The early MRM Sources had an LED on the front to indicate 33 and 45 rpm. Due to the strange way it was done the platter would occasionally start cogging when ostensibly switched off with the switch in the centre position. Mike's solution was to either ignore it or switch off at the plug (or the power supply if you had a 3D, which of course he had).
On the later Source-Odyssey models I redesigned the circuit and omitted the LED so that the switch actually disconnected the psu. A number of owners have revised their early decks to eliminated the LED. Using the existing components it is not possible to have both the LED and the disconnected psu without changing the switch to one with an extra gang such as a rotary switch. An alternative is to wire in a second switch to switch the feed from the power supply.
To get an idea of the options and what is involved in changing the wiring, here is a description of the wiring layout in the early Source. Photos of his deck, courtesy of Rob Cole.
The early MRM decks had a bicolour LED at the front. These AC PSU decks had a full wave bridge rectifier (the little black box on the motor board) near where the wires from the power socket at the bottom of the photo, enter at pins 4 and 5. They could also run on DC from the bigger supplies such as the 3D. The wires near the round capacitor are pins 6 and 7. The group of three and the group of two grey wires are heading to the switch. The three are for the speed change and are actually coming from the far edge of the board, pins 1,2,3, passing under the motor.
The LED was fed from a little circuit mounted on the switch which was powered from pins 6 and 7. See photos and circuit schematic Fig 1.
The LED had three wires one for each colour and a common.
There was no switching on the supply side, so the deck was prone to cogging when the switch was in the middle position (the notional "off") as this also switched off the speed setting, leaving the motor without a reference.
The cogging can be avoided by switching off at the power supply or mains socket.
The later decks had no LED, and a DC PSU connected to pin 6 (via the switch) and to pin7. One gang of the switch switched the motor board speed connections, and the other gang broke the supply to the motor when in the centre position, like the Fig 2.
If you are rewiring the deck to eliminate the LED, take care with the motor board solder points, as they are fragile and the pcb tracks can lift and break. It is best to leave them and use the existing wires which are already soldered to the board. Doing it this way has the added advantage of not needing to remove the motor, which can be a pain. See schematic Fig 2.
The safest procedure is to first unsolder the LED wiring from the switch, leaving untouched the group of three grey wires connected to the speed change pins 1, 2, and 3 on the motor board (top three in the photo below).
Remove/ de-solder the components (resistors and transistor), leaving only the group of two grey wires. Solder one of these, together with a short insulated link, to an outside tag on the switch (where the purple wire is in the photo above,) and the other to the centre tag of the switch )where the white wire is. Solder the other end of the link to the other outer tag of the switch. Don't forget to solder this link across the switch.
Then at the input socket unsolder the wire on the round pin of the two pin DIN (the power supply wire which goes to pin 5), leaving it still attached to the motor board.
As close to the motor board as you can, snip off the group of two wires which supplied power to the LED. Then take one of the two grey wires returning from the switch, strip the end and solder it to the DIN. Solder the other end to the wire going to the motor board, insulating with heatshrink sleeving.
Unless you use a different 3 position switch with an extra gang, eg a rotary switch, it is not possible to have the two colour LED.
You could have a single colour to indicate on/off if it is wired in parallel with the switched supply i.e across pins 6 and 7. See schematic Fig 3. In this case you would desolder the wire at the round pin of the DIN, and leave the group of two grey wires from the LED uncut at the motor board as is.
The components and LED would be left in situ and the wires to the switch disconnected (white with green stripe, purple, green) at the switch. Then connect the old centre wire (white with green stripe to whichever of the LED wires you have just disconnected from the outer tags (purple or green) to get the colour you prefer.
You would then have to run two new wires, to replace the two grey ones in the non-LED circuit (Fig 2). One from the centre tag on the switch, to join the wire to pin 5 that was
previously disconnected from the DIN and one from an outer tag at the switch to the DIN. At the switch, a link would be soldered to
between both outer tags.
If you wish to add an extra switch to isolate the input from the power supply, insert it so that it breaks the circuit from the psu input socket to the motor board - which are the two wires, grey and grey/black on the left of the picture.
Any questions, drop me an email.
Note that wiring colours may be different in decks of different ages.
Below is my original sketch. The top sketch is the later dc version with either DIN or XLR sockets. Ignore the rest...
