The RFOFF is an RF modulator replacement that improves the composite and S-Video output from the Commodore 16 and plus/4 and adds a few quality of life features. Not only are jailbars, checkerboarding and noise significantly reduced or eliminated, edges are enhanced without unwanted ringing.

Feature summary

• Compatible with both PAL and NTSC
• Vastly improved S-Video and composite output
• S-Video jack replaces the old RF output
• Configurable 3.5mm output
• Chroma attenuated to 300mV as per the S-Video spec
• Adjustable luma:sync ratio (contrast control)
• Improved signals also available on the A/V DIN connector
• Fully assembled and ready to install (plus/4 version requires installing pin headers - see below)
• Optional luma bypass mod that further reduces checkerboarding and jailbars with S-Video

Install

C16 version - Desolder the original RF modulator and solder in the RFOFF.

plus/4 version - Desolder the original RF modulator and solder the extra long pin headers into the mainboard, making sure the pins are straight. Install RFOFF onto the pin headers with RFOFF tilted down towards the front of the machine (tilted up towards the rear). Screw the mainboard back into the lower case and align the s-video and 3.5mm jacks with the case holes. Once you have the jacks aligned correctly with the case, solder the pin headers to the RFOFF and cut off any excess.

If using the optional luma bypass - remove the TED (the big 48pin chip), install the luma bypass board and insert the TED chip into the bypass board - be sure the notches on the sockets and chip are aligned. Connect the mini coax cable from the bypass board to the RFOFF, making sure the int/ext luma jumper on the RFOFF is OPEN.

If not using the optional luma bypass - make sure the int/ext luma jumper on the RFOFF is CLOSED.

Setup

3.5mm Right Channel Switch

Set the selector switch to the desired "right channel" output. A 3.5mm to 2x RCA cable or splitter is recommended

External: Left channel is audio, right channel will be whatever is connected to the "input" header.

Dual Mono: Both left and right channels are mono audio.

Composite: Left channel is SID audio, right channel is composite video.

Remember audio signals can be safely spilt, but not video signals. You can for example use the 3.5mm jack for composite video on the right channel, and split the left channel audio into left and right (dual mono).

The board can also safely drive both composite and S-Video outputs at the same time but not dual S-Video or dual composite (using both the RFOFF outputs and A/V DIN connector). In most cases you shouldn't need to use the A/V DIN connector, but all the improved video and audio signals will be available there if required.

Note chroma from both the S-Video and A/V DIN connector is attenuated to 300mV - this conforms to the S-Video specification but will also work fine with Commodore monitors that use separate luma/chroma.

Contrast fine tune

Commodore used a fixed value resistor in their RF modulators which don't take into account variances in the video output of each and every TED. I've added this option so the output can be tailored for your TED and display combination.

To find the ideal value for your TED and display combination, first set the potentiometer to the mid position and power on the computer. Adjust the potentiometer until the white foreground becomes a very light grey, then turn it slightly in the opposite direction stopping when the foreground is pure white.

Note this adjustment may have little to no effect depending on your display or upscaler - in which case it is recommended just to leave the trimpot at the mid position.