HP Probook 4515s power issue

[bollin]

Hello

I have a Probook 4515s that will not start. When plugging in power adapter nothing happens. No leds light up. On battery the leds on DC jack starts blinking, indicating low battery.

I have investigated it this far:
Q508 source 19.5v, gate 19.1 v d 0v
-> q508 tested ok

U509 pin 7 = 18-19v (can´t remember)
pin 8 = 19.5v
pin5 = 5v

q508 pin 2 = 9v

r573 = 45kohm (with u509 removed)

Unfortunately I couldn´t find any 1M resistors, will check my scrap mobos when I find them.

Since I don´t have much experience I would like to know if you think I am on the right track?

[bollin]

Re: HP Probook 4515s power issue

Btw, the reason why it broke was when the power adapter (18.5v 65w) stopped working. I had another one lying around (19.5v 65w), but then this. It did however show some signs of life the first time I plugged it in.

[BlueMidnight]

Re: HP Probook 4515s power issue

Forget R573. You should read it as roughly 40K. Close enough. This is a good example of why measuring components in circuit can be really misleading. If you place your probes on both sides of R573, there are actually 3 paths connecting them (see attached pic). Once you know all the current paths, you can use the standard series/parallel equations (or an online calculator) to find out what the combined resistance should be.

Q508 is turned off. It should be on. It's off because the gate is high (I'm assuming that Q508 is good because you said it tested ok). You need to find out why the gate is high.

I would start by measuring all the pins of Q511 and D507.

Under normal circumstances, Q511 should be turned on and ADP_EN# should be connected to ground. That causes R557 and R48 to act as a resistor divider and set the gate of Q508 to roughly 6V.

If the gate of Q508 is not 6V, then the only other valid state is to be equal to +VADP (19.5V in this case). But it's not. It's a little bit less (19.1V). This could be a hint as to what is going on. Basically, it is acting as though R48 has a value of 2K instead of 220K. It's rare for a resistor to fail shorted though. A short between the source and gate of Q508 is much more likely, but I am again assuming you've tested that correctly (i.e. you checked for a short between source and gate by using a multimeter in diode mode and measuring with the leads in both orientations). Another likely possibility is a short through C44.

But again, start by measuring Q511 and D507.


Edit: I should clarify that there are actually more than just the 3 paths in the pic. Those are just the ones in that one area of that one page. Though some paths are such a comparatively high resistance that they can be ignored.

[bollin]

Re: HP Probook 4515s power issue

Ok, thanks for the reply. If I remember correctly all pins on q511 read between 19.5v and 18.8v.
I will try check these when I can find the time. However, the signs are pointing at a faulty q511, right? If It was working I would have 0v on source? If d507 were to be the culprit it stilll wouldn´t explain the voltage found on u509, is this correct?

[BlueMidnight]

Re: HP Probook 4515s power issue

At this point, I don't think Q511 is the culprit. But that could change. Let's just start with measuring some voltages on Q511 and D507 and then go from there. Oh and I would add U509 to that list also. I know you had a few of the pins listed, but I'm curious about pin 6. Might as well measure all 8 while you're there.

[katfish]

Re: HP Probook 4515s power issue

Btw, the reason why it broke was when the power adapter (18.5v 65w) stopped working. I had another one lying around (19.5v 65w), but then this. It did however show some signs of life the first time I plugged it in.

Just curious ... that 19.5v wasn't a dell adapter was it?

[bollin]

Re: HP Probook 4515s power issue

No, it was a HP one. Strangely they have two different 65w versions that look exactly the same, but one is 18.5v and the other is 19.5v

[bollin]

Re: HP Probook 4515s power issue

tried replacing q511, no big change but now the led blinks once when i measure volts.
q511 voltages:
1 (gate): 19.15 volts
2 (source): 18.2 volts
3 (drain): 19.14 volts

d507:
1: 18.6 volts
2: 17.8 volts

U509:
1: 0v
2: 5.9v
3: 0.17v
4: 0v
5: 5v
6: 0.17v
7: 18.6v
8: 19.35v

This time I used a adapter that is 18.5v, so +VADP=19.35v

[bollin]

Re: HP Probook 4515s power issue

Problem solved!
Thanks to BlueMidnight, I followed the path of LimitSignal, and discovered that a pin in cn502 was bent. Straightened it up and it powered up nicely. Only problem now is that bios is corrupted, so I need to flash it. I believe I have a copy somewhere.

[BlueMidnight]

Re: HP Probook 4515s power issue

Great news! Yes, pin 6 being less than pin 5 is a problem. Hope the rest goes smoothly.