A friend of mine came to me with an interesting hardware mod request recently. He is very serious about security when it comes to cryptocurrency, and wanted to set up a totally air-gapped machine for doing key signing, among other things. For his hardware, he chose a Pinebook 64, as the hardware and OS are fully open sourced, therefore subject to more scrunchy by security-minded people. Because he wanted it to be air-gapped, he had initially gone the route of disabling the network adapters, but the fact that they were still physically only a few clicks away from being re-enabled, and internet-ready bothered him. So, we decided to physically disable the WiFi and Bluetooth completely, in order to be 100% sure that it stays offline.
The Pinebook computer is essentially a slightly different version of the Pine64 board Single-Board computer, plus a display, keyboard, battery, and other peripherals. Aside from the SD daughter board, all electrical components exist on the main board, such as the CPU, memory, eMMC, networking, etc. In most laptops, you could just pop out the PCI-E WiFi board to physically remove networking, but not here.
Referencing the Pinebook Wiki, I found they provide the Main board schematics, which was a big help. With the schematics, I found that the RTL8723CS chip being used for WiFi and Bluetooth has a “chip enable” on pin 2, which is required to be pulled high for the chip to be enabled. I knew removing the 100K ohm resistor “BR1” would cripple the chip, but unfortunately, I was unable to find a PCB component layout, so we had to rely on visually tracing. Thankfully, this one was dead-simple, being right next to the RTL chip.
Both main board shields lift right off, if carefully pried upward, but you only really need to remove the smaller one covering the RTL chip. Looking at the schematic, and matching up to the chip on the PCB, I traced “BR1” to be the left-most resistor on the top row inside the smaller shield. I initially tried using hot air, but the lead-free solder was putting up a fight, so I just introduced a little leaded solder with the soldering iron to both sides, causing the resistor to flee to board.
Upon booting into KDE, we found that the network and bluetooth devices were no longer available. If my friend ever decides to revert the change, we can put a new 100K ohm resistor. And if he later wants to make this feature switchable, the Pinebook case has plenty of space for a small toggle switch.