Merchant Navy TTS Sound decoder (R8115) problems

[Aussie Jon]

I purchased two Merchant Navy TTS Sound decoders (R8115) from Hattons a couple of months ago and installed them into two Hornby Merchant Navy locos (one DCC fitted and one which I had converted to DCC.) On initial startup they worked fine. Subsequently they didn't start up properly and I had to either re-register them or disconnect then reconnect them to restart. It was an entirely hit and miss affair. In addition there was some erratic behaviour when they were connected with one of them continually stopping and restarting and blowing the guard's whistle. I tested both locomotives with other decoders and they both work fine. I also tried the decoders with different locomotives with the same results. I also read all the instructions but I couldn't find anything to help so could only assume they were faulty.  I returned them to Hattons who replaced them with new ones. Guess what? The new ones are doing exactly the same thing. I have other TTS decoders which work perfectly well on my layout so I know it's not a problem with the track, locomotives or connections.  I don't know whether to return them yet again to Hattons or whether Hornby can solve the problem. It does seem like there is a fault with this batch of decoders. Any advice would be most welcome. Cheers!

[96RAF]

If it is a faulty batch then you will get the same result from Hattons until you have exhausted their stock.

 

Which controller are you using. Select, Elite or eLink with RM or some other make - if so what make and model and if possible the firmware revisionof your controller.

 

If a TTS spot sound function is set to and left on then it will oddly replay at random with some controllers due to the way they handle momentary and toggled functions. Why - I have absolutely no idea but I have had a few do this.

[Rog RJ]

One other possibility is that the locos themselves are causing the problem.

 

I'm not saying the locos are faulty as such, just that something about them isn't happy working with the decoders.  It may be that removing the motor suppression capacitors, if you haven't already done so, will cure the problem, for instance.

[sir john]

Hi Jon

I had the same problem I have 2 merchant navy's 1 rebuilt the other not the unrebuilt was factory fitted with a tts decoder and works fine 

The other I fitted myself it ran for about 20 minutes then the sound stopped removing from track cured the problem for 10 minutes then stopped again 

I returned the decoder to Hattons fitted the replacement same thing it's been back to hornby twice but is still the same so I only run it for 10 minutes at a time a complete mystery

Regards john 

[Aussie Jon]

Thanks for your advice gentlemen. I program my locomotives using a Hornby 'Select' controller on a service track but the main layout uses a Hornby 'Elite' unit. The units seem to be compatible and all programmed locomotives ( except the ones with the Merchant Navy decoders) easily interchange between the two. The fault is evident with both controllers. I won't return the decoders to Hattons as you're right in suggesting I'd only get another couple of faulty ones. I wonder if Hornby could shed any light on the problem themselves. Cheers Jon

[96RAF]

Jon

The Select snd Elite are compatible noting the previously mentioned address range limitations, which could be a pest for some users with  large fleets or who prefer to use long addressing.

 

You are obviously aware that you must never connect 2 controllers together except by way of a walkabout cable.

[96RAF]

According to Hornby there has only been one batch of MN TTS which included factory fit units and retro kits, so if it was a duff batch then they would all be duff and as mine works OK and there have been relatively few reported problems, I think we can rule a duff batch out.

 

Most likely cause is dodgy pickups (also according to Hornby), who recommend checking the decoder in a static test rig such as an ESU unit or a known good slave loco. It is possible that a short has damaged the decoder but for this to keep happening time after time points to a loco fault.

[sir john]

@RAF96

RAF

As I said in my previous post my MN went back to hornby twice first time they rewired the pcb made no difference next time they changed the decoder still made no difference will not run for long periods with sound on sound off will run for hours track is clean all other tts locos work fine complete mystery

John

[Rog RJ]

Have you thought of removing the motor suppression capacitors as I suggested earlier?

[sir john]

Roj 

I have checked there are none present so remains a mystery

John

[96RAF]

From that we can deduce the decoder is coping with motor loads but adding sound into the equation tips the scales. There must be a high resistance in the pickups which is drawing more current than you would expect. Unfortunately there is no easy way of checking actual current draw on track with a DCC loco without a fairly expensive bit of monitoring kit. Try a resistance check from each wheel to the decoder socket looking for an odd high value.

[sir john]

@RAF96

Thanks for the advice am at my holiday home at the moment will try when I get home in 8 days time then report back 

Regards john 

[Fishmanoz]

Rob, think about high resistance drawing current - the limit to high resistance is open circuit and draws no current at all.  Low resistances draw current (the limit here is short circuit and lots of current).

[96RAF]

Correct Fishy

Either way it looks like the sound load is taking the TTS decoder out of limits, but with the basic motor/loco load probably being a higher than normal level starting point.

[Aussie Jon]

Thanks again for your advice. I have installed one of the decoders into another loco and (touch wood) it seems to be working ok. Will keep perservering. Cheers Jon

[big_ian_2003]

I am having the same problem with my loco and wondered if anyone had come up with a solution. I bought a Merchant Navy (R3617) with a fitted MN TTS decoder (R8115) from Hattons. It would run for a while then suddenly stop dead, requiring a reset to get it going again. I returned it to Hattons who returned it to Hornby. They retuned it to me with a note saying the pcb on the loco had been resoldered and it should be ok. The problem persisted so I returned it to Hattons again and this time they sent me a replacement loco with replacement (fitted) TTS decoder. It seemed ok but after a while it displayed the same problem, namely stopping dead on my track. All other TTS fitted locos run well on my layout and my track is clean. Any help much appreciated.

[96RAF]

If you can check the motor stall current by fitting a blanking plug and measuring on DC. It could be the motor is running close to the decoder limit then when the sound is on it tips the self protection in and the loco stops.

 

The other suggestion to swap decoders twixt the duff loco and a good loco is also a simple proving exercise. See if the faults stays with the loco or follows the decoder.

[Fishmanoz]

Interesting, now we have 3 MNs with the same marginal current draw fault. I wonder how many more are like this and is it the locos are drawing too much current or the decoders delivering under the 500mA spec?

[96RAF]

I have an MN packed away somewhere loaded with TTS.

I can pull the decoder and do a stall test on DC but I wonder if anyone can suggest a way of checking the decoder cutout limit.

[ColinB]

I assume somebody has already done this, but it is an idea. Hornby made different versions of the Merchant Navy over the years, I know on the early ones (80's) they had a different motor, could this be the issue? I know it is a different supplier, but I added a smoke unit to a Zimo unit of a West Country and the loco kept stopping, took the smoke unit off, and the loco works perfectly. Before you say it, there was no smoke oil on the track. 

[96RAF]

The smoke unit was obviously tipping the decoder over its current limit.

[Fishmanoz]

Colin, it would be good not trying to set the hares running without first checking what the posters have said.  One MN is the current model DCC ready, 5-pole skew-wound motor, another is DCC fitted, (we don’t know the third).  They will both be designed to run with an 8249 or equivalent (includes TTS).  So old motor type high current draw appears not to be the issue from what we already know.  

 

The common factor is modern MNs, TTS fitted are exhibiting marginal current overload behaviour. Or more specifically, the common factor is MN TTS so possibly this specific decoder having below spec current capability.

 

I could of course be completely wrong but this is my conclusion from the info available. Older higher current motors does not appear to be a common factor.  The fact you can produce overload in another loco type with another decoder type and a smoke unit fitted is also not relevant here.  I agree with exploring alternative theories to reach the final resolution but the alternatives need to fit the facts available. Keep your mind open and thinking but also stick to what is known.  Healthy speculation is good too where facts might be unclear but, again, we have pretty clear info on 2 MNs here.

[ColinB]

Yes, that is what I figured, unfortunately it eventually stopped the module working. I took the unit off, sent the unit off for repair and it all works perfectly. The smoke unit was very messy, and it did worry me about the heat. Next time I will make a suitable buffer circuit and find a less expensive loco to fit it to. Funny though when I questioned whether the Zimo had the current drive, I was told it had. Trouble is trying to fit electronics in a very hostile enviroment, once you put it all together, is it virtually impossible to see what is touching what. Hornby's idea of putting in the tender seems a much more reliable option, but even then quite often, the fitting is very badly engineered.

 

[Fishmanoz]

Can we please stick to topic until the issue is resolved, and not use the white arrow in blue box to reply.

 

To recap, the problem is 3 MNs TTS fitted exhibiting marginal current overload or under-supply.  Two known to be modern so should be well within current spec, one unsure of age.

 

For the new ones, return to Hornby for further investigation would seem a good option.  Refer them to this thread for detail particularly 3 having same/similar problem.