cga

Hello Nigel DC running has always been turned off in CV29 Loco with same decoder behaves exactly the same on a 1 meter test track used with main layout disconnected. All other locos behave normally on the main track and the test track. I have now tested the troublesome decoder in a Bachmann Jinty using an eighty-pin to six-pin adaptor. The problem is transferred with the decoder and is clearly an incompatibility between this decoder and this particular loco. The inductors have been removed and any effects attributable to them can be eliminated. I will in due course try another design of decoder. If you do try another decoder I would be interested to hear how you get on. The recently elevated temperatures, as suggested by Phil, were not the problem, I did check during the heatwave and everything remained exactly the same with all but this one loco operating normally. Mike

Hello All, A partial solution but another mystery. Setting the loco to 28 speed steps prevents the run-away. However, now it is no longer possible to set a maximum speed. Changing back to 128 speed steps restores the run-away in one direction, exactly as before, but does allow the maximum speed to be set. Can anybody explain this? Mike

Hello All, Now the temperature has dropped back a few degrees I have been able to get up into the loft again. The very jerky running seems to have been cured by adjusting the power leads to the motor. DC running is fine. The runaway remains. Occasionally the loco does seem to come to a stop as it ought, but if it is prodded, or moved back a few inches, it starts crawling again suggesting that it had stopped because it had found a portion of slightly dirty track, entered a curve or a gradient such that the current reaching the motor could not cope with this increased load. Have you noticed this Norm, or has your modification to the inductors fully solved the problem. I think that the cause of this running away must be a high-resistance short on the PCB as suggested by Bachmann, but I cannot find a short, and am puzzled by why it should operate only in one direction. If this is indeed a case of a faulty PCB, it raises an interesting warranty question. If a loco is bought DCC-ready in anticipation of adopting DCC at some time in the future, and that adoption and recognition of a problem does not occur until the warranty has expired, is that not rather unfair on the purchaser? The only way to circumvent this is to require that the loco to be tested at the point of sale with a chip installed so as to be assured that all is in order. As always comments and suggestions welcome. Mike

Thank you for the suggestion, but power supply is not the problem, as this problem occurs also on the test track and on the decoder tester. Mike

Hello All, Have removed the inductors one by one. Removal of the one across the motor had no effect. Removal of one input had no effect. Removal of the third as a last resort I regret to say the loco is worse. Very jerky running, sudden acceleration and then stops even on 001 speed setting. Not sure what to do now. Mike

Hello Nigel and Nick, Thank you both for the additional information on inductors and capacitors. Can either of you explain why the effect Norm and I have seen operates only in one direction. Are inductors 'directional' in a similar manner to diodes? From what I have read it doesn't seem as though they would be, but there is no doubt that the effect we see does apply only to one direction, and adjusting CV29 changes the effect to the other direction. Mike

Hello Norm and Nick. Nick, thank you for the clarification regarding inductors and capacitors. I was inclined to think they must be inductors (A-level physics was a long time ago) but nearly all the literature describes them as capacitors. Norm, thank you for the report of breaking the circuit across the brushes. I will try that on the half-cab in the next day or so and report back. Mike

Hello Norm and Nigel, Look forward to hearing how you get on. A link to some interesting comments about the Zimo MX622N, http://www.rmweb.co.uk/community/index.php?/topic/78457-farish-2mt-and-zimo-mx622n-stuttering/, including some by Nigel. Mike

Hello Norm, While I was posting my previous message on this thread I had an email from DCC Concepts with some interesting information as follows: "Most decoders these days will work with capacitors fitted, but there can sometimes be a situation when all the allowable tolerances within the electronic components combine to cause a problem. Although many components are fairly low manufacturing tolerances, capacitors can be up to +/- 20%, particularly for the small surface mount items". Their recommendation remains to remove the yellow capacitors. Mike

Hello Norm, At the moment I don't have another six-pin decoder to try in the half-cab so it is sitting on the naughty siding. The problem is also transferred to an ESU decoder tester so clearly the decoder is a significant part of the problem, and while I can't see capacitors on the tester presumably some or their equivalent must be there so that the tester complies with the relevant legislation. I haven't found anything useful relating to the back-emf CVs. Such accounts as I have found say these CVs can be adjusted to switch off the back-emf but don't say what value is required to do that. I think all my Bachmann locos have the three yellow capacitors on top of the motor, but DCC Concepts did say that sometimes one is hidden below the motor, and that is perhaps the case with the USA tank. DCC Concepts also said that as a last resort they have removed them with beneficial results. Unless we receive some new information it looks as though the only options remaining are isolating the capacitors or hard wiring a decoder that we know tolerates the capacitors. Mike

Hello Norm, Thanks for your input. Sorry to hear you are having problems but good to know I am not the only one. Since my post yesterday I have located an eight-pin to six-pin converter and transferred the troublesome six-pin ZEN decoder to a Bachmann Jinty. This transfers the problem, so clearly the decoder is part of the story. The Jinty runs perfectly with its normal ZEN ZN8D decoder. I have again contacted DCC concepts to see what if anything they can suggest. They found that my troublesome decoder (which I had returned) worked fine in a DJM/Hattons 14XX tank and a Hornby 08. I will investigate further the back EMF CVs and see what I can find out. Mike

Thank you all for your helpful suggestions. DCC Concepts have tested the decoder and find it performs to normal specifications. Gaugemaster have checked the controller and likewise find it operates to specification. Bachmann suggest a high resistance short on the PCB. I have checked for shorts across pins 1 and 2, and 3 and 4, and can find no evidence of a short. I have tried a decoder reset but no change. I have tried reducing the start voltage (CV2) as suggested and find the minimum that gives smooth running on the 001 speed step is SV = 13, but it is happier on 14. With this start voltage setting and Acceleration and Deceleration both set to 15, with DC compatibility turned off, the run away problem remains. With 001 speed setting and running forwards the loco stops in about one inch when speed reduced to zero. When running in reverse the loco trickles along slowly, sometimes stopping when it enters a curve or the foot of a gradient. With a speed setting of 050 and running forwards it is clear that the loco decelerates to a crawl in about 8 inches but then trickles along. With a speed setting of 126 it decelerates in about 2 feet and then trickles along. I am inclined to try hard-wiring a decoder but would welcome alternative suggestions. Mike

Thought I should let you know that I still have no response from DCC Concepts despite phoning them to ask what had happened to the email sent May 9th. Disappointing to put it mildly. Mike

Hello Tony, Thanks for your response. Other locos have Zen or Gaugemaster decoders, but this is the only 6 pin so at the moment I can't swap. I have used a programming track, and the settings are OK. I have reprogrammed repeatedly and, for example, can change acceleration, deceleration, top speed, etc easily, but the misbehaviour remains. I will recheck the pickups, but when tested this morning each wheel was picking up current OK. Also, I have tested the chip on an ESU chip tester and the peculiar behaviour occurs there so it must be the chip. Am waiting for a response from DCC Concepts. Thanks, Mike

Hello Nick. I did not use the stay alive. I did mean setting the throttle to zero Other locos have Zen or Gaugemaster decoders, but this is the only 6 pin so at the moment I can't swap. I have used a programming track, and the settings are OK. I have reprogrammed repeatedly and, for example, can change acceleration, deceleration, top speed, etc easily, but the misbehaviour remains. I will recheck the pickups, but when tested this morning each wheel was picking up current OK. Also, I have tested the chip on an ESU chip tester and the peculiar behaviour occurs there so it must be the chip. Am waiting for a response from DCC Concepts. Thanks, Mike

I have a Bachmann half-cab (41708) fitted with a Zen ZN68 6 pin DCC chip, operated by a Gaugemaster Prodigy Wireless. It runs perfectly in reverse on 001 speed setting. It runs perfectly forwards on 001 speed setting until I shut down power whereupon nothing happens and it just keeps rolling along. If I run at higher speed settings in reverse behaviour is fine and loco stops with appropriate deceleration when speed reduced to zero. At higher speed settings forwards the loco does slow down when speed zero is selected, but does not stop. It will continue for over 1 hour on the 40 foot long circuit quite happily. When running forwards I found by chance that pressing reverse will stop it (I was aiming for the emergency stop and hit the wrong button). Settings are SV =30; Acc = 15; Dec = 15; TV = 100; CV 6 = 35; CV 29 = 34. Switching off the optional DC operation in CV29 has no effect. Setting CV 29 to 35 as expected simply reverses the direction in which the loco runs and the runaway is now in reverse. All other locos, eight in total, operate perfectly. Any advice appreciated. Thanks, Mike