WS19 No1 MkII control unit help
 

I have a No1 MkII control unit for my WS19 that the fuse holder on the inside has broken. Would someone please send me a schematic, or better yet, a photo so that I can repair mine? I also seem to be missing the power light at the top, unless this unit is just supposed to have a plug at the top. At the moment I’m unable to upload any photos via my iPhone. Thanks much.

I might have a schematic but will have to search a bit. Here is an exploded diagram and parts list.

Hi James,

There's no light on a No.1 control unit - only on the "Operator" ones (2, 3, etc.) where it is the "A set unattended" warning lamp and operates if none of the headset selection switches are in the "A set" position. (This is done by having one set of contacts on each headset selector switch pass pin 10 on the harness straight through the box unless the switch is not in the 'A' set position.) The control unit with only a single 12-way connector (No.1, 1A, 5, 8, 12, 13, 17 or 33) had the switch connected via the fuseholder to earth (control unit case).

The set supplied 12 volts on pin 10, and the Operator's control unit (No.2, or 3 series) had a lamp holder and resistor in series with pin 10, so that if pin 10 was connected to earth in any of the control units (because all the headsets were connected to the Intercom or 'B' set) the warning light would come on to alert the operator that nobody was monitoring the 'A' set..

In smaller vehicle installations, the No.1 or 1A (or equivalent) control unit was used on its own, and the fuse had to be removed in order to prevent a short circuit of the 12V supply when the headset selector was moved from the 'A' position. (The 250 mA fuse was fitted to prevent smoking the wiring if this was forgotten.)

The hole in the side of the No.1 (or equivalent) Mk.2 control unit is next to a 4-way connection strip for the Driver Intercom wiring (Mic, Phones, Signal and earth) for use with the later Junction Distribution No.3 and/or No.4. (Mic is IC Amplifier input, Phones is IC Amplifier output, Signal is the 'Call Commander' buzzer output to the intercom circuit.) The hole is normally plugged with a blind rubber grommet if not required.

Best regards,
Chris.

Thank you. That helps quite a lot.