Wobblinwheel Posted April 2, 2015 Share Posted April 2, 2015 I have a MRC "tech 6" system that can be switched from DCC to DC with a push of a button. I usually have my DCC locos on electrically isolated sidings when running my few, old DC locos (and, of course, vice-versa). After having set all of my DCC engines to CV29= 2, which is supposed to "disable" the decoder's ability to recognise DC signals. right? Well, after leaving my two Hornby A4's (DCC equipped, DC "disabled") on "live" tracks, while running a DC loco. When advancing the throttle on DC, the A4's started to go NUTS! Rapidly jumping forward, then backward, then forward, etc. Is that supposed to happen? The A4's are both equipped with TCS "Keep-Alive" decoders. I will say I haven't tried this with other decoder-equipped for comparison. Have any of you seen what REALLY happens when you apply DC power to a "DC disabled" loco? I haven't until now, and I'm a bit surprised at what happened. Is this normal? Link to comment Share on other sites More sharing options...
Flashbang Posted April 2, 2015 Share Posted April 2, 2015 Unfortunately what you're seeing is the decoder with the dc turned off interpreting the dc as a DCC signal and the decoder not able to understand whats being readThis is caused by too much ac appearing on the dc coming from the controller or the dc controller is using PWM. Both can be seen as a 'DCC instruction' by the decoder. Link to comment Share on other sites More sharing options...
Wobblinwheel Posted April 2, 2015 Author Share Posted April 2, 2015 That certainly makes sense, considering this "all purpose" controller. Thanks! Link to comment Share on other sites More sharing options...
poliss Posted April 2, 2015 Share Posted April 2, 2015 Not normal, and shouldn't happen with the Tech 6. It may be faulty. Link to comment Share on other sites More sharing options...
Wobblinwheel Posted April 2, 2015 Author Share Posted April 2, 2015 This is a Tech 6- 6.0 (6 amp), I've just gotten the handheld back from MRC for repair/replacement as the speed control knob quit working. It's supposed to be "brand new". I hope it doesn't "fry" my old DC locos! It is fuse-protected at 3 amps, though. Link to comment Share on other sites More sharing options...
poliss Posted April 2, 2015 Share Posted April 2, 2015 Do you have an oscilloscope handy? :-) Link to comment Share on other sites More sharing options...
2e0dtoeric Posted April 3, 2015 Share Posted April 3, 2015 No sillyscope? Put an OLD speaker with a large resistor in series with the controller output, then carefully turn up the speed knob. If you hear a buzzing noise, the controller is putting pulsed volts out. If the buzz increases in pitch as you turn up the power, you have a variable mark-space output.If you just hear a plop as the power is turned on, you are getting 'clean' dc. You might see the speaker cone push in - or out - further, as you turn the power up.I said to use an old speaker, as you will possible fry it, or distort the voice coil, so it will be useless afterwards! Link to comment Share on other sites More sharing options...
Wobblinwheel Posted April 10, 2015 Author Share Posted April 10, 2015 Now THAT'S interesting... Link to comment Share on other sites More sharing options...
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