Puzzled About Decoder


D&J RailRoad

D&J RailRoad

Professor of HO
Now I'm stumped.
I've been messing with this MTH SD70ACe all day tryin to get a decoder into it.
The motor works when I connect a 9volt battery to it.
The decoders work. I've tried two ESU decoders and one Tsunami but they won't drive the motor. I get sound but no drive. 1 ESU and 1 Tsunami are right outa the wrapper. The other ESU is from another loco that never worked well, brass drive train problem.
The LokProgrammer can see and program the ESUs. My Decoder Pro JMRI can see and program the Tsunsmi. I don't get voltage at the motor leads but the sound increases motor RPMs and sounds horn. Test each decoder on my Loy's Toys decoder tester shows motor voltage increase when decoder is connected to it.
I checked for grounding of motor to the chassis but it's fully isolated. I can see motor leads all the way to motor.
Yeah, test track is clean as it programs and sound is present.
Wires are correct because sound is present and responds to throttle on loco address.
Same lack of drive using three different decoders.
Somehow I'm missing something.

20220523_202953.jpg

The picture below shows the decoder attached to the decoder tester and throttle set to forward at 25. Pilot light on tester is lit next to forward.
20220523_211556.jpg
 
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Try setting cv19 to 0, and see if that helps.It's possible the throttle has that engine number in a consist, and the motor won't run unless the lead address tells it to. Even if this doesn't work, it's not going to hurt anything to try.
 
As I illustrated in the picture, the throttle is dialed up to the decoder address 9370 and the forward light on the tester gets brighter as I advance the throttle speed. That indicates that the motor leads are producing electricity to the motor. When I hit reverse, the reverse pilot lamp illuminates indicating the motor is turning the opposite direction.
This decoder is from another loco but I set it to factory default before installing it. The other two decoders act the same way so I doubt very much that all three would have somehow toggled themselves over to a consist address, all the same number but then respond to a 4 digit address.
 
Have you probed the DC output from the board to the motor with a multimeter? I'd be curious to see if you're getting juice there just to rule out the wiring from the board to the motor.
 
When the decoder is wired to the loco there is no output from the DC side of the decoder. When I disconnect the DC leads, there is voltage. Only found this on the decoder in the picture. Haven't checked it on the other two decoders.
I thought there might be a short from the decoder or motor to the chassis but there isn't.
 
Talking to a former MTH dealer, he says he thinks there may be a small capacitor within the motor design. This will represent a short to the decoder which in turn will make it shut off the DC output.
I'll check this out tomorrow. A cap should be visible by inspection.
 
I took the motor out of the chassis then connected the DC leads from the ESU decoder to it while the input to the decoder was through the Loy's Toys tester. The motor would just start for a split second then stop. The tester showed a short. I disconnected the motor from the DC leads and connected my volt ohm meter. DC voltage came up as I increased the throttle. Back to the motor, short. I replaced the ESU decoder with the Tsunami decoder, same events.
My conclusion is: The MTH motor is designed to work specifically with the MTH decoder. All other decoders won't match up to the load characteristics of the MTH motor.
Obviously another market capture design built into the model so no other decoders could be used in the model other than MTH.
I'm trying to fit an Athearn Genesis motor into the MTH frame but the chassis will need some extensive modification to do so. The drive shafts will need to be replaced as well. Not sure if there is a drive shaft available that will fit the truck gear boxes and the Athearn flywheels.
MTH designed their models in an effort to capture the HO scale market in a manner that only their DCS system could be used along with only their repair parts. Wondering why they went under? not a very well thought out system. RIP MTH, you deserved it.
 
Interesting. Did you see any capacitors? I still think it's a plausible culprit.
 
Reading this thread, got me to do a little research, found a whole load of stuff (most of which was gobbledygook to me) re: DCS/DCC and non working decoders thought these might be worth a look at, it may help or not.

KB1016: MTH Decoder Reset

www.digitrax.com www.digitrax.com

 
They say it runs on DCC which is true but trying to MU it with other DCC locos doesn't work so well.
I run most of my trains MUd so the MTH gets left on the shelf.
 
This is what the MTH loco ended up as, a dummy. The motor won't work with DCC decoders. The LED lights aren't compatible with NMRA compliant decoders. I'm surprised the wheels aren't a different guage than standard HO.

20220530_205444.jpg
 
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