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Fabrication guidelines
These are the recommended steps to fabricate the board with your own
- Get the latest revision of the fab files https://github.com/yeokm1/graphics-gremlin-hdmi/tree/main/fab
- All the gerber files for PCB fabrication are inside the Zip file
gg-hdmi-rev-X.X-gerbers-drill.zip - These are some settings to use for fabrication:
- Size: 106.4 x 95 mm
- Thickness: 1.6mm
- Minimum hole size: 0.3mm
- Surface finish: ENIG recommended to protect the ISA fingers. Hard gold if you can afford it.
- Copper: 1 oz is sufficient
- Min track/spacing: 6/6mil
- For assembly, you can either assemble it yourself or outsource it to your fabricator. I have used the service from PCBWay and they did it reasonably well. Just submit the BOM to them
gg-hdmi-rev-X.X-bom.csv. Should automated assembly be required, the component position filegg-hdmi-rev-X.X-top-pos.csvis also available. For pin headers, it is not strictly required to follow the ones provided in the BOM, feel free to use any breakaway pin headers you have.
The circuit board is a 2-layer board, 4.19 x 3.74 inches (106 x 95mm). No special edge connector bevel is required, but you may want to specify at least ENIG plating. If you are rich then you could spend the extra money and get hard gold plated edge fingers. Order the boards with a fancy soldermask color so you can show off, or stick with a plain green to blend in.
You probably shouldn't attempt this project if you've never soldered surface mount components before. It'll lead to a lot of frustration and potentially damaged boards and parts.
There are two main methods you can use to assemble the board: reflow and hand soldering. Using the reflow method means that you'll need to order the solder stencil for the top side (there are no parts on the bottom of the board), and be sure to have fresh solder paste and some sort of vacuum pick-and-place tool. This method can be very quick but does require some skill and practice.
Hand soldering is good when you only want to assemble a single board. This board has no BGA or leadless components which makes hand soldering possible. Some components have a very fine lead pitch (0.5mm) so only attempt this if you are comfortable with your soldering skills.
No matter which method you use, I recommend inspecting every solder joint very carefully under a microscope to make sure there are no solder bridges. If there are, clean them out with some solder braid.
Be careful not to mix up the two voltage regulators: they provide different voltages!
R11 should not be stuffed. By default this means that the 14.318MHz clock is generated on board. If you move R25 to R11, then the 14.318MHz clock comes from the ISA bus. The motherboard's 14.318MHz oscillator isn't always accurate enough for CGA color composite video.
Header J6 is optional. If you want to install it, remove pin 2 for keying.
Before plugging the card into a PC, it is wise to use a multimeter to verify that there are no short circuits between the +5V line (ISA bus pin B3) and ground or between the +12V line (ISA bus pin B9) and ground.