ColinRE

Hi Chrissaf, A long time since my last note so thought I’d better update you on the final status. What I found in June was that removing the capacitor from each coach resolved the short circuit and increased the overall resistance of each coach from circa 110 ohms to 360 ohms (the same resistance as an intact coach). In this state, I found the coach lights worked OK, albeit flickering a little more that with a working capacitor. I then had a go at replacing the capacitors. I did this with 4 coaches and my soldering is fairly proficient, but what I found was that it didn’t act as a capacitor but rather reinstated the short circuit. I spent a long time trying to understand this without success. Recently I concluded that I would live with the flickering LEDs and removed the capacitors from all 13 faulty coaches. The only problem I then found was when I tried to operate more than 10 flickering coaches in that they seemed to increase the propensity for short circuits when locos traverse points. My final status is to run with the 3 ‘intact’ LED coaches, 9 flickering ones and 4 with disconnected circuits. Thanks again for your help Colin

Chris, My lunch hour again. Thanks for all your hard work with the diagram and particualrly the efforts in producing Notes 1 and 2; - much appreciated and hugely helpful when it comes to swapping out components. Colin

Re 2eOdtoeric's comments The red square wire is in fact a rubber band used to hold wires in place for photographs The back of the PCBs isn't the best picture and yes what you can see is just tails rather than a fine bridge. The joint isn't dry, electicity will flow through it OK. Colin

Chis & FB, Apogies for my poor AVO reading skills, I got the decimal place wrong on the meter and the yellow and violet stripes were enough to confirmed my error. Interesting thread from 2011. Makes me feel less alone, although up until I had the fatal short circuit I have had all 16 coaches sitting on the track without circuit breaker issues at start up - hundreds of times. Also gives me some confidence that most of my pullmans will conform to the same electrical design, although 4 iof the problematic ones are very much older and inherited. Agree given R1 & R2 at 470 ohms, the capacitors now look to be the most likely cause. I have got as far as ordering some from Radio Spares but experimenting with them will have to wait till I get back from hols in June. Many thanks for your help; will let you know how I get on then. Colin

Hi Chris & FB, Thanks for your thoughts. This is my lunch hour so a bit limited, but happen to have additional pictures I took yesterday on my work PC that clear up most, if not all your questions. R1 is definately 47 ohms from markings and I checked it with the meter The Capacitor looks to be 25V and 220 mico farads from the writing /media/tinymce_upload/d0d0dcdb4d47c368cb168dbddab25fe0.JPG /media/tinymce_upload/dd0ed4ce77a275dfb8d352f048f7de09.JPG /media/tinymce_upload/68a77e05b3c0d70c32248fe9eba490a0.JPG The pictures of the undersides of the PCBs are not the best, but perhaps sufficient to indicate the circuit design. I reiterate there is no melted solder underneath connecting what shouldn't be connected in spite of the reflected light hinting at this. Working on the principle that the culprids are either the capcitor or the LEDs I will progress with your respective suggestions for both (capaciot first) and then FBs suggestions to separate the boards. I happen to have some spare (red) LEDs (good enough for a test) left over from putting the circuit breaker box together. Would I be right in assuming they are pretty standard and interchangeable? I know that one wire is longer than the other, BUT which way round do they go in the circuit board. From the photo the underside of the existing LED has been trimmed (so no clue there). I can of cause just try it and hope to be lucky first time, but would rather avoid 'fireworks'. Suspect the next steps towards repairing the lights may not happen now till mid June as going on hols Friday night for couple of weeks, but I will update this post as soon as I do make progress. On the plus side I put the spike filter in place across the BUS last night. Colin

Yesterday (Saturday) I uploaded a posting with photographs and measurements regarding the individual electrical components on the PCBs in a 'problematic' coach. Because of the photograph these havn't appeared yet as verification is necessary. The results were not quite what I expected and I feel I'm still missing something. The only two components I haven't specifically measured with a meter are the capacitor and the LEDs themselves. As a sense check and to provide additional information I decided to have a go at measuring the resistance of whole coaches by connecting up a single length of track to DC power, putting a coach on it, measuring both volts and amps and then calculating resistance from volts divided by amps. The results were very clear, consistant and showed a big difference between 'good' and 'problematic' coaches The 13 'problematic' coaches all have an overall resistance of 110 ohms plus or minus 10ohms The 3 'good' coaches have an overall resistance of 365 ohms plus or minus 2ohms I'll leave readers to combine the above information with that from yesterday's post (when it appears). I'm sort of concluding (based on rather weak electrical skills) that it may be down to the capacitors or LEDs themselves, although both seem to fullfil their basic functions at an 'observational' level. All suggestions on a route forward greatly appreciated. In the absence of better ideas, my next step would be to measure the individual components in a 'good' coach to see if anything is different. Colin

Responding to Chrissaf’s kind offer to have a look at the coach PCBs, I took one of the problematic coaches apart (surprisingly easy) and pulled out the 2 PCBs for a photography session (see below). At one end there is just an LED and a 47 ohm resistor. At the other end an additional capacitor and, as Chissaf pointed out, 4 diodes forming a bridge rectifier. Hoping I might see something obvious - like a fried component or some melted solder underneath, but it all looks pristine. I took the opportunity to test the components with a meter. The resistors are both fine with values correspond to the 47 ohm markings. The diodes all recoded 664 ohms in one director and infinity the other way; their marking aren’t fully visible (so cant confirm against design) but looks like N40 on the top line and M10 underneath. The capacitor showed it could charge up. I didn’t try to test the LEDs as I’m not sure how to this with meter, but I did connect up DC power to the coach wheels again and this shows they light up and that the capacitor does its job in smoothing flickers from inconsistent pickup So execpting confirmation of the diode design characteristics all the individual PCB components seem to be working? Or am I missing something obvious here? I also took the opportunity to check the internal red and black feed wire insulation, to make sure there is no continuity where there shouldn’t be….and there isn’t The coach still trips the EB1 on DCC power and, as I said previously, 5 or 6 problematic coaches together on a free standing length of track cause my old faithful DC transformer to buzz unhappily. In summary, I’m no longer sure I know what the root cause of the problem is but clearly there is a lack of resistance across the whole assemble. Grateful for any suggestions on a way forward. Point of detail and an aside from above, responding to Chrissaf’s question on Friday; the twisting on my BUS is about 3 per meter as I read Brian Lamberts guidance last year before building the layout. /media/tinymce_upload/f8a9804dff68abf2589e7bd035716d1e.JPG/media/tinymce_upload/061859c1f7d4deb7c02d2460d8bc0908.JPG

Many thanks to Chissaf and Fishmanoz, I feel confident you have clarified the problem and I will be putting the filter you suggest in place over the weekend. I did in fact consider this when I built the layout last year, but given my BUS is only about 7M long and well twisted I didn't think it to be necessary. Hindsight is a wonderful thing! Colin

Hoping someone may be able to throw some light on my experiences. I swapped over to DCC about 6 months ago. I have an NCE Power Pro controller with a 5 Amp supply protected with an NCE EB1 circuit breaker. My layout includes 6 circuits and I operate up to 6 trains at once. I have about 25 loco mainly fitted with Hatton’s decoders. My rolling stock includes 16 Hornby Pullman cars of varying ages, all with lighting (which is permanently on with DCC). This has all worked amazingly well for more than 6 months. A few weeks ago however, there was a short circuit and the EB1 cut the power as it is supposed to do. With lots of trains running and 40 points, short circuits are not uncommon. Usually they are momentary as a loco passed a point or a derailment occurs and the problems clear themselves. In this case it didn’t and the EB1 continued to operate switching the power on and off every few seconds. After lots of experimentation I narrowed the cause to 13 of the 16 illuminated coaches. Usually putting just 1 of these problematic coaches on the track and certainly 2 causes the circuit breaker to trip. I cleaned the pickup wheels on each coach and established that there were no short circuits across wheels on the same axle and that there was continuity between the wheels on the power pick-up side of each bogie. The power for the lighting is picked up from across both bogies (from diagonally opposite wheels) so you would expect to find continuity there – and I did. Inside the coaches the light to the window lamps is supplied via fibre optic leads from an LED at each end mounted on small circuit board which includes some resistors and at one end a capacitor – presumably to smooth any flickering. I tried to measure the resistance between the power pick up wheels using a multi-meter, hoping to compare the difference between the working and problematic coaches, but I was unable to achieve a reading - perhaps because of the capacitor? I conducted a bench test putting 6 of the problematic coaches into a free standing length of track and connected up my old faithful Tri-ang DC controller from my childhood. With a few volts flowing it buzzed unhappily indicating a heavy load/short circuit. A second test was to disconnect the red feed wire between the power pick up and the circuit boards inside the coach. Result no lights (obviously) but also no short circuit identifiable on either DC or DCC. 3 coaches with disconnected lighting run happily on DCC. My conclusion here, and I might be wrong, is that a power surge on DCC has damaged the circuit board in 13 of my 16 carriages – and some or all of the resistors are no longer effective. Has anyone else encountered anything like this? I assumed 6 months ago from everything I read that Hornby’s Pullman coaches could make the transition without any special precautions. Have I missed something? Should I worry about the 3 remaining coaches that work? Are replacement lighting circuit boards available for the failed coaches? Thanks in anticipation Colin