PPBUS_G3H Shorted to ground with coil put on

ytesfay80

Member
I have this 820-3437 Board that had liquid damage around the 3v42 area and some other areas around the cpu by the fan connector.
I replaced all the components in those areas and I get a light on the charger now but for some reason PPBUS_G3H was only around 3v. I ended up realizing that g3h was shorted to ground in diode mode and when I removed L7130 the short was only on Pin 2 side so I tracked it down to a couple of capacitors that were next to the cpu. I put the coil on and still no change in voltage on ppbus g3h. I checked again and saw that L7130 was shorted to ground and when I removed it the short was gone for some reason.
I put two more L7130s from donor boards and each time I put them on the short appears.

This is something I haven't seen before so do you know what else could be causing this. I already replaced F7140 and that measures fine.
 

smiba

New member
What do you mean shorted to ground?

With L7130 removed, is the short on Pin 1 or Pin 2 on the board?
Resistance to ground in Ohms?
 

ytesfay80

Member
In diode mode with L7130 on the board I am getting 0.004 to ground. With it removed the diode mode readings are normal. Before tracking down and fixing the short previously I was getting 0v to ground on Pin 2 of L7130.
Now its normal and the short only appears when I put L7130 on the board.
I will have to check the resistance in the morning.
 

ytesfay80

Member
Okay I checked again this morning and there was no short. I'm thinking all the heat on the board was messing up my measurements.

Anyways, now I get 8.59v on ppbus but I am not getting voltages on other rails.
PP5v_s5 pulses initially at 5v then just stays at 1.71v. I have 0v and no pulses on PM_SLP_S4_L and PP3v3_s5. There are discolered probe points around the bios chip and u1900 but the components all look good.

Also, I replaced the ISL6259 and the current sense resistors yesterday.
 

dukefawks

Administrator
It was not heat, it is residual charge in the capacitors....

Check the usual corrosion points, U1900, U1950 first. CPU Vcore also pulsing?
 

ytesfay80

Member
No pulse on ALL_SYS_PWRGD.
PP5v_S5 isn't pulsing at 5v anymore and instead it just shows a steady 1.7v.

PPVRTC_G3H is 3.3v
 

ytesfay80

Member
Yes PP5v_S5 is the one thats 1.7v
I cleaned the board a few days ago but I don't believe there was corrosion around the u7501 chip and all the probe points look pretty good around it.

U7501 voltages
Pin 4: 0v
Pin 12: 3.43v
Pin 21: 3.43v
Pin 23: 8.59v
 

ytesfay80

Member
Resistance to ground on 5v_s5 is around 1.7MegaOhms. Diode Mode shows 0.44v
Trace is good on Pin 23 of U7501.
3.31v on Pin 22 of U7501
I did feel u7501 getting slightly warm so I replaced it and still I get the same measurements as before.
 

dukefawks

Administrator
Only thing U7501 needs to generate 5V_S5 is VIN to pin23 and enable to pin 12.
Inject 5V on 5V_S5 and see what current draw it has. Also feel if anything connected to 5V_S5 heats up.
 

ytesfay80

Member
Okay I injected 5v and I got 1.09amp draw and u7501 got very hot again.
Do you think it is the chip again or something else causing it do that? The end of the capacitor on C7505 came off after I took the wire off of it after injecting voltage so I'm going to need to replace that as well.
 

ytesfay80

Member
I replaced u7501 and C7505 and still I only get 1.72v on Pin 1 of C7505. I am getting 8.58v on Pin 23 and 3.42v on pin 12 of u7501.
 

ytesfay80

Member
No it is not getting hot when I had the charger plugged in.
When I removed charger and injected voltage on Pin 1 of C7505, U7501 got really hot at 5v and even around 3v.
 
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