Faulty dock, no screen. Charging, Signal and Switch OK

I tried to search for this forum about same symptoms as in title but didn’t find any solutions.
I have a switch which had charging problem and the reason was failed P13 which I replaced.

  • The dock pins looks fine under microscope.
  • The dock charges the switch normally ~14.6V/0.8A
  • TV recognizes there is a signal and the dock shows green light

These symptoms are same as problem with P13. However this Switch works fine on other docks.

Are there any typical reasons for a dock not to show any output screen?

Does this dock in question work with another switch attached?

Nope. I think the dock failure damaged the P13 on its Switch.

Then it’s likely a dock fault, you could connect a breakout board to the dock and take diode/resistance reading to confirm. If there is a fault present, then it’s possible it could cause damage to a switch that is connected.

This is a good tip. I don’t have a female type breakout board but I used a spare part USB connector. There are two lines which should be OL but instead give some diode Voltage values. I’ll update photos and values later.

I checked the hdmi with breakout board they are good.

Here are the values from a working dock. I have checked that ribbon and port is fine by swapping them to a working board. So the fault has to be in the dock motherboard

The faulty lines are A2 and A3, they should be OL but are about 0.35 V (diode value). They are not shorted together. The lines go to somewhere under the hdmi shield which is difficult to remove.

Sorry man, I don’t work on the docks too often so I could be wrong and these line may not even end up here but my best guess would be a fault on the STDP2550 IC, might be worth pulling it apart and checking the other ICs and if they all test good I might start with that one