Main rail / charging circuit issues on Bucky/BenSolo 17859-1 board from Dell Vostro 5581

[benwaterson]

Hi All

Been a while since I have been here, and a bit rusty.

I have the above laptop motherboard that was working and now the charging circuit is faulty.

Have 19v in fine until it hits PU4403 - not shorts I can see and thermal cam reveals nothing.

I have swapped out the ISL9538 and also the two mosfets (PU4403 and PU4405). Have 2.8v at the power switch, which pulls low when pressed - charging light comes on and goes straight off

Below are measurements (pin names are per the datasheet for the ISL95338 (couldn't find one for ISL9538, but believe they are the same) - https://www.renesas.com/us/en/docume...5338-datasheet

Without Battery, With Charger

1 - CSON = rises to 2.3v
2 - CSOP = 2.3v
3 - VOUTS = 2.3v
4 - BOOT2 = 5v
5 - UGATE2 = 0.74v
6- PHASE2 = 0.74v
7 - LGATE2 = 0v
8 - VDDP = 5.2v
9 - LGATE1 = 0v
10 - PHASE1 = 0.74v
11 - UGATE1 = 0.74v
12 - BOOT1 = 4.9v
13 - ADPS = 18.4v
14 - CSIN = 18.8v
15 - CSIP = 18.8v
31 - VOUT = 2.3v

With Battery, With Charger

1 - CSON = 11.8v
2 - CSOP = 11.8v
3 - VOUTS = 11.8v
4 - BOOT2 = 5v
5 - UGATE2 = 2.76v
6- PHASE2 = 2.76v
7 - LGATE2 = 0v
8 - VDDP = 5.2v
9 - LGATE1 = 0v
10 - PHASE1 = 2.76v
11 - UGATE1 = 2.76v
12 - BOOT1 = 4.9v
13 - ADPS = 18.4v
14 - CSIN = 18.8v
15 - CSIP = 18.8v
31 - VOUT = 11.8v
32 - BGATE = 3.3v

When powered, pins 10 and 11 show 1.2ohms (and voltage is same on both). Removed MOSFET and low resistance remains - measured the next morning and resistance is in the megaohms range?

Gate is opening for PU4412 when battery is connected, hence the 11.8v at VOUT.

I have more ISL Chips / MOSFETS on order from aliexpress, so can change out the lot when they arrive.

Also, PROCHOT appeared to be pulling low.

Any insight as to what may be going on?

Cheers

[mon2]

No power during resistance or diode measurements.

Meter in dc volts mode (30 v or higher).

Measure the voltage to ground of ACOK pin with only the power adapter. This voltage should a logic ‘1' or ~3v3 if the power adapter is considered to be ok.

[SMDFlea]

LINK to schematic - https://www.badcaps.net/forum/troubl...-tvmhg-17859-1

[benwaterson]

No power during resistance or diode measurements.

Meter in dc volts mode (30 v or higher).

Measure the voltage to ground of ACOK pin with only the power adapter. This voltage should a logic ‘1' or ~3v3 if the power adapter is considered to be ok.

The adaptor is fully functional (if that is what you are asking?) - just tried on another Dell and charging as expected.

I have pulled the 2 mosfets 4404/4405 temporarily to test them out of circuit - they seems fine (I can replace them to test as you described though)

One thing to also not, if just battery connected then I still see the same behaviour with the charging light / no main rail power..

[benwaterson]

LINK to schematic - https://www.badcaps.net/forum/troubl...-tvmhg-17859-1

Thanks, sorry should have linked to that.

[benwaterson]

Ok, well this is interesting - resoldered the mosfets, plugged in the AC adaptor and now the charging light is on and getting 12.56v on DCBATOUT!

Makes me wonder if one of the mosfets was soldered in backwards!

Will run some more tests and see if it now powers up.... will report back - would pulling the CMOS battery and reattaching reset some kind of failure mode flag (had the CMOS battery connected before now)

[benwaterson]

So no further progress so far.

Just on battery it just has the light on once then off behaviour, solid light with AC.

With AC and battery getting these voltages now - is 4.6v reasonable or way too low? (was 2.76v before).

[benwaterson]

No power during resistance or diode measurements.

Meter in dc volts mode (30 v or higher).

Measure the voltage to ground of ACOK pin with only the power adapter. This voltage should a logic ‘1' or ~3v3 if the power adapter is considered to be ok.

ACOK is 3.3v as expected also

[mon2]

Post the voltage to ground measurements of the attached regions of your board.

[benwaterson]

1) 115k (at test point just above unpopulated/soldermasked r4317)
2) 2.25k (at r4305)

[mon2]

Attach the power adapter and measure the voltage at the above points (not resistance).

[benwaterson]

1) 156mv
2) 158mv

(sorry misread the question and measured resistance to start with)

[benwaterson]

Also to note these 3 things:

1) If plugging in the AC adaptor (after boards caps have discharged) - the charging light flickers rapidly for 2 or 3 seconds and then goes solid white
2) There is noticeable coil hum from PL4501 (3.3v)
3) The 3.3v voltage here is 0.85v

[mon2]

The voltage to ground measurements for the PS_ID are not correct. This can also lead to the observed issues.

Remove all power. Meter now in resistance mode. Measure the resistance to ground on each side of this same PS_ID line. We are checking if the diodes @ D4303 are shorted or not.

The PS_ID interface and fix is well documented on this website but in short, is a single wire (Maxim / Dallas Semiconductor) communication line with the external power adapter. This single wire must operate correctly and is read by the EC (8051 microcontroller based) to gauge if the power adapter is worthy enough to power the logic board and charge the battery. Absence of this communication and the logic board will shut off.

Moving forward, you can remove D4303 off the board and confirm if the PS_ID line on the power adapter side returns to ~3v3. If yes, then the line should be ok to test again. If not, remove the mosfet @ Q4301. After this removal, confirm the voltage on the RIGHT side of the schematic which is the EC side. This line must offer a ~3v3 measurement in parked mode.

These ~3v3 values are used to power the single wire ID IC that is implanted inside of a true Dell power adapter.

[benwaterson]

Ok, thanks for the detailed explanation.

Measuring D4303 resistance :

Pin 2 negative / Pin 3 positive - 115k
Pin 1 negative / Pin 3 positive - 115k

Pin 2 positive / Pin 3 negative - 115k
Pin 1 positive / Pin 3 negative - 115k

i.e its just measuring R4302 / R4309 path to GND

Diode mode measures it correctly I believe - 0.685v voltage drop or OL the other way around - so doesn't look shorted on either diode.



Are the resistance measurements i (accidently) gave before the ones you need?

"1) 115k (at test point just above unpopulated/soldermasked r4317)
2) 2.25k (at r4305)"

I can remove the diode to test quickly without it.

[mon2]

The resistance looks to be ok.

Confirm the voltage to ground of the following (still in this area of the PS_ID circuits):

R4304, pin 1 = 3D3V_S5
R4303, pin 1 = 5V_S5 (used by mosfet Q4301)

[benwaterson]

Diode removed, still 156mv

[mon2]

See post #16. If the required pull-up voltages are present and you still see a low voltage on the PS_ID signal line then the EC controller is a suspect. Internal to this EC is a 8051 microcontroller that is 'bit banging' to the 1-wire protocol to communicate with the power adapter. This communication must proceed else the logic board will not know the power rating of the adapter.

[benwaterson]

The resistance looks to be ok.

Confirm the voltage to ground of the following (still in this area of the PS_ID circuits):

R4304, pin 1 = 3D3V_S5
R4303, pin 1 = 5V_S5 (used by mosfet Q4301)

3D3V_S5 = 0.845v
5V_S5 = 4.95v

So does seem to be a partial short on 3.3v?

[mon2]

Remove all power. Meter in resistance mode. Measure the resistance (not diode mode) to ground of 3D3V_S5.