Here are several problems and solutions for a V2 recorder. I suppose they're fairly common because they're related to bad design.
One or both headphone channels go intermittent or quiet:
=> There's a small daughterboard with two inductors which is soldered to headphone jack left and right pins. I took out the jack and glued it down, IIRC with a tiny bit of epoxy. I put in short component leads into the holes by the pins in order to reinforce the solder joint and I resoldered the daughterboard.
Charging jack is intermittent:
=> The charging jack is apparently mounted on its side! The PC board pin for the centre pin has been rotated and the pin for the side connector is connected via a short wire. The connection between the wire and pin was the problem. The jack would probably benefit from some epoxy too.
Apparently worn out battery:
=> The battery contacts inside the unit suck. Clean all contacts and make sure the ones inside are not bent. You might not need a new battery.
Won't turn on to charge battery:
=> Apparently in order to charge the device needs enough battery power to turn on first. I charged the each battery half 50 ohms off 5V for a few minutes, checking the voltage often. (Might be better to use <4.20V through a lower value resistor.) After this the device could turn on to the charging screen when I plugged in a charger and charge normally.
Breaks at solder tabs holding the board to the metal part of the case:
=> I've reinforced these with bits of component leads and desoldering bread. I'm not sure this repair is good enough because they broke and copper can pull off the board. However, someone else was using it during that time so I don't know how what it went through.