iPad 5 charges when powered off; testing data included

I have two iPad 5th generation tablets (data/GPS), one 10 W OEM charger and one 12 W OEM charger with many OEM lightning cables.

One of the iPads charges very slowly and only in a certain connection. I bought it used with this problem. It otherwise functions normally with normal battery life and battery % display is normal. I have not opened it but there is no obvious sign of damage. The charge port was cleaned by me but not much was pulled out. The contacts were lightly cleaned with IPA, no obvious sign of damage to the contacts is seen either. I haven't had any trouble syncing/backing up with iTunes. A DFU restore was also performed but made no difference.

Using a USB ammeter which also gives the state of the data lines, the following info was gathered. The ipad is approximately 55% charged during these tests. Similar results are found with the 10 W charger and combinations of charger/cable. The other tablet charges just fine with these accessories.

12 W charger; no device plugged in

A: 0A

V-: 0V

D-: 2.77V

D+: 2.76V

V+: 5.18V

Ohms: 999.9

Watts: 0W

12 W charger; faulty iPad powered on, same result if in sleep or wake state

A: 0A

V-: 0V

D-: 2.74V

D+: 0.07V

V+: 5.18V

Ohms: 999.9

Watts: 0W

note: Upon plugging in, the iPad briefly wakes up and displays "Unlock iPad to use accessories"; no charging icon is seen.

note2: sometimes the result of this test was:

A: 0.06A

V-: 0V

D-: 2.74V

D+: 0.09V

V+: 5.18V

Ohms: 86.33

Watts: 0.31W

with no "unlock" notification but still no charging icon

12 W charger; faulty iPad powered off after plugging in to charge (if I plugged the tablet in when it was powered off, it would power on)

A: 0.47A

V-: 0V

D-: 2.65V

D+: 0.21V

V+: 5.17V

Ohms: 11

Watts: 2.42W

MacBook Pro; no device plugged in

A: 0A

V-: 0V

D-: 0V

D+: 0V

V+: 5.03V

Ohms: 999

Watts: 0W

MacBook Pro; faulty iPad powered on but in sleep state

A: 0A

V-: 0V

D-: 0V

D+: 0V

V+: 5.03V

Ohms: 999

Watts: 0W

note: Upon plugging in, the iPad briefly wakes up and displays "Unlock iPad to use accessories" notification pops up

MacBook Pro; faulty iPad powered on but in wake state (screen is unlocked)

A: 0.95A

V-: 0V

D-: 0.16V

D+: 0.17V

V+: 4.86V

Ohms: 5.11

Watts: 4.61W

MacBook Pro; faulty iPad powered off

A: 0.47A

V-: 0V

D-: 0V

D+: 0.14V

V+: 4.95V

Ohms: 10.53

Watts: 2.32W

The results on the MacBook were similar for both iPads.

With the charger, the normal iPad charges like this:

12 W charger; normal iPad powered on but in sleep state

A: 2.00A

V-: 0V

D-: 2.65V

D+: 2.65V

V+: 5.13V

Ohms: 2.6

Watts: 10.1W

note: no notification pops up

12 W charger; normal iPad powered off after plugging in to charge

A: 1.89A

V-: 0V

D-: 2.65V

D+: 2.65V

V+: 5.13V

Ohms: 2.7

Watts: 9.7

It seems there may be a problem on the D+ line. It drops to low voltage when a charger is plugged into the faulty iPad. I think this then makes the iPad think it shouldn't draw much power. The best way to charge (0.5 A) is from a charger when powered off.

If this is definitely a tristar/tigris problem, I probably won't attack it myself but if you think this could be a connector problem then I may try to fix it myself.

Thanks for any help.