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Recalcitrant Wrenn


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Please forgive me for being boring with insisting on the same theme, but I still can’t get my Wrenn loco to run properly. As collaborative readers of my previous topics (Rewiring a Wrenn, and Rewiring a Wrenn 2) will recall, with their help I had got to the stage where I had discovered that the insulation of the front brush holder tube had failed so, since I had previously insulated the rear tube, the only thing I had managed to do was invert the original ex-works situation, but when I also inverted the wiring of the brushes (see photo 1), the loco ran perfectly in DC form.

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Then, with some difficulty, I removed the offending tube, insulated it with insulating tape and refitted it. I then thought that with one brush connected to the pick-ups and the other connected to the chassis (See photo 2) the loco would also run in DC. But it does not. Can anyone tell me where I have gone wrong?

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Nothing wrong in theory, so you have a disconnection somewhere, check the brushes and springs are free to move, check for continuity, chassis to brush, brush to the other brush (proves they are in contact with the commutator) and other brush to pickups.

Keith

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Thanks for the comment. I have tested all the continuities and all are correct. I had another look at a Ron Dodd video and tested the armature as indicated, seemingly OK. The only incorrect thing seems to be that one end of the pick up wire does not always make contact with its wheel. Would this be sufficient for the motor not to run? In this respect I would say that I have placed a 9V battery against the other pick-up wheel and its opposite number and still no go, while I do detect current at the top end of the armature.

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Try your 9V battery directly on the brush holders, if it doesn't run there is a problem with the brushes, which seems quite likely as that is the bit you worked on.

Regards

Keith

PS. Check that the motor is free to turn by hand just in case there is some mechanical problem.

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Can you put it on track and try running a test lead from one rail to the appropriate motor brush. If it runs you know which side isn't connected. Otherwise test the other rail/brush.  As a last resort, connect both rails to the brushes.

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Hi all!

Before I read the last post I had done more or less that and found that when current was applied direct to the commutator on one side there were signs of life. I finally concluded that one of the brushes was not conducting, namely the front one, which was a bit of a bind to get out because on forcing out the tube to reinsulate it, I had slightly deformed the outer end of the tube and the brush would not slide out and I had to dismantle the whole motor for the nth time to be able to push it out in the middle. I fettled the ends with a nail file, cleaned the commutator with alcohol, reassembled the motor, switching the brushes around, placed the loco on blocks to take the wheels off the ground, applied current and, lo and behold, it worked! The next thing will be to see if I can properly fit a decoder without blowing it. Hattons have informed me that they have one that might fit the bill.

I thank you for all your help and advice and beg your pardon once again for boring you with my troubles.

Peter

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