Drone won't take off after upgrade - steps to troubleshoot

[monoJoker]

Hi all, I'm brand new to drones and recently bought a used AR Parrot 1 to try out. The seller claimed to have upgraded the bearings to low friction and the rotors to carbon fibre units. However I only found out after the sale that he'd never flown it since the upgrades. I'm following the instructions on takeoff and the front of the unit lifts a few inches but the back doesn't, then it slowly moves backwards - from the thrust of the front lift but won't take off to the 1m hover height as the manual says it should.

Now I realise it could be caused by a few things and googling lists anything from the rotors being installed incorrectly to bent shafts, etc, etc. Given it flew (so I'm told) before the upgrades and that's all that has been done to it, what would be the first things to check? I'm hoping it might be something obvious that the previous owner stuffed up when "upgrading" it

If anyone has tips before I start pulling things apart and possibly going down a very deep rabbit hole with no idea I'd really like to hear them.

TIA

[AR.Tommy]

Hello and welcome,

could also be caused by the motors or bend propellers. I would recommend checking the propellers first, also if the order is right.