Second opinion - suspect I've blown a decoder

[tbdanny]

I recently purchased two Bachmann Spectrum 2-8-0's in N scale.  After installing a DZ125 in each one, I discovered that one of them had a short that blew a motor winding.  I was able to get a replacement mechanism, as the crank pin split after 10 mins of running.

After transplanting the decoder from the broken mechanism into the new one, I have discovered two oddities.  The first is that the headlight is about half the brightness of the 'good' loco's headlight.  The second is that the loco with the replacement mechanism will initially start creeping along nicely, up to mainline speeds.  However, after a few minutes of running, the motor in this loco stops responding.  I am still able to switch the headlight on and off with the appropriate function button.  However, the only way to get the motor to respond is to cut the track power for several seconds, after which it will return to normal.  I suspect the decoder may have been damaged, but these symptoms don't seem to match many other decoder blowouts I've heard of, and would appreciate it if anyone could provide a second opinion on this.

Thanks in advance,

tbdanny

[locoi1sa]

  How did this loco run on DC? Was it tested? I would suspect a thermal sut down of the decoder is happening. The headlight being dim could be a CV being set at constant dim instead of full brightness or a resistor that is too large. If the decoder programs and you are able to read CVs on the program track than I would think the decoder is functioning properly.

        Pete

[rrinker]

 A motor winding shorting out could very likely kill the motor driveon the decoder, but it wouldn;t be likely to have an effect on the function outputs. You potentially could program and read back with the motor drive being partially blown. Try testing on DC, if you can put a dummy plug in place of the decoder. Check the current draw and see if it runs smoothly on DC.

                                   --Randy

[tbdanny]

I broke both locos in on DC on my club's layout before installing DCC in them - after loosening the motor screw, they ran smoothly. I have tried a decoder reset on the problem chip, and reloaded it with the previously programmed CVs. Everything is identical between the two locos - mechanism, CVs, light boards, wiring. Could it possibly be a bad solder join between the loco frame and the decoder?

[jeffrey-wimberly]

 If you suspect a bad solder joint then check it out. If the problem persists you'll have to replace the decoder. I've had a couple of DZ125's do the same thing (flaky motor drive and weird light functions) because of motor shorts in an Athearn switcher. I replaced the motor and the switcher stopped eating decoders.

[Hamltnblue]

At this point I would just send it to Bachmann.  They have an excellent warranty and the charges are minimal.  More info here.

http://www.bachmanntrains.com/home-usa/service.php