Hummm...... conventional channels as in not 800mhz? Or do you mean it can't track the trunk but can still decode 800mhz digital? Sorry if I am making no sense, I can do some programming but this digital stuff still confuses me.
The problem with the 800 MHz systems, conventional and trunk, is that they are in the process of being rebanded. All 800 MHz frequencies in the 866 to 868 MHz range are are being dropped down 15 MHZ. In other words, as an example, frequency 866.6125 would become 851.6125. The 785 is able to receive all conventional 800 MHz frequencies after they have been rebanded. However, with 800 MHz trunk systems, it will not trunk track them unless the 4th digit after the decimal point in the frequencies end in a 5. If there are frequencies in the system that have a zero as the 4th digit after the decimal, it will not trunk track it after the rebanding. At least, this is the way it was explained to me.
As for it decoding 800 MHz P25 digital, it will decode the P25 digital on all 800 MHz conventional systems. It will trunk track and decode the P25 digital for Motorola 800 MHz trunk systems as long as the frequencies conform with what I posted above with reference to the rebanding.
If an 800 MHz trunk system that you want to listen to has not yet been rebanded, you will be able to trunk track it and decode the P25 digital.
I hope I didn't confuse you here, but if so, post and I or someone else will try ot help.