What happens with 5150?

Hello. I've bought an Inspiron 5150 on ebay and i'd good luck because at the first problem it was in warranty and dell had repaired in less that 24h at my home. Now the warranty was elapsed. Some days ago i found that the battery is not charging and when i move the DC plug works fine. One day that trick not was enough. The female DC jack has a lot of backlash and I decided to change it because I'm out of warranty. I replaced the socket without problem and the laptop don't start too. When I was waiting for the spare socket the laptop was working well with batterie untill it was exhausted.
I don't want to spend too much money on this reparation sending to service.... Now I hope the problem could be the AC adaptor or the mainboard... Could be a good deduction?. I've a 0-30V 10Amp adjustable power supply but I can discard the power adaptor because of 'data' communication. There is some procedure to check or to 'bridge' (or jump) the data signal from the adaptor? to discard if it's faulty?
When i power up the laptop I get a flash lights ( power and battery LED) and then 10 blinks on battery LED (without AC adapter). If the laptop is plugged the battery led is on 10 seconds and then stops. The DC voltage (laptop plugged) is 19.33V. In the data cable I can see a 'sawtooth' of 5mv and T=0.6msec..... NOISE!! I've checked data cable continuity from AC adaptor (where the cable is solded) and the mainboard and it's OK....

Some clues will be welcome!

I hope I don't need to change the EXPENSIVE MB
Best regards