Mallard R2784X 'DCC Ready' retro fitting TTS decoder.

[Chrissaf]

My first post but been a Hornby man for many years - so be kind to me.

I have successfully fitted the TTS decoders to my Duke of Gloucester DCC Ready with the speaker fitted in the tender together with front and rear lights. This was a great success so I ventured onto the Mallard R2784X to fit another TTS decoder.

I fitted front lights to the loco and rear lights to the tender and tested - all was O.K.

I proceeded to fit the speaker into the tender which has a Dummy Ringfield Drive Unit [X9828] and placed the TTS speaker against the RHS of the Dummy Ringfield Drive Unit [X9828] with the speaker terminals facing outwards against the plastic wall of the tender. I held the speaker against the Dummy Ringfield Drive Unit [X9828] with double sided tape and wired the speaker to the TTS decoder using the the same original wire connections but lenghtened and the joins heat shrink wrapped. The plastic tender cover fitted very neatly over the tender chassis.

Thus the speaker wires ran from the tender to the Locomotive DCC pin socket.

Then tested the sound via placing the locomotive on my DCC layout with the tender not connected to the locomotive & clearly off the layout out of electrical current, only connected directly with the speaker wiring and WHAM - theTTS decoder sizzled. 

I checked all my wiring for short circuits with a multimeter etc. etc. and replaced the TTS with a new one again and WHAM - another burnt out TTS decoder!!!

So I got out my multimeter and cut the speaker wires [thus no electrical current feed], removed the tender to my work table away from my layout and tested the speaker for a short or open curcuit and found to my surprise that whilst the speaker was adheared to the Dummy Ringfield Drive Unit [X9828] the multimeater readings were highly fluctating but when I removed the speaker from the tender and re-tested it all was correct. 

So I replaced the speaker, unconnected from electrical wiring,against the Dummy Ringfield Drive Unit [X9828] and the multimeater reading were highly fluctating again.

So is it possible the the electrical current feed of 1amp to the speaker when origionally hooked up to the TTS decoder and switched on, had a amp increase caused by the configeration of the Dummy Ringfield Drive Unit [X9828] CONTACTS and the magnet field in the speaker???

The tender circular contact configeration, even though not powered,the speaker may operate on the principle of how a permanent magnet will attract and repel an electromagnet due to the tender circular contact configeration???

Any help would be greatly appreciated with this problem

 

[walkingthedog]

Out of intetest how many lights did you fit to the front and to the back of the loco?

 

Do you have a picture.

[ColinB]

I have found out the favorite for blowing up Hornby DCC Sound decoders is if one of the speaker wires accidently touches the loco chassis. If can easily do it, especially if one of the speaker connections is connected internally to the speaker chassis. As your tender obviously has a lot of metal in it, are you sure you didn't accidently do that, you wouldn't notice it happens in less than a second. You generally don't know you have even done it. I have got exactly the same loco, that I added two forward lights and a smokebox glow. The big difference is that I bought a small speaker off YouChoos and mounted in the loco itself, this avoids having any wires going to the tender and lessens the risk. I like theirs because if you buy the one with the sound box, the bottom is completely plastic,. You can stick this side to the loco chassis with double sided sticky tape and the connections are at the top which you can easily cover with tape. I am assuming with the lamps you used suitable resistors (1 Kohm  or greater). I have found from bitter experience insulate everything, try to not have any flayling leads, those cheap mones from EBay have an unconnected stay alive wires which can accidently "short out", and doublr check that speker wires and motor wires do not have a connection to track voltage (usually caused by stray strands of wire). The biggest issue is putting the electronics in a small space and while you put the body on, it moves and touches something.

I have wondered if the extra metal would have an effect on the speaker as I did have an issue with another Hornby DCC sound module on my West Country that failed after a week, this was where there was a big lump of metal right underneath the speaker  (I retrofitted it to a really old model). I got a replacement (under guarantee), changed the speaker to a square one and mounted it in a different place in the tender. The extra metal might mean the speaker needs more current to pull the cone in, but I don't know enough about speakers to know if this can happen.

[Leighton Cook]

2 front & 2 rear because I like the affect on the night runs.

Sorry no photos as yet.

 

[Leighton Cook]

No the speaker did not short out against the metal chassis etc, as allmy connections are liqid insulated if thry can not be insulated wit heat shrink.

Thanks for the comments though.

[walkingthedog]

2 front & 2 rear because I like the affect on the night runs.

Sorry no photos as yet.

 

Thanks. I only asked because it is fairly unusual to fit front lights to a steam loco as the lamps are moved depending on the type of train. 

 

They only have one on the rear and only if not pulling anything. Enjoy your trains. 

[Chrissaf]

It has been known for some Hornby DCC Ready locos to have their 8 pin NEM652 sockets cross-wired at the factory such that one of the motor wires gets crossed with a wheel pick up wire. This has no effect when a DCC blanking plate (plug) is fitted. But as soon as a decoder is fitted, the track voltage is connected (due to the cross wiring) onto the motor output of the decoder. When that happens the decoder is instantly fried.

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Use your meter to prove the wiring on the 8 pin connector before fitting any more decoders.

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Scroll halfway down this page for a diagram showing the NEM652 socket pin out wiring.

https://www.brian-lambert.co.uk/DCC_Page_1.html#Bookmark8

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Could I humbly suggest that you read my 'How to get the best out of this forum' post regarding your continual and unnecessary use of the quote button.

https://www.hornby.com/uk-en/forum/tips-on-using-the-forum/

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EDIT: Rob (RAF96) has highlighted something below that I hadn't spotted. The X in the R2784X denotes model is 'DCC Fitted' yet you have stated 'DCC Ready'. It can't be both, the two terms are contradictory. So which is it, Ready or Fitted. If it was 'Fitted', then it is unlikely to be a cross wired 8 pin connector issue.

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[96RAF]

The fact that more than one decoder blew definitely points to a dodgy installation.

 

After fitting a decoder it should be checked out on a programming track with limited current hence any bad wiring will create an error when reading the decoder and not a puff of smoke.

[ColinB]

Yes a know about the crossed wires issue, I blew up a very expensive sound module on a schools loco. I do exactly what you suggest now and check all the pins with a multimeter. Are you really sure using the programming output doesn't still fry the module. It seems to take very little current to kill these modules.

[96RAF]

The other thing of note is the R . . . . X suffix denotes this Mallard was DCC fitted at the factory therefore the wiring should have been pre-proven as it were. I have never heard of a tender drive loco being DCC fitted.

 

The whole point of the NMRA prog output lo-current ruling is to protect a decoder against dodgy wiring, as not only is there a current limit but also an elapsed time limit.

[Leighton Cook]

Thanks for all the contributors help especially how to reply correctly

 - The Hornby Millard tender I have is listed on Service Sheet HSS No. 344

- The motor is in the Locomotive and not the tender and DCC fitted from factory R2784X model

- Replaced DCC factory fitted decoder with new Hornby TTS decoder

- The TTS speaker fits neatly into the tender with extended speaker wires fully insulated at speaker & wire joints

- The lights I used were DCC Concepts Lanterns of the era

- What would happen if the exposed BLUE & GREEN wire ends touched during testing of the speaker? 

- I had these wires free from the lights when I tested the speaker. Silly boy I was.

- Maybe this caused the short

- I had been working for many hours on this reto fit so maybe tiredness and not being alert was the problem

- Thanks once again for all your for foroum advice from the members.

[Chrissaf]

The green function wire is a switched negative. So it would only short with the blue positive power wire if you had switched the green wire on (negative). Not sure, but I believe on TTS decoders that would be sending an F25 command.

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Similarly, the white and yellow wires would only be on after sending a F0 command.

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The blue wire however is positive permanently, so that could blow something if that touched the wrong place on the decoder or touched something that was carrying track DCC voltage like the wheels for example.

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[2e0dtoeric]

Replaced DCC factory fitted decoder with new Hornby TTS decoder

Why?

If the decoder was a loksound or similar, and you replaced it with a TTS, that's like putting a mini engine in a Ferrari!

[96RAF]

@Eric

The factory fit decoder would be a basic R8249 possibly even an old stock R8215.

A factory fit sound (ESU) model would be suffixed XS.

[2e0dtoeric]

Yes,  of course. Silly me! Where's my white stick?  😳

[Leighton Cook]

Thanks Chrissaf for your comments about the blue wire being positive permanently charged

- I guess that was the problem with the shorting against another exterior power souce.

- I know that the TTS decoders are very amp sensitive and a unprotected surage in exterior amps comming into      contact with the TTS decoder would fry it.

- I am impressed with  Chrissaf & RAF96`s knowledge and commitment to the forum - great job.

Thanks for all the advice from the Hornby forum team members.

[Fishmanoz]

Yes,  of course. Silly me! Where's my white stick?  😳

 

Eric, it will be at the flying field where you put it down to pick up all the bits at the crash site. 

[Leighton Cook]

Surprise - Surprise!!

Burn out ot TTS decoder solved after much mulimeter testing.

The "dummy" ringfield motor asembly in the tender of the Hornby Mallard R2784X

The speaker, 8 ohm 1 amp TTS speaker, fully insulated & fitted against the dummy ringfield motor burnt out due to the magnet amp flow being created by the ringfield cover plate circular contacts with no motor fitted.

The circular contacts still located in the shell circular shape of the magnet, a ring, creates the magnetic field to cause a much large amp flow ' pulled to the speaker"  than 1 amp via ambient flow of the current from the contacts being transfered to the speaker, even though it was fully insulated.

[Leighton Cook]

Why is a dummy ringfield motor shell fitted into the tender of the Honby Mallard R2784X?

- For more power pick ups to assist the locomotive?

 

[Ruffnut Thorston]

Not exactly...

 

But the tender pickups do help with continuity of power...

 

The model was originally made as a tender drive loco.

 

While the loco chassis has been retooled to have the can type motor driving the loco driving wheels, the tender uses basically the same chassis as the tender drive loco.

 

This clipped onto the Ringfield motor, so the basic casting of the motor shell has been used, but with different wheels and pickups.

 

The weight of the casting means that there is no need for a separate tender weight block.

 

So, a significant cost reduction, as  not so much new tooling required.

 

The other plus point is that, usually, the old tender drive loco and tender bodies will fit the new loco drive chassis.

 

This is good if you have a modified and detailed older tender drive loco and wish to upgrade to loco drive and DCC....or even to just have a different livery....

[96RAF]

Surely the dummy ringfield housing would not have any magnets, nor rotating parts apart from the wheels/axles, so how can it generate magnetic flux that could damage a speaker/decoder.

 

I still go with the dodgy wiring/short circuit theory as the dummy housing may be live.

[Bulleidboy]

 

If the decoder was a loksound or similar, and you replaced it with a TTS, that's like putting a mini engine in a Ferrari!

 

A one litre Ferrari - God forbid!

[96RAF]

 

If the decoder was a loksound or similar, and you replaced it with a TTS, that's like putting a mini engine in a Ferrari!

A one litre Ferrari - God forbid!

 

X fit locos had a Fiesta engine.  XS locos had a Ferrari.

TTS is a Fiesta with a boom box in the boot.

[ColinB]

My Railroad Mallard's tender has all the parts of a ringfield motor minus the armature. I just assumed Hornby was using up it's "left over" stock, or it was easier to supply. It has a really nice pickup for the other wheels in the tender, it is a shame Hornby don't sell them as a retro fit for the real ringfield motors, I definely would buy them. I suppose I never had any issues with sound as I mounted all of it in the loco and bought a small sugar cube speaker instead of the Hornby one. I don't know if is true, but I was told the sugar cube speaker is better than the Hornby one, but it is academic in my case as it didn't fit. I bought the loco second hand, the previous owner had detailed it and added non working front lights, so when I added the sound I added real lights and a smokebox led. Yes if you let the blue wire on the dcc touch anything it tends to blow up the module, I did a lenz one that way, I had even made sure it was well out the way, but as I put the loco body on, the whole lot moved and the module was no more. Now I insulate everything, As the blue wire goes to the module regulated supply, shorting it or connecting it to rail voltage is bound to blow it up.