Non-invasive GD-77 debugger connections

I wanted to connect a hardware debugger into another of my Radioddity GD-77s, but didn’t want to drill a hole in the side like I did on one of the radios…

But I then realised that the rubber protector that goes over the 2 jack sockets in the side of the radio, can be removed, and this gives a handy hole, through which I can feed the Serial Wire Debug wires.

Inside the radio, the wires are soldered on 4 pads on the back of the main PCB, roughly in the area between the # and 0 buttons on the keypad.

To prevent the wires either breaking off where they are soldered or worse, pulling the pads off the PCB (which is a common problem), I have used hot glue to secure the wires close to where they are soldered to the PCB

Taking the GD-77 this far apart is relatively easy, as its actually only held together by 2 screws near the base of the radio, and also by the 2 ring nut’s around the SMA connector and the volume / on/ off knob.

The 2 obvious solder pads just in from the 2.5mm jack socket are the speaker connections, which I have temporarily unsoldered as the wires to the speaker are very short.

The white and black connector on the left in the photo is for the flexible ribbon cable for the display / keypad PCB which screwed to the front of the radio.

To detach the ribbon cable, you have to separate the black part of the connector from the white part, using a small flat blade screwdriver.

The trickiest thing when re-assembling the radio is re-inserting the ribbon cable and then pushing the black part of the connector across so that it crimps the ribbon in place.

But I’m becoming a dab hand at doing this as I’ve repaired server GD-77’s for members of the local radio club, where they received GD-77s where the ribbon cable was not securely clipped or the cable was not pushed in far enough, so that over time the display became partially disconnected.

BTW.

Some eagle eyed readers will notice that I pealed off the Radioddity logo, because I wanted to see if anything was underneath. As you can see, nothing is…

It may however be fun to make another label to replace the Radioddity one, but I’m not sure yet, the best way to do this.

Another small note…

To erase the CPU, it needs to be halted by the debugger, which requires the Reset pin to be connected. In my case that’s the purple wire.

However once the CPU has been erased once, the Reset is no longer required, so I could in theory open the GD-77 again and remove that wire.

But Its not causing too much hassle at the moment, so I simply leave it disconnected, or connect it via a resistor to +3.3V from the debugger, to prevent RF pickup on the reset pin which can cause the radio to reboot if you transmit with 5W, or sometimes even with 1W!