CX CARD: Direct Tap Mod
Do this mod at your own risk! If you aren't careful, you could ruin something (but that kind of goes for all of these mods really)
This mod is optional, but if you do this mod, you don't need to remove or add any SMD components except the big crystal.
This mod is not for the faint of heart, however, to be honest, this is my preferred method. When not modding cards to annotate instructions, this is how i do it. The reasons are:
- It is very quick and easy.
- It leaves very little to none, "unknown" elements. On one of my 0603 SMD mod attempts, solder must have flowed under the component and connected between the 2 pads on the PCB, making a short, it took a while to track it down.
- It allows the use of non SMD components for the termination, which are quicker and easier to work with (for me at least).
- Seems to imbue a slight SNR boost (could just be from the BNC mod though).
This mod requires the BNC mod: https://github.com/tandersn/cxadc-hw-mod/wiki/CX-CARD:--Replace-RCA-jack-with-BNC-jack but don't do the last step of that mod.
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VMUX 0 = C16 (unpopulated on white card)
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VMUX 1 = C53
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VMUX 2 = C11
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Determine which VMUX you want to mod. I prefer VMUX2 because with VMUX1 you still need to remove SMD C31 if using cards that have it.
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Using a small drill bit, BY HAND, slowly twist in a clockwise direction over the trace just before the DC blocking cap of your desired VMUX. You may want to practice on an old broken piece of electronics before attempting the actual mod. Example VMUX 2 only:
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Example VMUX 1 and VMUX 2 (note: i have yet to remove C31 in this picture, but i did after):
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Check and make sure there is no continuity after drill bit maneuvers from the DC blocking cap to the L# of that input.
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Clean the board, i use an old toothbrush, brushing away from CX chip.
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Solder a wire from the BNC connector to the "away from the chip side" of the DC blocking cap as shown in the pictures.
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If using an external T connector and Terminator, you're done!
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If not using external terminator, add a normal size resistor for termination, using values appropriate for your particular setup:
