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Asssembling the LumaFix64 1.2sp

LumaFix64 is a hardware mod for the Commodore 64 that allows you to reduce banding artifacts such as vertical bars. It was developed by e5frog at the Lemon64 forum, and version 1.2sp is Sven Petersen's revision of the original design.

It is available pre-assembled or as a kit from various sources, including from the AutumnHippo store. If you acquired the kit, or if you're sourcing the parts yourself, here's a short guide to assembling the mod.

Required Parts

If you aim to source everything yourself, Sven Petersen's GitHub page supplies you with the gerber files for having the PCB produced, as well as a BOM list for the required components. Below is an overview for easy reference, for full details please see Sven Petersen's BOM list.

  • 1 x PCB rev 1.2sp
  • 1 x DIP-40 socket
  • 2 x precision round pin headers, 1x20 pins
  • 2 x SMD capacitors, 47 pF, 0805 (C1, C2)
  • 1 x SMD capacitor, 100 nF, 0805 (C3)
  • 3 x potentiometer, 2k ohm (AEC, PHI0, CHR), one of the three potentiometers is optional (CHR); only if you desire chroma adjustment
  • 1 x Hex inverter 74HCT14D, SO14 (IC1)

Assembling

Assembling the LumaFix64 1.2sp requires basic soldering skills, including
both through-hole and surface mount soldering. For the latter, I use a hot-air
reworkstation without problems, but you can also use a reflow oven if that
works better for you.

Generally, soldering the board is relatively straight-forward. However, since the board is pretty small, and some of the parts are located "inside" the DIP40 socket, I would highly recommend soldering the parts in the following order:

  1. Begin with soldering the surface-mount parts below the DIP40 socket: IC1, C1, C2, C3. Make sure that the HCT14 is oriented correctly, so that the notch marked on the board silkscreen is lined up with the notch in the chip. If the chip has a marking, showing the location of pin 1, that marking must be in the same end as the silkscreen notch.
  2. Place the two pin strips from the bottom of the board, and solder them from the top.
    • Make sure to place the pin strips between the white lines, as seen from the bottom of the board.
    • Before soldering, make sure that the pin strips sit in a 90 degree angle to the board. This can be done by placing them in a solderless breadboard while soldering.
    • Also, make sure that the wider part of the metal pins sit against the board.
    • After soldering the pin strips, snip off as much as possible of the excess pins above the solder points, in order to allow as much space as possible for the DIP40 socket. However, don't snip the solder point itself, and keep the remainder of the pins roughly equal in height.
  3. Place the DIP40 socket from the top, and solder it from the bottom. The socket might sit slightly at an angle, but the important thing is that it rests against something on both sides: On one side against the board, on the other against the snipped-off pin strip solder points/pins.
  4. Solder the potentiometers. You may omit the chroma pot marked "CHR" and replace it with a solder blob (or a resister at R1). According to Sven Petersen, "The Chroma potentiometer is IMHO not required, because it is not desirable to reduce the chominance level before the composite video signal is generated in the RF modulator".

Using the LumaFix64

After installing the LumaFix64, you will likely find that the picture is now much worse. That is completely normal. Now it's time to adjust the three small screws on the potentiometers. Start with the one closest to the edge of the board, and when you get the best picture possible, move on to the next one. Please note that each potentiometer screw may turn many, many times, and at first nothing may seem to happen. There are many descriptions of the process available online. For example from Breadbox64, Lyonsden, Mark Fixes Stuff or Retr0rob.

Please be aware that we are working with analogue technology, and a perfect result is rarely possible. The artifacts will not disappear completely, but one may argue that they are a nostalgic part of using original hardware, as long as they are not too invasive. Making them not too invasive is what the LumaFix64 can do in most cases. In fact, your results may vary (a lot!), depending on both the specific graphics chip in your C64, but also on your specific screen. Some people see a much more profound result than others.