I've checked all the soldering, especially for the ribbon connectors and that all looks clean and solid. Cat 6A cable of around 3m used for the first test.
Any pointers on fault finding will be much appreciated.
Latest firmware installed and works fine with the standard radio, not sure if there is a setting in the menus I should be looking for?
First bit of debug - powering up the pico with usb power does give me the "MD9600 remote head" message - good start! Which i guess means I should look at power supply to the head first.
Not 100% sure what the issue was, I re-seated the ribbon cables and tried a new extension cable and we were away. Went back to the first extension cable and that's fine too. So I'm guessing one of the ribbon cables was the issue.
On first use it does have a couple of quirks around processor noise with FM squelch open and the volume control is kind of 'stepping'. I'll use it for a while and see how it sounds in use on digital.
Thanks guys for the work you've done to get this up and running.
I am not sure why it didn't work first time. The raspberry pi pico in the head has to 'remember' the power on/off state, and this has to be in sync with the state of the main processor. It could be that takes a few power cycles to get correct.
The MCP4023 volume control chip only has 64 possible settings, so the volume control will move in steps. If you normally use the radio in a quiet environment you could change the zero ohm resistor on the radio board to a larger value which would reduce the maximum volume and spread the 64 steps over the lower range.
Noise pickup is down to the way TYT designed the front panel, the ground connection is shared by the audio and the display. Fitting the volume control chip at the radio end of the cable reduced the noise pickup. However the ground is still common through the short ribbon cable to the radio. On my radio the noise is barely noticeable but that may vary between radios. The ribbon cable has some resistance so it might be worth adding a short extra wire directly from the radios ground to the ground of the new PCB.
Yes, unfortunately the background processor noise on receive on my radio is very high, to the point of annoying on DMR. I'll experiment a little with earthing as you suggest and see if I can improve it any. I've also found the maximum volume to be somewhat lower with the remote head - but I've also done the mod to tame the rather sensitive volume control on the standard radio so that may have some impact as well.
I think as you suggest it did take a couple of cycles to sync the radio and remote, although the initial problem must have been no power as I would have expected the the MD9600 remote head message even if nothing else worked?