Imported from GitHub: redhawk668/ZX81-Composite · commit cb44f04 · license GPL-3.0

Description

ZX81 Composite video with Backporch

README

ZX81 Composite Video with Backporch

This PCB provides composite video for the ZX81, it replaces the internal PCB from the modulator. For ZX81's with earlier type ULA's it generates a back porch signal.

It will work with the later 2C210 ULA. However, this ULA does provide a backporch signal, so the 555 timer chip is not needed and can be removed. It is based on instructions and schematics found on zx.zigg.net.

Billing of Materials:

Qty	Value	Component	Package	PCB
2x	10K	Metal Film Resistors	Axial DIN204	R1, R2
1x	68R	Metal Film Resistor	Axial DIN204	R3
1x	56R	Metal Film Resistor	Axial DIN204	R4
1x	10nF	Ceramic Capacitor	Disc 5mm	C2
1x	820pF	Ceramic Capacitor	Disc 5mm	C3
1x	82pF	Ceramic Capacitor	Disc 5mm	C4
1x	22uF	Electrolytic Capacitor	Radial 6.3mm	C1
2x	1N4148	Diodes	DO-35	D1, D2
2x	BC337	Transistors	TO-92	Q1, Q2
U1	NE555	Timer IC	DIP-8	U1

---

Usage:

Desolder the modulator case, remove the PCB and solder the new PCB in. Solder wires to the +5 volt input, video input and video output. Re-assemble the modulator case and solder it back on the ZX81 board. Connect video output with the RCA, connect +5 volt and video in with the correspending pads on the ZX81 board.