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Only runs in one direction

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  • Member since
    November 2022
  • 1 posts
Only runs in one direction
Posted by Golfingtrain on Tuesday, November 29, 2022 12:41 PM

Just purchased on ebay a P2K SD7 locomotive. On DC voltage it will only run in one direction. If you turn it around it still only runs in one direction. It still has the original light board and it does not appear that any components are burned out. Apply direct DC voltage to the motor it runs fine in both directions. Has anyone run across this before? The light board does have the 8 pin jumper for DCC decoder. Thanks.

  • Member since
    February 2008
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Posted by maxman on Tuesday, November 29, 2022 5:31 PM

When you say that it runs only in one direction, do you mean that it runs the same direction when you turn it end for end, or does it run in the opposite direction?

For example if it runs to the left initially and you turn it end for end, does it still move to the left or does it then move to the right?

  • Member since
    November 2002
  • From: Colorado
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Posted by fwright on Tuesday, November 29, 2022 5:39 PM

On DC, the locomotive always runs the same direction on the track unless you reverse the polarity of the DC to the track.  Turning the lcomotive end for end does not change the direction it will run on the track.

Fred W

  • Member since
    August 2003
  • From: Collinwood, Ohio, USA
  • 15,162 posts
Posted by gmpullman on Tuesday, November 29, 2022 5:52 PM

Check the DCC jumper plug to be sure it is seated in the socket properly. You could try reversing the plug end-for-end and if the engine now runs in the other direction but not the direction it did before then there's something wrong in the continuity of the jumper (or dummy) plug.

For some reason I've kept all the old light boards from past DCC installs. Pretty sure there's a couple L-L SD boards in there somewhere:

 DCC_PCBb by Edmund, on Flickr

If it turns out you have a bad trace/solder connection or diode I can send you a spare. IF you plan on installing a DCC decoder the best bet is simply remove the light board and hard-wire a decoder in its place.

This site has good photos of the original light board and dummy plug:

https://drupal.tcsdcc.com/installation/ho-scale/1419

Good Luck, Ed

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Posted by jjdamnit on Tuesday, November 29, 2022 6:13 PM

Hello All,

maxman
When you say that it runs only in one direction, do you mean that it runs the same direction when you turn it end for end, or does it run in the opposite direction?

OK, here's a basic (stupid) question...

When using your DC Cab (controller) are you selecting "Forward" or "Reverse" to change direction of the locomotive (track polarity)?

The National Model Railroad Association (NMRA) standard is, "...that locomotive moves forward when the positive rail is on the right."

If the movement is in the opposite direction, select "Forward" on the cab and switch the track feeder wires.

Golfingtrain
Just purchased on ebay...

There is a possibility that the previous owner reversed the polarity from the wheels to the motor to intentionally run this unit "reversed" in a consist.

An extremely unlikely scenario is that the motor has been only wired to run in one direction despite track polarity. This is possible with DC but very unlikely.

Hope this helps.

"Uhh...I didn’t know it was 'impossible' I just made it work...sorry"

  • Member since
    February 2002
  • From: Mpls/St.Paul
  • 13,192 posts
Posted by wjstix on Thursday, December 1, 2022 11:33 AM

Ed's comment about the jumper is quite likely to be the issue. I can see a situation where the original owner ran DCC, but then decided to sell the engine so removed the decoder to use in another engine and plugged the DC jumper plug back in, but got it reversed 180 degrees. 

Otherwise, if you're for sure only going to run it on DC, you can just remove the lightboard and wire it like 'the old days' before lightboards - connect the pickup wires from the right rail to one motor lead, and the two from the left rail to the other motor lead. 

Stix

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