Control & Electrics
Sorting out the wiring – Connecting panels and boards
As originally built, the layout consisted of ten boards with the eight scenic boards are individually connected via multi-pin plugs to the main control panel. On each board, droppers from the rails and point motors were soldered to wires run to tag strips on the edge of each board. These in turn joined with wires cabled together, suspended underneath each adjoining board and run to a multi-pin plug with socket on the main panel. This wiring ‘structure’ seemed to be a well designed arrangement and generally the board wiring looked in reasonable order considering the layouts age, journeys and storage.
Tag strips with wires cabled, routed and labelled.
32 way extension cable passing entering cable duct under door
Following their visits I came up with a plan.
1) Make some legs for the main panel, position it and arrange for the power supply.
2) Repair the plugs and sockets so that each board will connect to the main panel.
3) Construct a new panel for the loops.
4) replace the existing controllers and power supplies.
5) start documenting the wiring and update it as repairs progressed.
6) Service and repair the point motors and check that the points operate.
7) repair track feeds.
An issue arose because I had created the lifting board across the doorway, where previously a fixed board was wired directly to the main panel via a cable attached to one of the 32 way connectors. This cable now wouldn't reach the main panel without blocking the door so it needed extending and re-routing. The 32 way plug and socket connector was made by McMurdo and amazingly after 50 years are still available on Ebay...although not cheaply. I bought a plug and socket, a reel of wire and proceeded to solder up a 4m, 32 way extension lead to reconnect the plug on board 1 to the socket on the main panel. This was practical because when building the shed I had made a cable duct across the doorway for just this issue.
Having set up the layout and arranged the panels and wiring as best I could, I was reluctant to switch on in case any unnoticed short circuit should cause further problems. The few bits of significant wiring damage needed an understanding of how the system worked prior to repair so would have to wait until more knowledge was gained. For a few weeks I Just poked around checking things out and making notes. When I thought I knew the questions which needed answering, I asked for help from members in the North West area group of the 3 mm Society. Frank Allen and Alex Larsen came over one day and between them deciphered the push button system for the loops control. On another day, John Carter and David Garner came and uncovered the secrets of the main panel and point control system. Without their help I’d still be scratching my head so thank you Gentlemen.
Main Panel (MP)
The main panel was fixed on legs made from an Ikea shelf unit and the old H&M Duette was replaced by a Gaugemaster controller providing power for two walk around's for the up and down main lines, the Goods yard and point motors. The panel connects to the boards by 163 wires through 11, 9-way plugs & sockets and two 32-way connectors. Some plugs were broken so were repaired with Epoxy and a couple of the multi-pin cables had been pulled from the tag strips but they would have to wait for repair until the panel was working to find out which wire connected with which tag. Some of the plugs were labelled so I completed that in anticipation of documenting the plugs.
Plugs to main panel
Main panel with new controllers
So we now have the boards set up, connected to the main control panel which is also on legs with new controllers. onto the return loops!
Loops panel.
The control panel for the two return loops boards, consisted of two separate pieces of chipboard which would have originally been fastened to the layout and was hard wired to the baseboards. The first job was to fasten the two parts of the panel together and create a new control panel ‘module’ to slot between the upper and lower loops boards. This picture shows the two parts of the board and the wires after I had attached labels at both ends prior to separating them.
The home made controller and power supplies were stripped out and replaced with a Gaugemaster transformer powering an old Digitol Twin electronic controller plus a Capacitor discharge unit for the point supply.
Rather than continuing with the direct wires between the panel and the boards, I had decided to divide the two to make repair and maintenance easier and to keep with my theme of making the layout a little more ‘movable’. I first traced each of the 70 plus wires and labelled it with self adhesive numbers at each end, prior to cutting it. I then re-wired the cut ends to tag strips or terminal blocks installed on the panel and baseboards, before joining the tag strips with SCART connectors.
This completed the first four parts of the plan with the boards, panels and cabling in position. I felt I now understood how most of the layout should work so was able to make a detailed list of the tasks required to finish repairing the wiring on the boards and the main panel and led onto the documentation.
An A4 folder was set up with file dividers and plastic pockets. Firstly I wrote a general overview of what I’d discovered about the wiring, then drew a plan of each board with a track plan noting each track section number and turnout number. There is a section for the multi pin connectors and a section for the wiring record sheets. The idea is that just from the folder you can follow a wire from its physical baseboard ‘asset’ through its tag and terminal its connector and to its ‘actuator’ on the panel. Each board was numbered, 1- 10. Then each tag strip was lettered A,B,C etc. then each terminal was numbered. I drew up and photocopied ‘Wiring Record’ sheets. For each wire these set out which board, tag strip and terminal it was connected to, then where it connected FROM and where it connected TO plus any notes. The 'from' shows Multipin (plug) #5 terminal 6
At this stage I took each board down in turn. I arranged some temporary ‘legs’ bolted through the securing holes in the end frame so I could work on the underside of the board. This allowed me to mark the wiring parts using a marker pen and following each wire I could note its start and end points and what it did. Start assets were things which were operated, like point motors and track sections. Therefore point motors became PM1 – PM51, track became Up, Main Outer (rail) or Cattle Dock inner.
On the panels the connectors were already numbered so I drew a rough sketch of the plugs and sockets and numbered the terminals. The wires from the sockets went straight to one or more ‘Asset’ such as a switch. Wires between tag strips and sockets would be noted as running from terminal 1 on the socket to 3 B 4 meaning board 3, tag strip B, terminal 4
This is quite a job but working methodically through it means I now have a full record of what each wire does and so understand how Ralph originally designed and operated the layout. It also allowed me to check every joint and fix any defects.
Sorting out the wiring – Turnout operations
The layout is fitted with 51 Hammant and Morgan SM3 point motors. These venerable beasts are familiar to many railway modellers and represent fine examples of simple, solidly built British electro-mechanical engineering. Still working after half a century, most of them required little in the way of tinkering before carrying out their sober duty of moving the tie bar. A dust with an old paint brush and blow through to remove any dust was all that most needed. Some had seized so received a dose of 3 in 1 and a few had to be removed, stripped and serviced but all eventually responded to the 16vac from the old Duette.
As originally designed the points were operated by power from the duette being taken into the control panel to a rotary wafer switch set into the track plan. The switch knob showed which route was selected and the power was directed down one of two wires going to the respective coil. Despite the SM3’s renowed ruggedness, they got a poor reputation because of the unreliability of the built in switch. On Exeter Central, this switch was used to cut off power to each coil after changing. It meant that quite often the power didn’t get to the coil in the first place so the turnout didn’t move. It was going to be far too much trouble to easily access each motor to fix what was likely to be an ongoing problem, or to fit a micro switch in place of the built in one. The answer came from David Garner who suggested I investigate a device from MERG (Model Electronic Railway group) which could easily bypass the switch and provide a local CDU to improve the operation of the whole unit. ..The PD3
There are some 27, PD3 units which are built from kits in about 20 minutes each. They are installed close to each switch machine and operate from a dedicated 20vdc supply. This supply is a laptop power supply bought on Ebay and is wired into the existing 16vac point power circuit. The PD3 works on a different principle to the original wiring so some modifications to the switching was required.
Point motors as originally wired
Point motors wired via PD3's. Note the reduced amount of wires
The 16vdc system requires a separate wire to each coil from a switch on the control panel. The PD3 requires a single wire from the switch and is either ON or OFF. This means that one wire from the switch can be discarded. A downside to this system is that when power is turned off, the switch wires then return to OFF and some of the points change. They don't automatically reset when power is reapplied so when a layout is returned to, many of the point switches need flicking to match the point position...annoying, but at least the points work reliably now.