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820-3330 Green Light, No Power

S

SMMRepair

Member
Working on an 820-3330 board that has green light, but no power. No liquid involved. Using genuine 85W charger.

- All main rails present (5v_s5, 3v3_s5, ppbus, 3v42)
- Nothing gets warm, no shorts detected.
- PPVRTC_G3H present
- PM_DSW_PWRGD present
- PM_SLP_SUS_L present, but PP5v_SUS and PP3v3_SUS both missing.

- Q7820: my gate (pin 3) is 3.3v, and my source (pin 4) is 3.34v, but my drain (pin 1) is 0v.
- Q7840: my gate (pin 3) is 4.92v, and my source (pin 4) is 5.02v, but my drain (pin 1) is 0v.

Are these two MOSFETs bad? My gate is lower than the source on both, but the drain on each is 0v. If I'm on the wrong track, please just let me know. Since I've got PM_SLP_SUS_L, but not PM_SLP_S5_L, and I'm missing 5v_sus/3v3_sus, I'd assume this is where my issue is.

Any help appreciated!
 
Last edited:
TCRScircuit

TCRScircuit

Super Moderator
Staff member
Sorry SMMRepair Was half asleep and didn't drink any coffee yet when I made that comment. It is very possible that those fets are bad.. However, Something killed them. Bad controller most likely and the controller most likely took out all the fets in that circuit as well. Replace the TPS51980 and replace the FETs in that circuit and see if it fixes it.
 
Gurmon

Gurmon

Member
yes its true, however since OP has 3v3_s5, U7201 probably isn't an issue just yet.

Since PM_SLP_SUS_L is present, have you checked if this translates into P5VSUS_EN ? If not whats SMC_BATLOW_L ?
 
D

dukefawks

Administrator
BATLOW_L is probably not present. Does this board charge a battery? Does it power on from a charged battery?
 
S

SMMRepair

Member
Hey Duke, the board does not power from a charged battery, and it does not charge the battery. SMC_BATLOW_L is missing, yes.
 
S

SMMRepair

Member
OK, so I have an update: I replaced the SMC, and I now have pp3v3_sus and pp5v_sus, as well as SMC_BATLOW_L (3.3v). I still have no fan spin, but my PCH does get warm (not hot), so I think I'm now missing another s0 rail (or my PCH is bad), but I'll do some more digging and update the thread in a bit.
 
S

SMMRepair

Member
OK, I'm stuck at a point again. Not having a proper block-diagram with progressions/orders of rails makes it very tough. I have 3v3_sus and 5v_sus, but no PM_SLP_S5_L. I'm either missing something after 3v3/5v_sus but before pm_slp_s5_l, or my PCH is bad. The PCH gets slightly warm when the board is powered, which makes me think it's getting told to turn on, but nothing after that. I'm not sure how to confirm this, however. Any ideas on what I should check next? Thanks again.
 
S

SMMRepair

Member
OK, thanks, duke! Identifying a failed PCH is just as helpful in learning as fixing the board. I'll send this one off to my more-skilled partner to get the PCH replaced. Thanks, Duke!
 
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