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Hornby decoder overheated?


125_driver
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Hi, have a Hornby ttsclass 47 sound decoder which suddenly stopped working. Loco ground to a halt and on investigation I found the decoder scorching hot. On removing it and putting a blanking chip in loco was fine. 

So my question is, is there anything I can do , ie to repair it or anyone who repairs them, as they are 80 odd quid each??? Any suggestions? Thanks 

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You omitted to mention whether the Hornby TTS 47 decoder was installed in a Hornby 47 .... or another make whose known current draw (from simple measurement) is greater than the 500mA rating of the decoder.

If it occured in a well maintained Hornby 47, then its worth contacting Hornby.

If it occurred in a Heljan or similar 47 - then Caveat Emptor ... its not Hornby's problem if installed into an inappropriate loco ....  you may even have inadvertantly worked around the inbuilt protection in which it will switch itself off.  [ Changing bulbs to LEDs will helo reduce other current loading too ]

A Multimeter is much cheaper than a Sound Decoder.  But if you were also paying 80GBP for a TTS decoder - then I also recommend you buy them elswhere (assuming you are in the UK/EU) ... as that appears to be about double the going price.

 

TO PREVENT such a problem occuring with a replacement decoder of similar rating ...  V=IR shows that  with '12V' to the motor (about 14V on track), the motor resistance needs to be no-less than 24 ohms  ( 12= 0.5 x 24 ) ... and a quick test with a meter will identify if that is the case. NOTE that as the motor turns, 2 windings get switched into circuit together, in parallel - and this is the lowest resistance that will or could occur.   I have then added a 10ohm  5w resistor IN SERIES with the motor to ensure that the 500mA cannot be exceeded ... it will reduce the available top speed and power slightly ... but much less than going up in smoke 8-) .... but do ensure that both the decoder and resistor are able to dissipate their heat as easily as possible .... or they will still overheat.

 

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1 hour ago, Phil S said:

You omitted to mention whether the Hornby TTS 47 decoder was installed in a Hornby 47 .... or another make whose known current draw (from simple measurement) is greater than the 500mA rating of the decoder.

If it occured in a well maintained Hornby 47, then its worth contacting Hornby.

If it occurred in a Heljan or similar 47 - then Caveat Emptor ... its not Hornby's problem if installed into an inappropriate loco ....  you may even have inadvertantly worked around the inbuilt protection in which it will switch itself off.  [ Changing bulbs to LEDs will helo reduce other current loading too ]

A Multimeter is much cheaper than a Sound Decoder.  But if you were also paying 80GBP for a TTS decoder - then I also recommend you buy them elswhere (assuming you are in the UK/EU) ... as that appears to be about double the going price.

 

TO PREVENT such a problem occuring with a replacement decoder of similar rating ...  V=IR shows that  with '12V' to the motor (about 14V on track), the motor resistance needs to be no-less than 24 ohms  ( 12= 0.5 x 24 ) ... and a quick test with a meter will identify if that is the case. NOTE that as the motor turns, 2 windings get switched into circuit together, in parallel - and this is the lowest resistance that will or could occur.   I have then added a 10ohm  5w resistor IN SERIES with the motor to ensure that the 500mA cannot be exceeded ... it will reduce the available top speed and power slightly ... but much less than going up in smoke 8-) .... but do ensure that both the decoder and resistor are able to dissipate their heat as easily as possible .... or they will still overheat.

 

It is fitted to a Hornby class 47 yes , I haven't tampered etc. 

My issue with limiting the current as you suggest is the Hornby 47 is already on the slow side for my high speed layout and the idea that they would run even slower isn't really appealing. 

On eBay I have paid 75 and 80 respectively for class 47 tts decoders, they seem unavailable elsewhere and no longer manufactured. If you know somewhere selling them for 40 quid I'd be very interested, thanks. 

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The 10ohm resistor is to go in series with a Heljan 47 or many other Heljan UK diesel locos.

What period of manufacture is your 47 ?  

There are several 47's with TTS fitted on sale on Ebay at the moment ... but yes only at 85 for a 47 .....personally I would exercise patience ... it too me 2 years to get round to fitting all my TTS decoders ...having sent 12 back to Hornby for reprogramming in the meantime due to the facing which way problem.

Have you checked over your 47 with a meter to try and identify the cause ?

I have found the speaker wiring at the decoder end to be a point of risk .. and failure .... large amount of sleeving melted in assembly ... risk of contact with body replaced.

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1 hour ago, RAF96 said:

If you paid £80 then you were robbed, TTS decoders generally retail at less than half that.

How old is it as Hornby warranty on TTS is 1-year no quibble even for user error.

Interesting, unfortunately i wouldn't have the receipt but I bought it in a class 47 a couple of months ago, new. Would Hornby need proof of when purchased?

Also, a few people are now saying I've been robbed when buying decoders on eBay at 80, but where else are the Hornby 47 ones available for less? I have only recently returned to the hobby so may have missed the boat when they were in plentiful supply, as to the best of my knowledge now they are like hens teeth!!

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You potentially have a claim from the seller if it was advertised as brand-new. Furthermore, I assume you paid by PayPal who have a 6-month limit for claims if the item is faulty. Seems you are well within that limit so I'd pursue a claim for a refund via that path. 

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On 16/10/2019 at 05:25, 125_driver said:

My issue with limiting the current as you suggest is the Hornby 47 is already on the slow side for my high speed layout and the idea that they would run even slower isn't really appealing. 

 

I just ran a train around my layout at a scale speed of 60mph & it looked ridiculous as it looked like a TGV ! I have set most of my locos to do a maximum of 40MPH & that tends still to look slightly faster than it should. One layout in a an exhibition in South Australia had the Flying Scotsman really motoring & when a speedo was placed over it, it recorded well over 100 mph and in the opinion of many people ( including many modellers) who watched it compared it to the TGV & the like - too fast !

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1 hour ago, Sol said:

 

I just ran a train around my layout at a scale speed of 60mph & it looked ridiculous as it looked like a TGV ! I have set most of my locos to do a maximum of 40MPH & that tends still to look slightly faster than it should. One layout in a an exhibition in South Australia had the Flying Scotsman really motoring & when a speedo was placed over it, it recorded well over 100 mph and in the opinion of many people ( including many modellers) who watched it compared it to the TGV & the like - too fast !

Well the beauty of this hobby is each to their own. Just as i enjoy driving a real train at 125mph way more than pootling along through Cornwall, I like to run my models at similar "break neck speed". I don't intend to exhibit my layout, just a nice escape in the attic when I get a spare moment. 

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On ‎15‎/‎10‎/‎2019 at 17:14, 125_driver said:

Hi, have a Hornby ttsclass 47 sound decoder which suddenly stopped working. Loco ground to a halt and on investigation I found the decoder scorching hot...

The 500mA output is marginal for motor and sound. A somewhat more current hungry than average mechanism and/or speaker, and pop! You mention later that the loco was slower than you liked as it was: that may have been a slightly draggy mechanism, and that would cause higher current draw on the motor.

 

Measurement of current draw using a test meter would be a good plan ahead of decoder installation. Models can vary very significantly in this respect from example to example. One collection of 3 mechanisms of the same design tested running at 12V DC produced 160, 220, 350mA. That last one would be a 500mA output sound decoder eater for sure. (It was a noticeably slower and slightly noisier runner, problem a couple of gears not freely rotating in one bogie gear train.)

 

I'd also suggest reducing the sound volume to reduce current draw on the decoders.

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16 hours ago, RAF96 said:

If you paid £80 then you were robbed, TTS decoders generally retail at less than half that.

How old is it as Hornby warranty on TTS is 1-year no quibble even for user error.

It was mentioned earlier that TTS decoders are not currently available for a class 47, so supplies of new old stock will be low.

If demand outweighs supply, this will drive prices up.

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The TTS decoders I have tried just cut out if the load was over the 500ma and didn’t get hot so I think that your chip was probably faulty and I would be inclined to get in touch with Hornby for a replacement, they are quite helpful as there have been problems with the TTS chips.

 

 Regards mike 

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