Should be "easy" to diagnose but my 710D has weak hydraulic randomly. Let's say im ready to dig, I try to lift the loader with the rear backhoe, won't work... I try a second tine, don't work... Third time, success! Try it again, it works! Try again, don't work... Really random. Can work 5 times in a row than don't work once, or twice or three times.. Curling the bucket will do that but Imo less often...
You just described my wife.
Serial number? When you are trying to boom down are you using only the boom down or in combination with another function? Boom down circuit relief is set much lower than other reliefs (and system pressure) and may not lift the back of the machine by itself. With that being said it should lift it with the loader bucket in the air but if your loader bucket is on the ground it shouldn't be able to lift it. Pressure checks would be the order of the day.
792766 is the ser. no. What amazes me is that it's random... Same goes with bringing the bucket forward when digging. It will not come forward a time or two then, the backhoe moves since the power is very high. As said, sometimes it works sometimes not so I guess the pressure is low than super-high. No pattern found
Sounds as a overpressure relief has some debris passing and hanging occasionally, easy enough to pull to inspect, may have a line decomposing in the circuits.
Where would be your starting checks? I have the "technical" manual and repair manual but some guidance would be great
Work it, find the common point of trigger to no function or what triggers back into function. Check the relief on that function as per the service manual component location. Anything lodged in it will be a dead give away, nothing in it then inspect for damage or broken pieces as the spring or seats.