Model Power MRC 4-4-0 Need Help

[CBQ Fan]

I run DC on my layout and have one of these little buggers.  While running it it came to a sudden dead stop and I can smell burnt electronics. I have absolutely no interest in DCC and sound does little to nothing for me. Is there an easy way to ditch the DCC circuit board and just run straight DC?  I really don’t care if the headlight lights up as my prototype did not run with the headlight on during the day.  I just want to be able to fire it up on rare occasion.  I got a steal on this and don’t want to have buy a whole new one or pay to install a DCC board when I don’t need it.  And please don’t try to convert me to DCC.

[Jbub]

Having never seen the inside of one I don't have a solid answer for you. But, if they used standard dcc wire colors then black to gray and red to orange is all you'll need. Rip everything else out and you'll have a straight dc loco with no lights

[peteski]

Looking at the very nice writeup and photos on Spookshow's site ( http://spookshow.net/loco/mp440.html ) Jbub's advice is on-the-money.  Just cut out the decoder and connect red to orange and black to gray wires.  That will power the motor directly from the track with no headlight.

I'm curious at to what brand and model of DC throttle were you using when you let the magic smoke out of the decoder?

[CBQ Fan]

Tech 4 260

Thank you guys!

[brokemoto]

I have several items with the so-called "smart" decoders, including the MP/MRC eight wheeler.  I am a DC guy, as well.  One thing that I did notice about the MP is that it DOES run much better on the MRC 2400 with pulse OFF than it does on the 2800 or the TECH 7,  It runs best on 2400 with pulse OFF, next is the Kato, followed by the TECH7 with the 2800's bringing up the posterior.  I have not tried any others on it (such as the 2500 or any of the 1400 series). 

Some have posted that the pulse can confuse the decoders or do other things to it.  I did see this on the B-manns on the 2500.  In fact, I would set the direction one way and the B-mann went the opposite.

The only decoders that I have fried on DC were several of the B-manns.  It was mostly on the 2800, but there was one or two on 2400 with pulse OFF.  What is funny is that some, but not all, of the B-manns  run markédly better on DC with the decoder gone.

[peteski]

What is funny is that some, but not all, of the B-manns  run markédly better on DC with the decoder gone.

That is perfectly normal and expected.  You are eliminating a complex electronic device between the rails and the motor. A decoder running on DC does not take itself out of the motor circuit - it is still controlling the motor.

Decoder passes the usually unfiltered or pulsed DC track voltage through its rectifier and uses that to power the microcontroller, which then tries to power the motor through its PWM motor driver, relying on that pulsing DC as the power source.  It is far from optimal. Motor receives a pulsing DC voltage further chopped up into PWM pulses.  In addition, the pulsing DC can sometimes confuse the microcontroller into "thinking" that it is seeing DCC packets.  This all can add up to poor running quality when using standard DC throttle.

The decoder would run better if the DC track output voltage was filtered in the throttle. Then it would be similar to what the decoder sees (out of its bridge rectifier) when it runs on DCC.  Taking the decoder out of the circuit is beneficial for DC running (when unfiltered pulsed DC throttles are used). And by "pulsing DC" I don't mean the "pulse" feature of some more advanced throttle.  Pulsed DC is simply unfiltered DC that most throttles supply to the track.  Full-wave rectified voltage coming from standard throttles has 120Hz pulses (even though the throttle does not have "pulse" feature.  The "pulse" feature usually eliminates every other pulse of the 120Hz peaks, making the DC pulses more pronounced.  Using that feature is even more detrimental to the DCC locos running quality (since that creates larger gaps in DC voltage pulses for the decoder to deal with).

[CBQ Fan]

Looking at the very nice writeup and photos on Spookshow's site ( http://spookshow.net/loco/mp440.html ) Jbub's advice is on-the-money.  Just cut out the decoder and connect red to orange and black to gray wires.  That will power the motor directly from the track with no headlight.

I'm curious at to what brand and model of DC throttle were you using when you let the magic smoke out of the decoder?

@peteski  That fix worked perfectly!  Thanks.  Now it looks like one of my BLI E7’s is biting the dust.  It is now smoking and starts to run slowly and then shuts down.  Any thoughts on fixing this?  I am not switching to DCC, so that is out. I wonder how these shells mount on a Kato E chassis. 

[peteski]

@peteski  That fix worked perfectly!  Thanks.  Now it looks like one of my BLI E7’s is biting the dust.  It is now smoking and starts to run slowly and then shuts down.  Any thoughts on fixing this?  I am not switching to DCC, so that is out. I wonder how these shells mount on a Kato E chassis.

You are welcome Brian. Actually, Jbub was the one who proposed the procedure, I just verified and agreed with him

You can remove a decoder from pretty much every model, But with the E7, it will be a bit more complicated. If you are not afraid of tackling some basic N scale electrical work, you can easily remove the decoder and wire the model to run on DC.  If you want to also have the headlight working, that would be a bit more advanced.

Take the the shell off and remove the decoder. If the wires are terminated by connectors on the decoder, don't cut the wire too close to the connector - leave some wire to make it possible to reconnect the decoder if needed. Then find the left pickup wires from the trucks (one from each truck) and one of the motor leads, and solder the 3 wires together. Insulate the joint with a piece of heat shrink tubing, electrical tape, to some other insulating material. Do the same for the right side pickups and the other motor lead.  If the loco runs backwards, swap the motor leads around.  That's all.   If you want to wire the headlight, that would be more work and likely require purchasing additional components (a capacitor, resistor and a diode) and few more wire connections.

[CBQ Fan]

@Jbub   Thank you also!

[CBQ Fan]

You are welcome Brian. Actually, Jbub was the one who proposed the procedure, I just verified and agreed with him

You can remove a decoder from pretty much every model, But with the E7, it will be a bit more complicated. If you are not afraid of tackling some basic N scale electrical work, you can easily remove the decoder and wire the model to run on DC.  If you want to also have the headlight working, that would be a bit more advanced.

Take the the shell off and remove the decoder. If the wires are terminated by connectors on the decoder, don't cut the wire too close to the connector - leave some wire to make it possible to reconnect the decoder if needed. Then find the left pickup wires from the trucks (one from each truck) and one of the motor leads, and solder the 3 wires together. Insulate the joint with a piece of heat shrink tubing, electrical tape, to some other insulating material. Do the same for the right side pickups and the other motor lead.  If the loco runs backwards, swap the motor leads around.  That's all.   If you want to wire the headlight, that would be more work and likely require purchasing additional components (a capacitor, resistor and a diode) and few more wire connections.

Are there any other decoders that would be plug and play?  Sound or no sound either way.  I guess I could contact BLI and see if they sell replacements, but if I am going that route is there a better choice?

[peteski]

Are there any other decoders that would be plug and play?  Sound or no sound either way.  I guess I could contact BLI and see if they sell replacements, but if I am going that route is there a better choice?

If you are thinking any of the industry standard plug-n-play decoders (like the 6-pin NEM connector or similar) then no.  BLI decoders are made specifically for their models and while the wiring harness uses connectors (not soldering) to attach the wire harnesses, those connectors are proprietary to BLI.

Spookshow's website has a good writeup about these models. http://www.spookshow.net/loco/pcme7.html
If you bought the DCC/sound equi[pped model, it uses their proprietary decoder and harness.


But if you bought a second run of E8s set up for DC then it appears that they do have an 8-pin plug-n-play connector for a universal decoder (no sound).


But again, if your model was sound-equipped then there is no standard DCC connector in it.  Are you confused yet?   

[CBQ Fan]

Well, it looks like I will be calling BLI to order a replacement decoder.  I will have to talk to them about my power supplies and see what they have to say.  These units seem to run fine alone, but multi units lead to all kinds of issues. 

[CBQ Fan]

Or do I gut it and make a dummy out if!   

[peteski]

Or do I gut it and make a dummy out if!   

Or just gut it to make it into a DC loco (follow my earlier instructions). Should not be *THAT* difficult to splice few wires together.

[CBQ Fan]

Or just gut it to make it into a DC loco (follow my earlier instructions). Should not be *THAT* difficult to splice few wires together.

I am not sure if I want to invest that kind of time into it.  I have a bunch of these. I also do want the headlights to work. I am wondering if it is my power supplies.