820-2936-B Rails pulse (except PP3V42 and PPBUS)

[djdblaster]

Water damage. Cleaned with UC. Checked pins 17/18 and 27/28 at ISL. Changed few resistors and ISL. Fixed Q5300 missing 2 pads and made jumpers for pins 3 and 4.

PP3V42 --- 3.47V
PPBUS ---- 12.59V
PP5V_S5 pulses
PP3V3_S5 pulses
PM_BATLOW_L pulses
SMC_ADAPTER_EN pulses

What could I be missing?

 

[JohnB8812]

Does CPU VCore pulse?

 

[djdblaster]

No.
PP3V3_S3 --- 0.1-0.3V pulses
PP5V_S3 ---- 0V

 

[JohnB8812]

Ok check all rails for shorts? Very common for PP5v_S3 to short near the Audio Chip.

 

[djdblaster]

You're right. I get almost full short on PP5V_S3. Time to look where it pops out. Thanks John!

 

[JohnB8812]

You're welcome! Let us know if that fixes the issue.

 

[djdblaster]

I found U4800 heating. Removed it and PP5V_S3 bumped to 0.105V diode mode. Schematics says Critical Omit. Can I start board without it or first replace/check/etc?

 

[JohnB8812]

If that relieved the short, you will be fine without it. It's for the IR controller which is not used by literally anyone. Make sure the short is gone, and if so, see if it starts.

 

[djdblaster]

Okay, just plugged in charger. Nothing. It shows on DMM 0.004V diode mode and slowly goes to 0.105V. But no voltage when I connect charger.

 

[JohnB8812]

I'm guessing the short is still there then check resistance mode what is your resistance to ground on PP5v_S3?

 

[djdblaster]

After unplugging charger, shows 10 Ohms then goes to more than 6 kOhms. As soon as charger connected, resistance drops to very low like 10 Ohms.

 

[JohnB8812]

Do not measure resistance with power applied!!!!! Good way to destroy your multimeter. If it is 6kohms with no power applied, then the short should be gone. You didn't inject voltage with the charger plugged in did you???

 

[djdblaster]

I just wanted to edit post above to say clearly that resistance is not measured with power applied.

I didn't inject voltage with charger plugged in.

So, charger connected, board doesn't start. I unplug it, check resistance (10 Ohms and goes slowly to 6 kOhms). Okay, should be good, thinking to myself. Connect charger again, nothing. Unplug it, check resistance, same thing. 10 Ohms to 6 kOhms.

Edit: so whatever gets power on that rail when charger is connected is obviously pulling down whole rail since it gets hot I think. While not hot, it acts "normal"?

 

[JohnB8812]

Hmm ok gotcha. Sounds to me like there is still some kind of short on PP5v_S3. Inject voltage and see if there is any current draw.

 

[djdblaster]

I've injected 1V, nothing. Probably should go more?

 

[JohnB8812]

Yes for sure. Inject 5 volts and see if any amperage draw. If nothing, then my guess is either U4800 is needed for boot, or there is another issue on the board somewhere.

 

[2informaticos]

There is no short at all.
Allow 10-20s after power removed, before measure continuity on the board.
Any pulse at 5V_S3 now?

 

[djdblaster]

I don't understand. I measured diode mode 20 seconds after power was removed and DMM shows 0.110V.

There is no voltage on 5V_S3. Barely goes from 0V to 0.02 and back. 3V3_S3 cycles though.

 

[2informaticos]

0.110 is not low value at all.
Don't write the end "v" when you post diode mode value; can generate confusion with voltage measurment.
We know what diode reading means.

Remove Q7221 and check again all the voltages which pulse before.

 

[djdblaster]

Q7221 removed.
PP3V42, PPBUS, PP5V_S5 present.
SMC_ADAPTER_EN 0V
PM_BATLOW_L 0V