Wolf27 Posted April 13, 2020 Share Posted April 13, 2020 (edited) Hi All I had a spectacular failure today of my part built Bachmann 25. It is/was fitted with an ESU? V3:5 sound chip. The loco was sat on the track and not running but the motor got so hot it melted the cradle it sits in and also the plastruct underframe. The chip is also fried. I discussed it with Mark (Miller) and he has never known anything like that. The motor is damaged, but I have a spare and the loco is salvageable but not the chip. Untitled by Shane Wilton, on Flickr Untitled by Shane Wilton, on Flickr The focal point for the damage seems to centre around the suppressor, which is soldered to the motor casing at one end and the brush holder at the other. Untitled by Shane Wilton, on Flickr Any suggestions as to how this could have happened? Cheers Shane Edited April 13, 2020 by Wolf27 spelling Link to post Share on other sites More sharing options...
NIK Posted April 13, 2020 Share Posted April 13, 2020 Hi, I have a guess of how (assuming you were within earshot of the loco all the time the DCC power was on and the loco never moved). The motor could have been fed with high frequency pulses from the decoder (the current going in one direction and then going in the other). Many DCC decoders put out high frequency pulses to the motor but only in one direction (current wise) for a loco going forward and the opposite direction for the loco going in reverse. These pulses can be above the frequency range of human hearing. DCC decoders don't normally produce any motor pulses at speed step 0. I see you didn't ask why, an answer to that may need to be more information provided. What does 'part built class 25' entail?. What is the white plastic shown and what temperature does the plastic melt at?. Who is Mark Miller?. Can you show very clear photos of the DCC decoder, the PCB on the top of the loco and any wiring you have added. Take care. Nick Link to post Share on other sites More sharing options...
Wolf27 Posted April 13, 2020 Author Share Posted April 13, 2020 I see you didn't ask why, an answer to that may need to be more information provided. I did at the very end of the topic What does 'part built class 25' entail?. Its a Hornby body on a modified Bachmann chassis - modified by cutting out the fictitious solebar and making a new cosmetic underframe, these are the white bits that have melted. What is the white plastic shown and what temperature does the plastic melt at?. see above Who is Mark Miller?. A friend who is a member here Can you show very clear photos of the DCC decoder, the PCB on the top of the loco and any wiring you have added. The PCB with chip removed Untitled by Shane Wilton, on Flickr both sides of the decoder Untitled by Shane Wilton, on Flickr Untitled by Shane Wilton, on Flickr Link to post Share on other sites More sharing options...
RMweb Premium Ray H Posted April 13, 2020 RMweb Premium Share Posted April 13, 2020 I can not see any obvious signs from your images of the decoder getting warm. What have you done to test it since the incident. Have you checked that the speaker is still working as I've had one go open circuit for no apparent reason. Link to post Share on other sites More sharing options...
Wolf27 Posted April 13, 2020 Author Share Posted April 13, 2020 I’ve tested the decoder in another 21pin chassis and it’s shorts straightaway. Not tested the speaker yet. Link to post Share on other sites More sharing options...
NIK Posted April 13, 2020 Share Posted April 13, 2020 Hi, Very clear photos of the top of the decoder and the loco PCB. Shame the bottom side of the decoder has sticky labels on them. Having looked at a few failed decoders in the past I was expecting to see obvious damage to the H bridge FETs (the transistors that drive the motor) but I can't see any. There is a sign of a strand of something between one of the PCB pads and one of the holes where the loco PCB DCC connector pins comes through. However it looks white like PCB labelling ink rather than shiny solder but that could be a trick of the light. So for now all I can offer is guesswork based on the following: I noticed a file next to the loco and it wasn't clogged up with white plastic. Some high end decoders deal with more than one Digital CC protocol as well as DC compatibility mode. Sticky labels are a place where detritus can collect including metal swarf. The diecast metal used in most chassis tends to catch the tool and then a strand of swarf peels off. As I said no obvious sign of damage to the two thirds of decoder components that can be seen. So my guess is a contact was been made between one of the DCC connections and another connection to/from the DCC decoder. My guess would be one of the connections from the pickups (from track), the other one of the speaker connections. Somehow this put the DCC decoder repeatedly into a strange mode (test mode?/ start up mode/motor check mode/connection cleaning mode or some sophisticated ACK mode using HF AC*). * I don't know if any sound fitted locos can be reprogrammed while the loco is still on the track. If so they might need an HF AC ACK in order for the loco not to crawl off the end of the programming track. Take care. Nick Link to post Share on other sites More sharing options...
34theletterbetweenB&D Posted April 13, 2020 Share Posted April 13, 2020 I feel that is nothing more complicated than the motor got DCC track power supplied to it. If track supply is reaching one or both the motor outputs of the decoder, that will generate enough heat as the motor stands conducting to produce the observed melting and will fry the decoder. Wiring fault(s) in short. Had the decoder installation been checked on programme track while in its present configuration? Link to post Share on other sites More sharing options...
NIK Posted April 13, 2020 Share Posted April 13, 2020 1 minute ago, 34theletterbetweenB&D said: I feel that is nothing more complicated than the motor got DCC track power supplied to it. If track supply is reaching one or both the motor outputs of the decoder, that will generate enough heat as the motor stands conducting to produce the observed melting and will fry the decoder. Wiring fault(s) in short. Had the decoder installation been checked on programme track while in its present configuration? Hi, Wouldn't Shane have heard the loco motor buzzing if it had a DCC track supply connected to the motor outputs?. Take care. Nick Link to post Share on other sites More sharing options...
34theletterbetweenB&D Posted April 13, 2020 Share Posted April 13, 2020 42 minutes ago, NIK said: ...Wouldn't Shane have heard the loco motor buzzing if it had a DCC track supply connected to the motor outputs?... You might think so, but I can immediately name several factors that might prevent this being heard: concentrating on another task, a little distance, other masking noises, gone to make a cup of coffee, significant mid range hearing loss. And maybe there wasn't much noise. My one experience with a friend of attempting to use the address 0 feature - at friend's request I should add - on his DC loco with a Mashima 1830 produced a large cloud of (very realistic) smoke as the motor windings swiftly overheated and burned out. My DCC system (rated 4.5A) didn't cut out either, the couple of moving trains on the layout all kept going. Nothing to be heard above the sound of moving trains, a very modest masking noise. The significant question for my money is whether the decoder installation had been checked on programme track with the loco wiring in that configuration at time of burn out. Link to post Share on other sites More sharing options...
charliepetty Posted April 17, 2020 Share Posted April 17, 2020 Is the speaker 100 Ohms, as it needsto be for a V3.5. Charlie Link to post Share on other sites More sharing options...
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