The RFOFF is an RF modulator replacement that improves the composite and S-Video output from the Commodore 64 and 128 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.

Note the original Commodore 64 longboard (ASSY 326298) is not compatible but there are some simple mods that can also improve the video output of this revision.

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
• Optional luma bypass mod that further reduces jailbars and S-Video checkerboarding
• Optional HDMI (DVI) output for the large VIC-II Kawari (longboard version only)

Install

Desolder the original RF modulator, insert the RFOFF into the mainboard but do not solder it in yet. Install the mainboard into the case and make sure the rear ports line up correctly with the case. Once you have confirmed the alignment is correct, remove the mainboard and proceed with soldering the RFOFF in place.

Luma bypass

Comparison and install video

If using the optional luma bypass - remove the VIC-II, install the luma bypass board and insert the VIC-II 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, otherwise you will not get any video output.

For pre V1.1 boards, please see below for the old luma bypass instructions

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 SID audio, right channel will be whatever is connected to the "input" header. The most common use for this would be dual/stereo SID setups or LumaCode. For example if used with LumaCode, LUM from the VIC-II-dizer would connect to "input", and GND to "ground".

Dual Mono: Both left and right channels are SID 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 composite and S-Video outputs at the same time but not dual S-Video or dual composite (using both the RFOFF output 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. Aftermarket C64 S-Video cables may have a 300ohm resistor in series with the chroma output, this should be bypassed when using the RFOFF. If using Sven Petersen's AV adaptor the "CHROMA HI" jumper should be closed.

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 VIC-II. I've added this option so the output can be tailored for your VIC-II and display combination.

To find the ideal value for your VIC-II and display combination, first set the potentiometer to the mid position and power on the C64. Change the foreground colour to white (POKE 53281,1) and adjust the potentiometer until the white foreground becomes a very light grey. Then turn 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.

Longboard HDMI

This option will only work with the Large VIC-II Kawari that outputs a DVI signal over a micro HDMI connector. While this does replace the S-Video connector on the RFOFF, both the S-Video and composite output on the A/V DIN will still carry the same improvements to video quality as the other versions.

This version includes a male micro HDMI to plug into the Kawari, a flat flex cable, and a female micro HDMI port mounted on the RF replacement. To install the flat flex cable, first make sure the locking tabs (the little black plastic piece) is open, then insert the flat flex cable with the contacts facing up into the connector and close the locking tab.

It is highly recommended to confirm the HDMI output from the Kawari is compatible with your display before ordering as the Kawari does not output a standard resolution. Please also keep in mind this is a DVI signal, as such it does not carry audio, you will need to use either the 3.5mm jack or A/V DIN for audio.

Luma Bypass (pre V1.1 only)

This mod requires cutting the luma trace at both the VIC-II end and the RF modulator end and substituting it with a piece of shielded wire (included) running directly from the VIC-II to the RF modulator. As this is more of an advanced mod it is assumed you have some idea what you are doing, and are willing to accept the risks (and a couple of cut traces).

First you will need to find the luma trace from the VIC-II and RF modulator. This will be coming from pin 15 on the C64 VIC-II or pin 17 on the C128 VIC-IIe and connected to the 2nd pin from the right on the RF replacement (when looking at the topside of the board). Be sure to do a continuity check between these points before cutting any traces.

Once you have confirmed continuity you will need to find the actual trace from the VIC-II. This is different for all boards and may be on the top side or under side, it could also run under the VIC-II socket so make sure you know which one it is before cutting. Take a deep breath and cut that trace. There, that wasn't so bad eh? Now do another continuity check to make sure the trace is cut, and that you've cut the right one. Now cut the RF modulator end. This will always be on the underside of the board - 2nd pin from the left when looking at the underside.

Strip around 1cm of the outer sheath from on end of the shielded wire and twist the wire into a point. Then strip 0.5cm of the inner wire and tin both.

For longboards Connect the inner signal wire to the RF modulator luma pin and the shield wire to the nearby post holding the RF modulator.

For Shortboards and C128 Connect the inner signal wire to the RF modulator luma pin and the shield to the pin next to it (3rd from the left when looking at the underside of the board).

Route the wire over to the VIC-II luma pin avoiding running it between IC pins or any component pins as these can easily pierce the outer sheath. Once you have a rough idea of how the cable will be routed, trim off any excess.

For the VIC-II end you only need to connect the inner signal wire. Strip the outer sheath but this time fold the wire back over the cable, use the heatshrink (included) to cover any exposed shield wire while leaving the inner wire sticking out. Strip the inner wire, tin, and solder to the luma pin for the VIC-II (pin 15 for C64, pin 17 for C128). Check continuity between the VIC-II and RF modulator and also make sure there are no shorts to ground before powering on.

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