ColinB

Having had so many issues with DCC decoders and damaging them when I put them into other locos to test them, I splashed out on a tester. It is wonderful, I had a LaisDcc decoder that I was using as a function decoder, when it stopped working. Put it on the tester in programming mode and it did exactly what I wanted, the one I have ( LaisDCC, no association with the Company) flashes a Led to tell you something is happening, and it is easy. Best thing I spent my money on.

I converted my Mainline locos and found that the DCC current was an issue. I used a 6 pin connector as this was the smallest. Wired in the 6 pin socket and initially used DCC Supplies 6 pin decoders. These failed in one way or another. Replaced them with Bachmann 6 pin right angled ones and it was perfect. I checked with DCC Supplies and they suggested it was over current that damaged their devices, so perhaps with the Hornby you are near the current limit. I am pretty sure it is the motor statup current that is the issue.

When I do it, I put in an 8 pin socket which allows me to use any 8 pin decoder, it also allows me to check it on DC once I have finished. I buy the proper Hornby 8 pin PCB, but you could make your own out of veroboard and two lines of 4 pin socket Also with the Lima bodies, it is quite easy to add lights as they do seem to have any cab detail..

Stall current is totally different to a short circuit and they can definitely cope with that (the motor has some resistance). In the specification is also says that they are short circuit protected, which I think they are. I suspect that this is only for a short time as they tend to heat up, so probably for about 30 seconds you are ok. I checked with another manufacturer and they said roughly the same, they don't have "fold back" current limiting (the comment was there is only a certain amount you can achive on electronics this small and I assume cost). As for the capacitor going short circuit, I have worked in electronics for about 30+ years and I have nver known it happen, but then I always used decent capacitors with a voltage rating way in excessive of the expected running voltage. I never used disc capacitors, as I remember reading once, that they were not reliable. Unfortunately, the one I removed was a ceramic disc.

Well, if you read my posts, on my 6 month old class 66 the suppression capacitor failed short circuit and took the TTS decoder with it. Thinking it was the TTS decoder gone wrong, I managed to damage another TTS decoder before I tracked it to the capacitor. On the Hornby class 66 it is hidden on the side of the motor within the bogie, so I could not even see it. Neadless to say, I now remove them.

I have just converted a couple of my Lima locos. If you don't mind wiring then it is not too difficult. The only issue is "pickups", Lima locos don't pick up from all wheels, but with traction tyres is there much use using a pickup on these wheels. In the case of their diesels there is lots of room to put in a huge bank of "keep alive", so it helps out a lot. Use a decent dcc decoder with provision for "keep alive" and they are ok. I have a class 66, I converted and added lights, it is a bit noisy but sounds a bit like a real one one under load. Adding new chassis and bogies gets expensive, by which time you might as well buy a Hornby "Railroad" version, unless you like doing that.

Sorry, I raised this one first, then noticed the other one in lowercase. Anyway, I bought new TTS decoder, tested loco with cheap dcc decoder that I could afford to lose (old Bachmann that is awful), and yes it works perfectly. I sent the broken one back for repair. I will fit it when it returns into my new class 59, which I have removed the capacitor from.

I had this fault when I fitted a DCC decoder to my ringfield based class 86, although it worked perfectly on DC. In the end I found that the ringfield was a bit stiff, once I had freed it off it worked perfectly. It seemed when running in DC there was more power to drive the motor. I was also advised to add "keep alive" as with my ringfield motor the loco doesn't have pickups on all wheels. I used a high current Zimo module as I was worried about the current. As it was a class 86 there was loads of room to add capacitors so that is what I did, it runs perfectly now. Perhaps you need to run the new brushes in on DC.

I think the big issue in this case was the cap failing. I naturally assumed I had a duff TTS module as generally locos are usually OK if they are not abused and it was only 6 months old and only been used a couple of times. I doubt it will ever happen again especially as I will be removing all the capacitors in future. In this case to get to that capacitor I had to virtually dismantle the whole of the front bogie, which I don't usually want to do on a new model. Once I figured it was the loco, it was easy to find it on DC, joke of it is before I put the decoder in I normally check for shorts between pins on the DCC connector and resistance across the motor, but as it was ok when I fitted it, I never bothered testing it again.

I can only comment on the Tornedo, if you look under the chimney to the front of the loco there is a plastic tube. The decoder should just about fit here. In the case of TTS you will need to get a small sugar cube speaker and bin the Hornby one, as it won't fit. Alternatively you could do is buy a 4 pin lead and put it all in the tender, but you will need to do some electrical work to rework the pickups and motor wires to the tender.. If you really get stuck, Zimo do a really small decoder that will fit. I found that other than the ones that fit in the tender, it is a real pain trying to fit a decoder inside a Hornby Loco, unless it is an A4 (there is quite a lot of room in these). If it a really small loco and Hornby do it with decoder fitted option, then that is what I buy, it saves the agro.

I think I might have figured it, it probably is short circuited protected, but only for a certain time, then probably it overheats. It doesn't mention a time, which probably explains why the sound worked on the second one for about 10 seconds before it died.

It is weird, now I have cleared the fault I put the original decoder back in and it does exactly what the second one does, goes backward at top speed, so the shorted cap did exactly the same damage. I got a returns number from Hornby so I will let them sort it out. I am intriged from the data it should be ok with a motor short and I am 100% sure it didn't touch any of the track inputs, as you say, been there killed modules so I am always very careful.I even checked all the lights had resistors on them, in case that caused an issue.

The first one is definitely dead, and it gets very hot, the second one goes backward at full speed with no control and no sound, so that is damaged. So if it is protected why did it blow, and that definitely was the only fault with the loco. It wasn't a track short it was a motor short. I will try the reset, but I don't hold much hope.

Great thanks Chrissaf, I have used them but I didn't realise that exactly what they were, I knew they reacted fast enough to protect electronics. There are a list of current ranges so I was going to pick one to suit the application. As for quality decoders having short circuit protection, I am not so sure about that. On all the decoders I have used it is never mentioned, the only exception was an old Backmann where it did state all outputs are short circuit protected. Perhaps someone can enlighten me as to which ones have it, I have been looking for ones with it for ages.

I recently had an instance where a motor suppression capacitor on my Hornby class 66 went short circuit. I know for DCC operation I should have removed it, but I didn't know it was there, it was burried next to the motor on the bogie. It subsequently blew up two TTS decoders, first one while it was running and then its replacement at which point I then started checking the loco. The TTS decoders have no short circuit protection, so if your motor goes short circuit, they instantly blow up. When I worked in electronics, I used to use resetable fuses to protect exactly this event, I wondered if anyone has any knowledge of whether they would work in protecting the TTS decoder from a motor short. In my case I am returning the two TTS decoders to Hornby under their replacement plan, as someone kindly pointed out to me, but I would rather protect against it happening again.

I eventually found the issue only after I had tried and damaged another TTS decoder. Amazingly it was the 9 month old loco that caused it. The capacitor across the motor had gone short circuit, I only noticed as I reverted it to DC and found the controller was being short circuited. The annoying part about all this is I normally remove the capacitors as recommended for DCC operation, but it was buried right next to the motor on the bogie so I never noticed it. TTS decoders are protected for stall currents but obviously not short circuits across the motor. When I first add a DCC decoder I normally check the resistance across the motor, but as it had been working I never thought to check it. Do you know in all my years of electronics I have never known a ceramic capacitor to go short circuit.

Actually I wasn't ranting, each of the decoders that have failed I have returned and yes they eventually get replaced (the last one about 4 weeks, I am still waiting for the one from Rails, but I am sure it will come). The one that failed yesterday, I immediately contacted Hornby for return. I was trying to work out if anyone else was having issues. From my experience and I worked in the stuff for a great number of years electronics is very reliable, so it seems unusual that so far I have had three bad units. Electronics normally fails because of excessive current, over voltage or excessive heat. They were fitted correctly, the only issue that does concern me, is cooling, where these are mounted there is not a free flow of air. If I had shorted something out, I would have instantly admitted to it, in fact in this case that was the first thing I did, check for stray wires. As for the 30 different variants out there, I assume that is the the same hardware all they are doing is replacing the memory map, for individual locos, that is how most people do it. There is still the possibility of a bad batch of components, and they don't make enough to really notice. I was actually asking for advice, so please don't assume I was ranting. I didn't realise they replaced modules if you blew them up.

Yes, I did a lot of work on this sort of thing before I retired. The USB to RS232 leads come in two sorts, some do true RS232 which uses weird votages or there is one that does basic logic levels to interface directly with 5 volt logic, so I assume it is the second type that they use with a bit of extra logic and a different connector. The reason I remember it so well was a Supplier supplied us with the wrong ones and it took a while to work out why the leads didn't work. The Fleishmann Twin Control system I use, uses a similar setup as I had to buy one so that I could upgrade the software to the latest level. I imagine if you look hard enough you can probably find a commercially available lead that will do the job, from what I read on the web this is an "Industry Standard" interface.

Mind you after my experience with my relatively new Hornby class 66 loco running a TTS module, that just failed, I am going off TTS completely. It is not the first failure either, I had had two where the sound didn't work from new ( fortunately replaced under warranty) and now I worry about the long term reliability of the other TTS modules I have fitted.

According to the data the Select supports XpressNet Protocol which looks vaguely like RS232, so I assume the lead is probably a USB to RS232 interface, but that is probably a guess. Most of them use an FTDI chip which converts USB to RS232, so this is probably one of the ICs you mention. Perhaps the other ICs are to get the right voltage levels or current loop.

I assume Railmaster is a PC front end to the Elite or Select units and communicates with these devices over the USB link, using the hardware in these devices to generate DCC decoder commands. So probably the first thing to do is check that the loco works backwards and forwards without the Railmaster software and just the Elite or Select units on their own. That at least tells you whether or not the basic DCC hardware is working properly. So if your loco goes backwards and forwards on the basic unit, then the error must be in the Railmaster software. It may be that the Railmaster software is issueing the commands to the DCC unit too fast, for that particular decoder so it loses them. I must load up my copy of Railmaster sometime to see what it does (it came as part of the Elite package, I bought off EBay). I suppose Hornby do not issue a specification containing the USB commands over the link.

I eventually found them in a service sheet, but I had to buy the con rods as well. The funny thing was Hornby were the only people to have them. When I looked again at the packs of ten, it said "waiting for supplies" which effectively means with Hornby, never. I am surprised Hornby don't do them as spare parts on their own as they do tend to undo and get lost on the layout. Surprisingly I had to order some parts off Bachmann for a couple of models (pantograph and DMU drive wheels) and they did all of them and were really helpful and I got a response within 24 hours, with Hornby it is usually at least a couple of days, usually to tell me they don't stock it anymore.

That is funny, I have just put a post on the same subject. Mine was perfectly OK, then just stopped, opened up the class 66 and the module was very warm, not hot. When I powered off then on, the module sort of made a bit of a noise then nothing happened. I am waiting for Hornby to come back on this. I like the TTS decoders as they are cheap (no much more than a decent decoder), but from my experience their reliabilty is a bit suspect. I wonder who makes them for them? I have had ones that suddenly lose their sound, then recover, one that went quiet then recovered, it does not give you a feeling of confidence in their product. I wonder if they under spec their components and if they get a bit hot they just fail.

Running my Hornby Class 66 round the layout and it was running perfectly OK, it did about 2 loops then it suddenly stopped. I thought just a dirty piece of track, but no the TTS unit had failed. When I opened it up, the TTS decoder was a bit warm but no burning smell. Powered everything down and then started again, TSS decoder make a copule of gurgled noises then stopped. I bought the unit in April, I ran it a couple of times when I bought it, but why now. I raised a repair request with Hornby, anyone else had issues. This is the third one that has failed, the other two were dead from new. If it was something I was doing wrong like shorting rail voltage to it, then I could accept it, but in all cases I did nothing wrong.

Yes, checked all that. My one has a separate earth lead so remove that and see if it still works, which is what I did. You can also do it if you have added extra pickups to the loco on the other bogie, if you turn them round, and just connect them to the motor does it still work? Did the same test on my old class 90, and it shorted the controller out, which I found out was due to the self tapper that screws into the chassis. Thank you for the help though.