Pendragon Sailing Posted May 3 Share Posted May 3 Here’s a strange one. I’m trying to install an 8 Pin decoder into my new Hornby J15 (R.3232). Loco works fine on DC and DCC (with a non-sound DCC Concepts Zen installed). Also the HM7000 works fine (sound and motion) on my decoder tester. BUT when installed in the J15, I’m getting sound but no motion……all very odd. Both the decoder and loco are fine separately, but when put together, only sound. Anyone else encountered this strange situation? Link to comment Share on other sites More sharing options...
Pendragon Sailing Posted May 3 Author Share Posted May 3 (edited) The plot thickens on this issue. The loco works as expected under DC control (with perfect motion control, both forwards and backwards), BUT under DCC control (both HM7K Sound and DCC Concepts Zen non-sound), while the motor runs forwards with no issues, it won’t run backwards without the motor labouring, stuttering and stopping frequently. I’m ignoring sound at this stage. I’ve tested the continuity of the wiring from the decoder PCB to the pickups and to the motor (all fine), and I’ve removed the loco drive-shaft (so there’s no load on the motor) and again all good under DC control, but regardless of the DCC decoder I use (three different ones), the same result…….forward motion absolutely fine, but backward motion problematic. This has completely defeated me…..never seen this behaviour before! Anyone have any thoughts? Edited May 3 by Pendragon Sailing Link to comment Share on other sites More sharing options...
Brew Man Posted May 3 Share Posted May 3 Apart from it working fine under DC control, it sounds very much like the gears aren't meshing properly. Have you checked that just to be sure? Link to comment Share on other sites More sharing options...
ntpntpntp Posted May 3 Share Posted May 3 (edited) I know you've tested continuity etc., but to me it sounds like a possible fault/short/solder-bridge between pickup and motor wiring on one side perhaps? That wouldn't show on DC, but on DCC when the motor has to be totally isolated from the pickups...? Edited May 3 by ntpntpntp Link to comment Share on other sites More sharing options...
Pendragon Sailing Posted May 3 Author Share Posted May 3 Mystery solved. After much diagnosis, it turned out to be a failed component on the PCB that receives the 8 pin decoder. Not sure what they are, possibly a capacitor or resister (see photo - the four thingys in the corners). Anyway, after replacing this PCB with a replacement, all is well…….very strange, but there it is. thanks for the comments and suggestions Link to comment Share on other sites More sharing options...
96RAF Posted May 3 Share Posted May 3 Ls are inductors and Cs are capacitors. Link to comment Share on other sites More sharing options...
Pendragon Sailing Posted May 4 Author Share Posted May 4 Thanks Rob. Any thoughts on why one of these would cause the observed running problems on DCC but not on DC? Link to comment Share on other sites More sharing options...
Rog RJ Posted May 4 Share Posted May 4 34 minutes ago, Pendragon Sailing said: Thanks Rob. Any thoughts on why one of these would cause the observed running problems on DCC but not on DC? Because DCC changes polarity at somewhere between 7 - 10 thousand times per second and the capacitors and inductors (aka chokes) distort the DCC signal. 1 Link to comment Share on other sites More sharing options...
96RAF Posted May 4 Share Posted May 4 It has to be a duff cap as they are in parallel. An inductor is in series so if it broke the power path would be broken in either dc or dcc. I have no idea what the tiny wedge shaped device is near the pin with the red wire seemingly attached - marked P1? Link to comment Share on other sites More sharing options...
Brew Man Posted May 4 Share Posted May 4 I've had one of those sockets fail on a Prairie I have. An annoying fault to be sure. Link to comment Share on other sites More sharing options...
Pendragon Sailing Posted May 4 Author Share Posted May 4 I replaced it with a simple decoder socket….no electronic gadgetry, just the 8 pin sockets and their wire connectors. I wonder why Hornby chose to use this particular version? Link to comment Share on other sites More sharing options...
dBerriff Posted May 4 Share Posted May 4 To comply with suppression regulations? Link to comment Share on other sites More sharing options...
ColinB Posted May 4 Share Posted May 4 Interesting fault, I have had the separate capacitors that Hornby fit round the motor fail but I would never suspect one soldered on the PCB. You say it works on DC but not DCC, to me it sounds like they fitted the wrong one with a higher value which is filtering out the DCC motor signal. If had failed short circuit it wouldn't work on DC. It is meant to filter out high frequency spikes that interfere with old analogue TV signals. Link to comment Share on other sites More sharing options...
Pendragon Sailing Posted May 4 Author Share Posted May 4 Ah, thanks Colin……I’m certainly no electrician, and these various electrical components confuse me at times. I understand resistors and their purpose, but all these other bits and pieces that find their way onto circuit boards are mostly beyond my understanding. As a general rule, for DCC operation I cut off the orange circular capacitors that are present, but hadn’t realised they can be in a different form if incorporated into a PCB like this one. You live and learn, I suppose.🫤 It took me a whole afternoon to figure out it was the PCB playing up….the situation had me completely flummoxed. Particularly when it ran perfectly on DC in both directions, and on DCC in one direction only. Anyway, problem now solved, and the J15 is up and running perfectly. Thanks everyone for their comments and suggestions. Link to comment Share on other sites More sharing options...
Pendragon Sailing Posted May 4 Author Share Posted May 4 (edited) 2 hours ago, 96RAF said: It has to be a duff cap as they are in parallel. An inductor is in series so if it broke the power path would be broken in either dc or dcc. I have no idea what the tiny wedge shaped device is near the pin with the red wire seemingly attached - marked P1? Rob, I’ve had a closer look at the failed PCB and the device marked P1 has the letters RO printed in it, if that helps identify it??? (a resistor, perhaps?) Edited May 4 by Pendragon Sailing Link to comment Share on other sites More sharing options...
dBerriff Posted May 4 Share Posted May 4 (edited) Who would have guessed that this would be a point of failure? You have every right to be flummoxed. Edited May 4 by dBerriff 1 Link to comment Share on other sites More sharing options...
ntpntpntp Posted May 4 Share Posted May 4 (edited) 38 minutes ago, dBerriff said: Who would have guessed that this would be a point of failure? When servicing locos for friends I've come across things like solder blobs on factory decoder socket installs which caused similar symptoms (works on DC, fails on DCC) which is why I suggested a wiring/component fault as a possibility. Edited May 4 by ntpntpntp Link to comment Share on other sites More sharing options...
dBerriff Posted May 4 Share Posted May 4 I never stop learning. I would have hoped basic testing would have caught it - but perhaps they do not test these things. Link to comment Share on other sites More sharing options...
Alain-358806 Posted May 4 Share Posted May 4 5 hours ago, Pendragon Sailing said: Ah, thanks Colin……I’m certainly no electrician, and these various electrical components confuse me at times. I understand resistors and their purpose, but all these other bits and pieces that find their way onto circuit boards are mostly beyond my understanding. As a general rule, for DCC operation I cut off the orange circular capacitors that are present, but hadn’t realised they can be in a different form if incorporated into a PCB like this one. You live and learn, I suppose.🫤 It took me a whole afternoon to figure out it was the PCB playing up….the situation had me completely flummoxed. Particularly when it ran perfectly on DC in both directions, and on DCC in one direction only. Anyway, problem now solved, and the J15 is up and running perfectly. Thanks everyone for their comments and suggestions. Hi Pendragon Sailing, just to let you know I followed your explanations by cutting off the orange circular capacitors, on my Grimsby Town B17, which has been down for a year now, and Oh miracle, it's up and running. Just need to install a sound decoder now. Thank you 1 Link to comment Share on other sites More sharing options...
96RAF Posted May 4 Share Posted May 4 7 hours ago, Pendragon Sailing said: Rob, I’ve had a closer look at the failed PCB and the device marked P1 has the letters RO printed in it, if that helps identify it??? (a resistor, perhaps?) R0 is a zero ohm resistor (i.e. a link thru') and they are used where the circuit was designed for a resistor but in the end it was not required. I guess P stands for Placebo. Link to comment Share on other sites More sharing options...
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