A small breadboard (100*33 mm) salvaged from another old TV set.
It features three RCA female sockets (the standard yellow, white, red) and a 3.5 mm jack female socket (black).
A Google search has produced no meaningful result for these marks.
A snapshot of the schematics:
Composite Video (yellow RCA jack)There is nothing on this side, other than a diode: if it were a Zener (but I do not see any mark for that) it would protect the next stage from peak voltages; if it is a standard diode I do not understand its function...
Audio (input, red and white RCA jacks)
The audio channels are identical with a low-pass RC filter with extra components. As per the simulation, the cut-off frequency (70% of peak incoming voltage) is around 2.3 MHz, which is in line with what is mentioned in my previus RCA blog. (The result is the same for the simple RC circuit calculated on a spreadsheet).
Pin 9 acts as detector: when there is no jack the path 8-9 is closed with continuity; when the jack is introduced the circuit is open. The same happens with pins 3 and 6, but only pin 9 is connected to the rest of the board. (Because of this, when the red jack is in, the resistence between pins 8-9 is 150 ohm).
Audio (output, 3.5 mm black jack)
The jack is a standard 3.5 mm TRS.
This part of the board is also symmetrical: J1 is ground, J2 and J3 are the audio channels, J4-J8 and J5-J7 are detectors, J6 and J9 are unused pins.
If there is no jack, none of the internal contacts shows continuity; when the jack is in, there is continuity between pins 4-8 and 5-7.
The circuit is a low-pass filter with a cut-off frequency (70% of peak incoming voltage) of less than 0.3 MHz - a bit on the low side as per my previous blog on RCA boards.