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Some success at last


petertg

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It’s been some time now that I have been itching to update my blog. A few months ago I said that I had successfully digitized my old Wrenn City Class locomotive (though for some unknown reason I can’t locate the post now). This was true only in part. I did get it to run, but it only ran for a few feet (or should I say decimeters) and then stopped. The final result was that I spoilt two decoders. Then, when I tried to put it back into DC status further problems arose. An exchange of comments on the appropriate forum led to the discovery that the armature had gone dud. I obtained a rewound armature and a supermagnet, but still no joy, only smoke from the armature. Further tests revealed that the insulation on the front brush holder tube had failed, so when I reversed the feed wires, it did work as DC but, obviously, it was still not in a condition to fit a decoder since the only thing I had managed to do was to have an insulated rear tube and an uninsulated front tube, just the opposite of the original situation.

At this time my idea was to get some replacement tubes and insulation in case I irreparably damaged the front tube when removing it. I was not successful in getting replacement tubes so, finally, I decided to be brave and try and remove the offending tube and insulation myself. I first tried to make a sort of press with two strips of steel pulled together with nuts and bolts, but it didn’t work so I finally got a long enough and thin enough bolt to pass through the tube and forced it half way out by tightening the nut up on the bolt using a larger nut as collar to separate the head of the bolt from the end of the tube and allow space for it to come out and then I placed a small wood screw having a head of smaller diameter than the hole in the chassis in the tube and knocked the tube out with the thin bolt through the other tube. I then removed the old insulation, insulated the tube with insulation tape and replaced it (all of the above was preceded by an exchange of comments on the forum, with great help being obtained).

I then prepared a separate oval for DC operation and tested for current consumption and came up with some really exorbitant readings (as discussed on the forums). Following indications given on the forum I did a static test and found a stall current drain of 1.87A so I decided to go for a large capacity decoder (1.6A normal, 2.5A peak, probably much more than really needed). The chosen one was Zimo MX632, but then the problem was acquiring one. My local shop does not stock this make, one relatively nearby dealer said they did not stock this model, another did not reply to my request and there was a third which I had located and then could not find again, so I had to order from a UK source. I can now say that finally to-day I have got the thing to run digitized.

Also mentioned on the forum was that I had lost the tender drawbar and was kindly provided with information for making a replacement. I made one out of plastic, not having the material or the tools to make one from metal and I was given two dimensions for the distance between hole centres (42 or 43 mm). I went for 42 and now find that this distance is 1 mm short. I may be able to rectify. If not, I shall just have to make another one.

I am now working on a solution to my point motor control system (discussed elsewhere), having found a solution on the forum. It will entail a substantial reworking of the present wiring but I think it will be safe from my clumsy fingers.

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