Having replaced the TNC and the U/S aerial, I was still baffled as to why G0ROZ-3 did not appear on www.aprs.fi.
The station was Digipeating and sending out beacons. Looking at the paths of stations that had been digipeated, G0ROZ-3 was shown in the packet path. Even so, aprs.fi was not showing packets being digipeated.
After some research and digging around, I found that the station ID had been set to G0R0Z-3 (Golf Zero Romeo Zero Zulu dash Three). Checking with aprs.fi showed all the beacon packets under the callsign G0R0Z-3.
I must have set it to this when I took the new computer up to site.
So wearing my embarrassed face, I took on the holidaymaker traffic and took another trip up to site. Callsign has been changed to G0ROZ-3 and all is well with the world again (Touch Wood).