The composite video mod for the computer Microdigital TK-83 unlike the Sinclair ZX81 it’s more easier.

You no need to install the usual transistor with 1 or 2 resistors / capacitor. The transistor is already installed on the motherboard of the Microdigital TK-83, so just pick up the video signal as described in the picture.

I remind you that the output signal will be in NTSC standard for the Microdigital TK-83 produced in Brazil (PAL-M)

Autopsy:

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from Wikipedia:

TK83 was a Sinclair ZX81 clone made by Microdigital Eletrônica Ltda., a computer company located in Brazil.

The TK83 had the ZILOG Z80A processor running at 3.25 MHz, 2 KB SRAM expandable up to 64 KB and 8 KB of ROM with the BASIC interpreter and a Joystick port. The keyboard was made of layers of conductive (membrane) material and followed the Sinclair pattern. The video output was sent via a RF modulator to a TV set tuned at VHF channel 3, and it featured black characters on a white background. The maximum resolution was 64 x 44 pixels black and white, for graphic plotting. There were some special characters (shade patterns) useful for games and basic images.

Although being a ZX81 clone, the TK83 did not have the ULA chip from Ferranti, used in the former. Instead it was manufactured with a dozen of TTL integrated circuits, which resulted in a somewhat large power consumption. This could be noted as the computer’s case used to become quite hot after some minutes of operation.

source: wikipedia