SONY TC-K850ES: Producing a M4066BP Replacement
With the help of a bit of simple reverse engineering of the original TC-K850ES schematic, I have produced a solution based on a miniature relay and a command transistor. There is nothing fancy about this circuit. But I wanted to build it on a miniature printed circuit board that will be equipped with augat pins with a raster identical to a 2 x 7 pin integrated circuit. Like the original M4066P circuit.
Here is the schematic. Please note that this is *not* a universal *4066 replacement circuit. It is targeted only to TC-K850ES deck. It will probably work with other similar Sony decks that use the same signaling and voltages. But this needs to be verified before attempting to use it.
The trained eye will spot the fact that I chose to command the relay using the inverted command signal (/CMD) that appears on selector pins 5 and 6 of the integrated circuit. This is done in order to keep power consumption at minimum while in play mode. The relay coil will be energized and the armature will commute only when the MONITOR switch selects LINE IN as the monitoring signal source. Should the MONITOR switch select TAPE as a monitoring signal source, the relay coil will not be energized and the mobile armature will be idling. Thus this circuit will draw close to 0 mA in play mode.
And the two layer miniature printed circuit board layout.
Bill of materials.
|C1||100 nF / 50 V||X7R dielectric||80-C322C104J5R|
|R1||10 kΩ / ¼ W||carbon film||291-10K-RC|
|REL||A-18W-K||low profile, small signal||817-A-18W-K|
Now I am waiting for the printed circuit board that I ordered at a factory in U.S.A. that does extremely cheap prototypes. This PCB went for $ 3.95, free shipping. This is way cheaper than if I had done it myself.
Here is a link to the project on OSH Park: SONY TC-K850ES M4066BP Replacement
For fun, here is my simple reverse engineering page. There are a number of errors -- like relay pin numbering -- in my hand drawings. But who cares? I have corrected them all in the final circuit presented above.
Disclaimer: This circuit is provided AS-IS. In no event will I be liable for any damage whatsoever arising from the use of this circuit on your cassette deck. Please note that this is not a general *4066 circuit replacement and it cannot be used directly in place of any *4066 integrated circuit in any arbitrary position within a cassette deck, or other similar equipment. This relay switching circuit was designed exclusively for the SONY TC-K850ES deck alone. Its conception is the result of reverse engineering the audio and control signaling implemented in the original electrical schematic of this cassette deck.