TTS Decoder and track polarity

[Andrew Yates1707820370]

I have acquired 2 class 43 TTS decoders and fitted them to locomotives. When placed in one direction on either the programming track or main, they work correctly; but if the locomotives are turned round, they cannot be addressed and do no respond to the controller (Z21).

I already have TTS class 40 and 47s, but they work fully in both directions.

Has anyone else experienced this?

[Howbi]

Hi Andrew, welcome to the Forum........that's a strange one......as your other locos work correctly then there is no issue with your track or controller.........can only suggest you unplug the 2 offending TTS decoders and turn them round in their sockets...........sometimes it is difficult to identify pin 1 for the orange wire pin to fit into.........HB

 

ps.......track polarity is not an issue in DCC decoders as it is a form of AC current.

[2e0dtoeric]

Are you turning the track power OFF before turning the loco's?

If not, the decoders might be getting confused, and seeing the interrupt as a noise spike, and turning themselves off until you re-start the controller.

[Phil_Spiegel.]

My usual first question is - Did you check with a Multimeter before installing the decoder?      If not, why not?  Multimeters can be bought for less than than the cost of the cheapest Hornby Decoder (the 4-wire version fo the Sentinel). Using one, eliminates the standard basic fitting problems and might show up an unspotted diode....

You give no clue as to the locos you have fitted them into - one  could guess at an unfitted  Class 43 - old Lima, old Hornby, new Hornby , or latest Hornby 8-)   SOME of those had bulb lightng - others have LEDs - have you checked whether the problem occurs when the lighting is disconnected ??? - the LEDs involve diodes, and if not wired in correctly could possibly account for a difference depending on direction.

You may have read of the 'fun' I have had with a couple of pairs of TTS from Virgin EC HSTS ... was this your source too???   Mine 'recovered' after days left without power.  The problem also 'occured' when sparks were also observed as it as placed on the track - suggesting charging of capacitors as a potential problem, and that I was 'hesitant/inteittant as I placed then on the plain track. .... Do they need better 'inrush' protection ???.

IF THE PROBLEM ONLY OCCURED during 'programing' then this (  with accessory decoders of various makes) - is a known / considered acceptable situation because the normal 'symmetric' rules don't apply during programming ... - but should NEVER affect a 'Mobile' device?.   . if you find an accessory device does not program (in CV prog mode)  when wired one-way - it is worth swapping the dcc wires over, and finding they then program.

[walkingthedog]

Phil you asked ' Did you check with a Multimeter before installing the decoder?'.  The question is did he check what. Not everybody knows what to do with a multimeter let alone what you are looking for. What setting, where do you touch the probes, what readings are you looking for?  😆

[Howbi]

I have installed 30 to 35 decoders over past 6 yrs never once thought I would need to use a multimeter first.......as WTD said, to check what?...........HB

[Andrew Yates1707820370]

I wrote a reply but it appears to have been lost in the ether. Suffice to say, everything has been tested by a multimeter. The decoders have been tried hard-wired in an old Lima HST and plugged into a Heljan chassis. The results are the same. The old HST has the lights disconnected, but the lights on the Heljan chassis work ok, so the plug is in the right way round.

I don't think it's a charging capacitor issue as the locos can be turned round and back, with the same effect.

Phil - I would like to know more about your issues with the ex Virgin decoders, as I suspect that these are from that source.

Thanks again

[mjb1961]

Hi,,,,,As a guess these two class 43 TTS have probably came out of one of hornbys HST,s which have two power cars ,one at each end ,now the thing that gets me thinking is that the decoders need to be set up correctly because one power car will be running in forward but the other will be running in reverse and vice versa ,this is my way of thinking anyway ,I may be totally wrong but it may be something worth thinking about ,,try resetting both decoders ,,,,someone else on here will know what the problem is I'm sure ,,,,Chrissaff ,comes to mind !!!!,,,,mjb

[Chrissaf]

Sorry, can't help on this occasion........a decoder only allowing a loco to run in one direction only is not something I have had to deal with before. Although I do have a vague recollection of seeing something similar to this being reported before. But the recollection is very vague, and I don't recall reading a fix for it either.

.

Chrissaf

.

PS - When experiencing strange operational phenomena, I would always suggest doing a factory reset of the decoder(s) [write value 8 to CV8] first, before trying other things.

[Rog RJ]

I'm fairly sure this problem, or something very similar, has been reported in the dim and distant past.  IIRC it was something like the wheel pickups needing adjustment, not something that you would think could cause it.

[96RAF]

@phill

 

I am interested in your statement that the normal symmetrical rules do not apply to accessory decoders. Can you please tell more.

Rob

[Blackbird]

Hi, I have a reasonable understanding of electrical and electronic systems and considered that DCC had no 'polarity'. Wiring was designated as 'A' and 'B' to avoid cross connection and short circuit. The decoder determined the direction of travel of the loco, so the loco would always travel 'forward' whichever way it was placed on the track. the same rules would also apply to accessory decoders. Basically the decoder, whether loco or accessory would have no 'knowledge' of the DCC connection, (polarity?)

[Fishmanoz]

That description I can relate to Blackbird. The DCC signal on each track is almost the same, the difference is they are 180 degrees out of phase with each other. If you look at the tracks individually, they appear the same, but if you look at them together in time, then one is heading positive when the other is heading negative. Hence the short if you connect them together. 

 

And i agree, you turn a loco around on the track and the loco decoder sees no difference. Similarly, swap an accessory decoder's track connections and again, it sees no difference. 

 

So the only reason I can see for the loco behaving differently depending on which direction it is placed on the track is something mechanical with the wheels and pickups.