Page 25 - May June 2020
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 only going to need to do this if you have a locomotive with an old open-frame motor; most modern motors don’t have particularly high current draw. If the loco has any sort of light control cir- cuitry such as a constant voltage circuit to operate 1.5v bulbs, say, you should also check that doesn’t draw more than the decoder functions can cope with. I have seen such a piece of circuitry in an On30 MMI loco that drew over 600ma, which would have been fatal for any decoder function circuitry; expensive if the decoder is a sound one!
I mentioned Blu Tack, not that you hold the decoder to the loco with it, but as
a useful tool to check available space. If you’re not sure of the space available in a particular location, stick a chunk of Blu Tack on the chassis, and put the body back on, pressing down, carefully, till the chassis is home on the body.Then pull it off again and look at the now squished lump of Blu Tack. Is it decoder shaped?
If so, then the decoder should fit in that space, if not, you’ll need a smaller de- coder, or you need to put it somewhere else in the loco. In the GS-4, I worked out that the decoder would easily fit beside the motor in the firebox area of the loco.
Now that you have the decoder and know where it is going to fit, you’re almost ready to start the install. But first, you need to check that the two motor terminals are isolated from the chassis. This is absolutely vital; failure
to do this will mean that the loco won’t work on DCC and will probably let the magic smoke out of the decoder, too. If the motor has two brush terminals with wires connected to them, you’re almost certainly OK. But if you have an older loco with an open-frame motor, you
may find that one brush is connected directly to the frame. If that’s the case, your best option is almost certainly to replace the motor with a modern can- type motor. Your model will run better and be quieter as a result.
In the next issue, we’ll take the GS-4 apart and go through the steps of installing the DZ126 in it and connecting it to the existing lighting.
Mick Moignard
   ROUNDHOUSE - May/June 2020

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