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Dapol Signal gets the Merg treatment


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A club colleague asked me to advise and help with the electrical side of his new N gauge layout. It is based on Prince's Risborough and includes part of a 'heritage' branch line. He purchased a couple of Dapol motorised signals for the branch line. Now, Dapol came up with a curious control system for their signals, requiring an AC power supply to a red and a black wire, and a push-button type switch connected to two yellow wires to cause the signal to move from its current position to its other position. However, without looking at the signal, it is a matter of luck as to what position the signal will end up at on pressing the button.
 
Being a member of Merg, I knew that a kit was available to replace the Dapol control circuit with a more conventional one, that runs from a DC power supply and can be controlled by a simple on-off switch, or a DCC accessory decoder. However, I would not class this kit as a beginner's one, so I volunteered to do the conversion. This kit includes some very small surface mount components, but with a little care and attention, it all went together without to much trouble, and both signals worked first time. As with all the Merg kits, the conversion kit comes with clear and detailed, well illustrated instructions. With the exception of the range of Pocket Money Project kits, Merg kits also have the smaller components attached to a card, clearly labelled, which helps to ensure the correct components are installed in the right place. There are also some spares of the smallest components for losing in the carpet. I had already added some components to the PCB when I took this photo.
 
post-11458-0-82505500-1506513136_thumb.jpg
 
Because the instructions are so complete, I will not simply repeat them all here, but will just show some photos to give an idea of what is required to be done.
 
Here are the main components of the Dapol signal once dismantled and the wires disconnected.
 
post-11458-0-74229300-1506513125_thumb.jpg
 
Of course, fitting small surface mount components to a PCB requires specialist equipment. Mine consists of a piece of wood, a wooden clothes peg, coffee stirrers and cocktail sticks (toothpicks).
 
post-11458-0-41655900-1506513152_thumb.jpg
 
An important, and slightly tricky, task is to remove the limit switch contacts from the old Dapol PCB, and attach them to the new PCB in the correct place. These can be bent slightly for final adjustment to ensure the motor stops at the correct positions for the signal.
 
post-11458-0-95178400-1506513140_thumb.jpg
 
Final assembly is pretty much the reverse of the disassembly, but you must ensure the actuator arm from the motor worm will locate between the limit switch contacts.
 
post-11458-0-15328300-1506513146_thumb.jpg
 
And then, test it still works:

https://youtu.be/04R6SujMtNo

 

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