Hi,
It was a bit random. it would often say -1666 or just some other random numbers every few seconds. I read somewhere (I think on EEVBlog) that the 7106 shows 1666 or something continuously if the oscillator circuit is faulty. The analogue input voltage to the chip seemed stable and reasonable depending on the range and voltage applied at the meter input. The 7106 is in a pluggable socket so I decided to try swapping it, cost about $16 delivered. That fixed it. The display always worked OK though, so not really the same fault as you seem to have, but it might still be worth swapping the 7106 if you don't find anything else amiss. That's just a suggestion, I'm not an expert at all.
I can put some pictures of the PCB up, either here or link it to a similar new post for info on my particular meter. It uses a plastic velum with conductive "zebra" stripes between the 7106 and the LCD, yours seems to be different in design there. The YF-1100 is all built up on the same top PCB side as yours though, the Voltcraft 6010 has components on the bottom side which is interesting.