Now, if this was a Topfield 5800/5810 and it was a couple of years old or more, I would start to worry about the PSU capacitors failing causing the voltages to go out-of-specification.
However, the Toppy's are not known for their good ventilation and, without the built-in fan of the Humax, the temperatures inside the case can be relatively high and prematurely age the poor quality capacitors originally fitted. The 5810 is particularly know for running quite hot as its case is physically smaller with poor vents.
Many of our Hummy's will be approaching a couple of years old now, so could this problem be manifesting itself here?
I have been lucky enough to be able to do a direct comparison between a Topfield 5810 and a Humax HDR Fox-T2 as I had them running side-by-side. The Toppy was considerably hotter to the touch and had already had the PSU capacitors replaced some time ago.
I have no idea of the cause of you problem BH, but I suspect that it will happen sooner or later.
This is all purely conjecture, but one possible cause I feel we will see going forward.