Uni-directional issues with Lima Class 20 (TTS decoder fitted)

[Deem]

I bought a second hand Lima Class 20 which have been fitted with Hornby TTS 8 pin decoder by previous owner.

Issue's I am having:

Loco will run in both direction if Driver cab is toward the rear, if I turn the Loco around (driver at the front) it will not work in DCC but in DC mode it will work.

I have reset the decoder by setting CV 8 Value 8. Try to program few times to see if I can fix the issue without any success.

Once the Loco (with driver cab towards the rear) is programmed Loco will run opposite direction according to Controller direction.

I try changing the CV 29 to 7 but loco still run opposite direction instead of intended direction as per the controller.

Try the CV 28 with Value 6 but still no success.

My main issue is or what I don't understand why won't loco run or be programmed when facing the driver cab towards front, once I put the Loco with cabin side towards the rear Loco will run and I can do the programming.

Thanks in advance

[Rog RJ]

Sounds rather like the original TTS decoder fault. When the TTS decoders were first released they had this fault where they had to be facing a certain direction to be programmed or run correctly. They had to be returned to Hornby for re- programming.

[Deem]

In DCC mode Loco will only works in this position.

[Deem]

If I change the position to Driver cab on the front (opposite to this position) it will not work in DCC mode

[Deem]

In this picture direction if going forward but loco will run opposite, when direction changed on controller Loco will only run opposite to controller direction.

[Fishmanoz]

Agree with Rog - you have an old TTS with the firmware bug. Contact Hornby for a returns number.

[Deem]

Hello and Thanks for everyone's input, because this was something totally new to me, I thought I try few Loco to see if changing reverse position how does Loco perform.

I don't know if this correct way the Loco's working or I have number of faulty Decoders.

I would appreciate any input,

I tried Hornby R3171 P2 Coke O North, which I tried and notice that When I turn the position of the LOCO ( so if I am looking at the Loco in front of me tender side is on the left side and front steam end is on the right) Loco run in both direction fine but it will run opposite direction as oppose to Controller direction. Once I turn the Loco around and everything will work as they suppose to work.

Same thing I notice with Hornby R3784 Class 66 when I change the position on the track from Driver side to my right when I am looking at the Loco, Loco will in both direction but Loco will run opposite direction instead of what controller is showing. Once I turn the Loco around, everything will work as they suppose to work.

If my understanding is correct DCC runs in AC voltage instead of DC voltage so it shouldn't make any difference what position Loco is sitting on track.

Regards

[Fishmanoz]

You are correct Deem, a DCC decoder has no idea which way it is placed on the track if working correctly. The exception is the batch of TTS decoders with the firmware bug from some years ago. These need to be returned to Hornby for firmware fix.

But note, the DCC track voltage is not AC although it does behave something like AC. It is correctly called a bistatic square wave whereas AC is sinusoidal.

The difference becomes a obvious when you look at it in the “frequency domain” as opposed to the time domain (plot signal amplitude against frequency on the ‘x’ axis whereas time domain plots amplitude against time on the ‘x’ axis). AC gives you a single vertical line at the signal frequency whereas a square wave gives you a whole family of vertical lines being the fundamental frequency of the signal plus in decreasing amplitude all of the harmonics of that signal. Then when you encode the DCC commands onto it, the whole family jumps up and down the ‘x’ axis as the fundamental frequency of a ‘1’ is different to that of a ‘0’. More than enough said.

[96RAF]

Have a read of this Deem . . . https://dccwiki.com/DCC_Tutorial_(Power)

. . . especially the second para of Multi-function decoders which explains why this uni-directional bug can happen if the decoder is faulty.

[Deem]

Thanks for everyone's input and explanation.

I am assuming much older Hornby Decoder's (2 of them - one in Lima Class 20 and second in Hornby Class 66) are faulty and I will contact Hornby on Monday to see if they could help to reset the Decoder.

LiasDCC decoder's I bought and been using in Hornby P2 Coke O North was bought about 6 months ago so maybe they are or aren't faulty? As steam loco are easy to tell in which direction to be used I have been using them in correct direction and never came across the issue until I bought above second-hand loco with older decoder's, which made me realise how to test further. Now all 3 of my Loco which aren't in storage are not behaving correctly. 2 Older decoders and 1 LiasDCC decoder in P2, all are behaving very weird.

Any thoughts?

[Deem]

Another Twist,

Recently I bought a decoder from Lendon of Cardiff (X11485 Tornado TTS) which I install in the Class 20 just to test: it doesn't matter in which direction the Loco is placed on track, Loco will run correctly as per the direction of Controller, I swap the wiring but it didn't made any difference because Loco ran in correct way what ever controller instructed the Loco.

So my thoughts are Older Hornby decoder are definitely faulty but LiasDCC are faulty as well.

I will investigate further and update tomorrow.

Regards

[Deem]

Update:

I spoke to Hornby today and try to explain to advisor the issue I am having, he wasn't aware that if it is possible to reprogram the Decoder. Asked me to send email to

technicalservices.uk@hornby.com

explaining everything and they will look into my problem.

Regards

[Fishmanoz]

Rob, sounds like your intervention here might be needed. Our corporate memory on such things is clearly longer than Hornby’s.

PS. Every time I read this title, the pedant in me bristles, for 2 reasons:

• apostrophe man strikes again - see hanging possessive case on issues
• why say you have “weird” issues when you could have just as easily and more informatively said what those issues are (TTS only works when placed on the track one way)

[96RAF]

@Fishy

How about the title now.

I have flagged the tech guys to expect contact, but I thought their Repairs Dept had the kit to fettle the decoder.

[ColinB]

I am surprised that the TTS decoder actually works in an old Lima loco, when I was doing tests on my class 66 to measure the motor current to fit a TTS decoder, it was greater than the maximum value for a TTS decoder. I don't know though whether the Lima class 20 uses that old pancake motor that is fitted to the class 66.

[Deem]

Thanks for changing the title 96RAF.

Also thanks for your help informing Tech Dept.

ColinB am I am new to this hobby and still learning all the terms, I will upload the picture of the motor and maybe you guys can teach me what the term for this type of motor.

Motor in this particular loco is mounted sort of in the middle and drive the front bogie via a drive shaft.

Regards

[96RAF]

Only valid service sheet is non sound 335 showing a cardan shaft from a can motor to the bogie.

There is a sound version listed SS340 but the link leads to an old 21-pin Class 60.

My Class 20 runs fine with a fettled TTS decoder.

Hornby tech says to arrange a return to get the decoder fixed.

[ColinB]

When I measured the maximum current on my Lima class 66 it was 700 milliamps, which is higher than the maximum current of a TTS decoder. I must admit I wasn't brave enough to actually try one, too many of mine had died without doing anything wrong. It may be that as the class 20 is smaller it draws less current. In the end I bought the later Hornby class 66 chassis and corresponding bogies, which draw far less current, meaning I could use a TTS decoder.

[Deem]

[Deem]

Bit messy Job compare to 96RAF class 20 but that's how I received it, hopefully once all sorted and Loco run as they suppose to run without any directional issue or opposite running instead of what controller is instructing the loco.

I am waiting anxiously for Hornby Tech to advice on how to send the Decoder and i will post it. But I have not heard anything from them.

Thanks again 96RAF

[Deem]

Further Update:

I bought Brand New J36 Maude TTS decoder from Hornby Directly Class Q1 (as Hornby don't make Q1 TTS so this was the closest I could install), installed the decoder and as I was testing I noticed,

When Loco is in Front of me - tender on my right side and steam boiler on my left, all works fine as it suppose;

Sounds works fine

Loco follow all command as directed by Controller.

But when I turn the Loco around (Boiler on my right side and tender on the left side) all works fine except directional running is opposite of what controller showing or instructing the Loco.

I made the video and I am going to upload to GDrive and hopefully will be able to share with you all.

[96RAF]

If I understand it right when the loco is facing left and the controller is directing fwd the loco goes left.

When you turn the loco round to face right, are you expecting it to go right (fwds) when the controller is showing right. If so you have not locked onto the fact DCC sees direction fwd as loco forward, therefore if your controller fwd shows the arrow facing left then that is the direction it is commanding.

Not very well explained - too early in the morning, so try this:

Loco facing left and controller showing left (if that is your fwd). Loco goes forward.

Loco facing right and controller the same as before showing left (your fwd). Loco goes forward. That is correct. In DCC the controller fwd is loco front going forward regardless of the way round it is on track as you are controlling the loco direction not the track direction.

[Brew Man]

Yes, it sounds to me that Deem is misunderstanding how DCC works.

[Deem]

Thanks for your input, 96RAF and Brew Man.

Maybe I am not explaining myself clearly, apologies for that, I am going to try one more time.

2 separate issue's.

Lima Class 20 with Hornby TTS have problem, so I am going to leave this aside and wait for Hornby Technical services to come back to me.

As for DCC system, how that works or what direction the Locomotives should travel when commanded by the controller.

I am new to this hobby, specially the DCC part. So I am learning as I am coming across any issue's and getting help from my Fellow Modeller in this Forum.

My layout is small with maybe 1 Meter with 3 lines connected with points. So I am sitting at my table trying to test or have some fun.

The way I use my layout is my left is the forward with all loco's and my right is the backward.

So if I place any steam loco, boiler side is front and on my left, tender is rear and on my right.

In this position everything works fine in DCC.

Now if I swapped the loco on track, boiler on right and tender on left, everything still works, sound and forward and backward. Only issue is Controller showing right arrow on screen but loco is going left, when changed the direction button on controller and now controller is showing left arrow on screen but loco is going right.

IS THIS NORMAL? or something is wrong.

[Deem]