC chip I fitted was to my Hornby class 395. I fitted it, run it backwards, then forwards, then pressed F0 and it stopped, dead chip!

 

OK, maybe as a newbie I messed up, so I took it to a train repair man at my local model shop. He tested the loco, found no defects and fitted a new chip. After a few runs, again whilst running power car first it stopped dead, lights & power off, but the dummy is fine with lights on.

 

Any ideas?

[dasatcopthorne]

Could the 395 be trying to draw too much current that the chip cannot cope with?

 

[reddragon]

I did wonder that, but the chip has a 1.5A rating, 2A max. The command unit didn't detect a short either.

 

[MarkK]

I'm not over familiar with the model, but would I be correct in saying it utilises two decoders?  Presumably one for motor power and lighting and the other for lighting alone.   Does the second decoder work the lights on  the dummy car only ?  

[reddragon]

1 hour ago, MarkK said:

I'm not over familiar with the model, but would I be correct in saying it utilises two decoders?  Presumably one for motor power and lighting and the other for lighting alone.   Does the second decoder work the lights on  the dummy car only ?  

 

There is a decoder in the dummy which works just the lights. The power car has fried 2 decoders so far. Both have the same ID.

Edited August 8, 2020 by reddragon

[MarkK]

You could try de-soldering the blue common and function wires from the decoder or 8 pin plug.  This would isolate the lighting circuit from the decoder and leave the motor power only.  You would have to risk another chip testing but it would confirm an issue on the function side.  

[dasatcopthorne]

Does it run OK on DC with socket blanks in place?

 

Then does it work with the decoders in and set to enable DC running.

 

Have you tried running just the decoder car on its own on DCC?

 

You need to eliminate things one by one to narrow it down. I think it is a problem in the train, not in the chips.

[dasatcopthorne]

Does the other chip burn out?

 

Could there be any connection between the two in any way?

 

[reddragon]

Everything was tested, running DC only was fine, power car alone failed on DCC 1st time and as a unit the 2nd time.

 

Time 1. Chip fitted to power car only. Ran alone on test OK, but no lights. Tried to turn on lights but when I pressed F0 it died.

 

Went to repair man who checked it on DC, then DCC and ran it for a while OK with dummy - lights OK. Brought it home and tested it as a 6-car unit and lights OK.

 

It is a pain to drive as deceleration is very slow to respond. After throttle is off, it continues on full power for 2 unit lengths before it starts to slow!

 

Time 2, first run on Roco Z21 ran out OK with power car at rear with lights on dummy. Return trip it just stopped dead.

 

The power & dummy have no links other than via the track. The dummy chip is fine. No shorts were detected by the command unit.

 

The lights do seem to be an issue on DCC - any ideas how? My repair man is at a loss.

 

 

[smokebox]

18 hours ago, reddragon said:

I did wonder that, but the chip has a 1.5A rating, 2A max. The command unit didn't detect a short either.

 

What chip are you using?

[34theletterbetweenB&D]

6 hours ago, dasatcopthorne said:

...You need to eliminate things one by one to narrow it down. I think it is a problem in the train, not in the chips.

Pound to penny there's a bridged connection either in the decoder socket or elsewhere in the circuits on the mechanism, and track power is connected to a decoder output.

 

The suggestion @dasatcopthorne makes is one good way, or you can go for the @34theletterbetweenB&D 'total impatience method'  of rip out the socket and any board it is mounted on, test that there is  full isolation of motor and all light connections from track supply, and then hardwire the decoder.

[dasatcopthorne]

You've narrowed it down the the lights somehow.

 

Take the power car (only) and disconnect the lights as near the chip outputs as possible. Re-check running.

 

I feel that there must be a connection of some kind between the lights circuit and other chip inputs/outputs.

 

Dave.

Edited August 9, 2020 by dasatcopthorne
spelling

[RAF96]

Is it the earlier non DCC Ready Blue Rapier or the several later DCC Ready versions with a socket, as the pcbs are totally different in these variants.

 

I suspect a short on the socket if DCC Ready or an overload of the function outputs if not.

[reddragon]

41 minutes ago, RAF96 said:

Is it the earlier non DCC Ready Blue Rapier or the several later DCC Ready versions with a socket, as the pcbs are totally different in these variants.

 

I suspect a short on the socket if DCC Ready or an overload of the function outputs if not.

 

DCC ready, I just used the 8 pin plug

[MarkK]

If you have a multi meter you could check for shorts at the 8 pin socket.  With the engine off the track and the meter set to continuity or an appropriate resistance setting probe the yellow, green, white and blue pins in turn.   Ideally there should be no resistance between them.  Then check each of these wires in turn with the red, black, orange and grey pins.  Again there should be no resistance between them.   A short on the socket would be easy to remedy.  

 

Hope this helps

[reddragon]

I'm going to hard wire in a decoder & remove the socket.

[MarkK]

Good luck, let us know how you get on.

 

Mark