Oh, the 'I took it home already' feeling. I had a really bad case of this last week, bought a 17 KW solar inverter for a relatively small amount of money and lugged it home, all 50 Kg of it. It worked when it was taken off the wall according to the seller, but on plugging it in on my end it didn't work, though the display lit up and it seemed to work it wasn't making any power. Normally you'd return it as defective and that would be that but this thing is heavy and it was far away.
Long story short: the seller was a trustworthy fellow and definitely did not try to pull a fast one on me. What happened is that during assembly in the factory or a later repair someone smashed the lid into the main circuit board, almost but not quite tearing off one of those IDC headers for flat cable. Bits of it were rattling around in the case which already had me suspicious upon unloading it. That must have been quite the impact, those things don't normally break. The vibration of the transport across 200 km in a car with a stiff suspension did the rest and dislodged the cable completely. Plug the cable back in and it still worked, so I guess I got really lucky. It's been on the wall and has been making power for the last 3 days without any errors.
Long story short: the seller was a trustworthy fellow and definitely did not try to pull a fast one on me. What happened is that during assembly in the factory or a later repair someone smashed the lid into the main circuit board, almost but not quite tearing off one of those IDC headers for flat cable. Bits of it were rattling around in the case which already had me suspicious upon unloading it. That must have been quite the impact, those things don't normally break. The vibration of the transport across 200 km in a car with a stiff suspension did the rest and dislodged the cable completely. Plug the cable back in and it still worked, so I guess I got really lucky. It's been on the wall and has been making power for the last 3 days without any errors.