DELL 1558, no power up. DAFM9CM

[inflex]

Dell 1558 not powering on.

Battery is charging.
3V3 / 5V fine out of TPS51427, but 15V_ALWP is stuck at 5V as if the charge-pump isn't working.

PD11/12 seem fine. Caps PC187 / 188 / 190 / 191 all seem fine.

I imagine the DL2 drive to the charge pump must be working else I'd not be getting 3V3 off PL9 / PC189 etc.

[JaroTech]

Re: DELL 1558, no power up. DAFM9CM

Hi, follow the power sequence on page 59 of the schematics, check if a voltage is missing.

[inflex]

Re: DELL 1558, no power up. DAFM9CM

That's what I've done, and I'm stuck at +15V_ALWP being pulled down to 5V and I'm not entirely sure what's going on at this point. I pull PQ43 off and it'll come back up, so it seems like there's a load exceeding the compliance of the charge-pump. The PQ43 measures 57K between 1-2 as expected.

Might just go and wipe out the whole charge-pump area and build with new parts just to get that as a "known good area".

[JaroTech]

Re: DELL 1558, no power up. DAFM9CM

How much voltage do you have on the PQ43 collector?

[inflex]

Re: DELL 1558, no power up. DAFM9CM

4.45V on PQ43 collector (and emitter). If I take PQ43 off, it rises back up to 14.5~15V.

Resistance to ground (from PQ43 collector) is about 15MR.

Both PQ43 and 44 have been replaced with the same outcome.

[inflex]

Re: DELL 1558, no power up. DAFM9CM

UPDATE: Seems like it's a charge-pump compliance issue. If I replace PQ43 with a resistor from emitter -> GND, at 25K it's 5.5V, at 50K it's 7.5V.

For what ever reason, the charge pump isn't working as well as it should be.

[inflex]

Re: DELL 1558, no power up. DAFM9CM

Starting to think that maybe the 15V_ALW doesn't actually maintain 15V until it's in a S0, or maybe S3 state.

As it is, i've given up for now. For all I know it's the IO controller playing silly-buggers with me.

[caspian]

Re: DELL 1558, no power up. DAFM9CM

how much voltage is on pin 2 and 3 of PQ44? how much resistance is on pin 3 of PQ43 to GND?