Hi, I shorted out two digitraxx dcc decoders today, I was trying to install them into an athearn gen F7 B unit(which ran fine in DC), but after placing the shell back on and running it, the decoders mysteriously tripped the circuit breaker and then died permenantly.
I think there’s something wrong with the motor, and its insulation with the metal chasssis…or a bad motor. I now converted the b unit into a dummy.
Anyways, what I was curious was, does anyone know which specific part of the decoder motherboard absorbes the short circuit impact(and needs to be replaced)? Anyone with an electrical engineer degree?
If the track power cam in contact with the motor drive side (ie, you didn’t insulate the motor from the grounded frame on older Athearn locos - always double check this and it helps to be double safe and not only put a layer of Kapton tape (not gooey electrical tape) in the frame below the motor, but also swap the motor clips top to bottom so the one with the tab that rubs the frame is on top and can’t wear through the tape - just don’t let the brush springs and brushes fall out), the component that gets fried is the motor driver IC. There may be some other passives around it that get fried too. If you’re lucky, it didn’t get back to the microcontroller outputs that drive this. If those get blown as well, it’s a completely lost cause, because while you might be able to replace the components, you have no way of getting the firmware that goes in the microcontroller to actually make it work. Digitrax, TCS, and others will give you a one time warrnaty replacement even if it’s your own fault it fried. But just once, so make sure the motors are isolated before installing the replacement decoders.
The standard method for bringing up a new decoder, even for an experienced modeler is to bring it up first on a programming track. This will use a low powered signal to protect everything. Did you do this?
The part that usually “goes first” is faulty wiring.
The safe position inserts a 27Ω 2watt resistor in series between the power supply/DCC controller and the decoder/locomotive to prevent dinging anything.
If I change the road number on the engine, or any other CV using the programing track, can I immediately activate the horn, bell or make it move forward or backward, without backing out of the programming track mode?
Randy - The engine was dcc ready as it was genesis. The motor shouldve been isolated.
Beasley - I wasen’t aware of this, but both decoders I used were used previously in other engines and worked fine. Also this seems incredibly tedious, atleast to me. Since you literally cant test anything(speaker, lights,motor) except reading CVs. Call me stubborn.
Henry - thats the thing, Im not sure, its very interesting. The engine with decoder worked fine previously. I took it out of storage for a few months and suddenly when I placed it on the track and set it to speed step 1 my powercab read a short, and the loco was no longer responsive after reseting. So I think its something more to do with a faulty motor.
Hi, this was helpful.
I’ve traced the motor leads to first entering the a 506V(- lead) and 561U(+ lead) chip before entering some resistors and both into an (1Ft) chip then entering into the main chip (16F690)
The 506V and 561U are probably the power controls, the Micro processor is the 16F690. I will get some pictures of the digitraxx decoder boards up tomorrow.
there’s no direct communication from the decoder to the command station. to read CVs, the decoder pulses the motor to draw more current which the command station monitors. the command station won’t be able to read CVs if the decoder can’t drive the motor.
if the processor is OK and the address known, the decoder should be able to turn the LEDs on/off.
i thought all decoders use a single h-bridge chip that connecs to both motor leads. there should be 3 (maybe just 2) connections between the processor and h-bridge. if it’s the h-bridge chip, you could replace it
No, you have to exit program mode first. Like the PowerPro, track running is disabled when in programming mode. Compounded by the PowerCab only having one set of outputs that serves as both the main track and program track.
No system can run a loco on the program track, with a few special cases - the Digitrax Soundloader software with the PR3 or PR4 can run a Digitrax sound decoder, sounds only, on the program track but only because the Digitrax sound decoders have a CV that disables the motor drive but allows the sounds to play. This CV corresponds to the master volume on some Tsunami decoders so you don’t want to try that with any other decoder.
The point of using the program track first is not to do the full setup, but to see that you can read and write CVs. If the motor has connections to the track because it’s not isolated, programming will fail, but the lower current of the program track will hopefully not fry the decoder. If programming on the program track works, you can be reasonably confident that there is no wiring error, because the motor at least has to be correctly wired for programming to work. You could still have a function hooked up wrong, or a missing resistor for an LED that could damage the decoder on the main, but at least the motor circuit is known good at this point.
Ah shoot, you’re right about that. Let me wire some lights to the decoder to see if they work. I had no lights on the decoder previously as it was a B unit, so I never considered testing it. I’ll let you know the results.
Decoders Top side:
Decoders bottom side:
Main microcontroller on decoders:
Motor controllers (mosfets?) on the diesel style decoder:
Function outputs indeed do work! Also the decoder does take CV inputs(I resetted the deocoder and it responded with addy 3), but cannot be read(as expected). Seems like I just need to find a few new motor controllers(the 6 pin chips for each lead) to get the decoders working once more.
Decoders bottom side:
