Thanks for the reply.
Here's what the manual says:
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During the hack process, your PhatBox will reboot itself several times. The general rule of thumb would be that it’s possible the PhatBox will reboot once for every hack it applies. There are currently 11 hacks that the hack process runs on your box, so expect it to reboot 11 times!
Each time a reboot occurs, and your headunit switches to a different source, please switch back to the PhatBox so that it can run the next hack.
When the hack is complete announcement, or you have waited a ridiculous time with no announcement, turn off your stereo and remove the DMS from the Phatbox.
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If it reboots just the once, then I think I'll risk it. I'm about to embark on a 7 hour drive to France with 2 kids in the back, so I'll wait until I get back
About the booting problem, yes it could very well be the cable. I bought a replacement cable from ebay as the phatbox was originally in an Audi A3 which was pre-wired. It's now in a Bora which was not, so I had to buy a 5m cable. I had to assemble the end myself so there's a good chance there's a dodgy connection!
I also read that to fix a booting problem, you should disconnect the phatbox cable and re-connect it to cause the HU and box to re-handshake. I tried this and there's no difference. Another site mentioned that the cable should be earthed or you will get booting problems. There is an earth break out cable on the cable I bought from ebay but I've yet to find an unpainted earth point to connect that, so that could also be it.
If anyone has got any other theories, please chuck them in the pot!
Thanks
Andy