No power Lenovo Yoga 920-13ikb (DYG60 NM B291 Rev 1)

[FastFreddi]

Hello, I have a Lenovo Yoga 920-13ikb (DYG60 NM B291 Rev 1) which will no longer power on. Charge light does not come on when I plug in the adapter. I have the schematics but could use a little guidance as to which measurements to take to troubleshoot the board. With the battery and USB-c power connected, I get 20v at PQ8, 6.18v at PQ10. Let me know if you require further info to assist me. Also if it makes a difference, approximately a week before the inability to power on, my keyboard and trackpad was going unresponsive. Disconnecting then reconnecting the battery appeared to have resolved that issue, but I suspect this was the start of the hardware failure.

[FastFreddi]

Re: No power Lenovo Yoga 920-13ikb (DYG60 NM B291 Rev 1)

I'm new at this. But is VIN the main power rail to the board? What kind of voltage should I expect on PQ9? Looks like PQ12 goes to the battery?

[mon2]

Re: No power Lenovo Yoga 920-13ikb (DYG60 NM B291 Rev 1)

Hi fellow Canadian.

Yes. VIN is the power input from your adapter. The voltage is variable and you have power delivery support. This design features the Cypress power delivery controller. The logic board and external adapter chat with each other using the CCx lines on the usb interface.

After a positive packet exchange, the CG4 (cypress) controller requests 20v to power the logic board. You have this and is a good start.

Suggest to power down, no battery. Meter in resistance mode (200 ohms is ok).

Then check the resistance to ground of every large inductor on the logic board. This testing may reveal a bad cap that is causing the rail to shut off due to a short circuit of a part like a stale capacitor.

Post the resistance values that are super low like under 10 ohms to ground. Use the 200 ohm setting of your meter. If you find a low value, post the the inductor label so we can check against the schematic.

It is also possible that one of your mosfets is bad. We can check them after this test.

[FastFreddi]

Re: No power Lenovo Yoga 920-13ikb (DYG60 NM B291 Rev 1)

Ok so impedance at the inductor revealed PL7 = 25, PL13 =12.9, PL14 = 6.9 and PL15 6.8. PL8 and PL6 transiently read 20-170 then no conduction to ground. Not sure if that helps. Thanks for your assistance.

[FastFreddi]

Re: No power Lenovo Yoga 920-13ikb (DYG60 NM B291 Rev 1)

I'm not entirely sure how to test the mosfets but PQ8 with my multimeter in diode mode reads about 0.49 volts in one direction, then transiently 2.5 volts in the other direction, then OL. All the others seem to read around 0.49 one way but stay around 2.5-2.6 the other way. I was expecting OL the other way for all, this behaviour persists despite shorting the gate to the source pins.

[mon2]

Re: No power Lenovo Yoga 920-13ikb (DYG60 NM B291 Rev 1)

Can you post your schematic for this unit? Unable to find it in my database. Found the NM-B921 but not NM-B291.

[FastFreddi]

Re: No power Lenovo Yoga 920-13ikb (DYG60 NM B291 Rev 1)

Here is the diagram

https://www.badcaps.net/forum/showthread.php?t=76237

.

[mon2]

Re: No power Lenovo Yoga 920-13ikb (DYG60 NM B291 Rev 1)

Let us check the mosfets.

Reference material:

http://electronicsbeliever.com/how-t...-is-defective/

The table on the above webpage is quite useful.


1) Remove all power (no adapter & no battery).
2) Meter in resistance mode (200 ohms is ok).
3) For each mosfet, check & post the resistance between:

a) source (1-2-3) & drain (5-6-7-8)
b) source (1-2-3) & gate (4)
c) gate (4) & drain (5-6-7-8)

NB: You can select any of the pins that are shorted together (ie. 1-2-3 = any one will do as they are shorted together on the PCB).

Measure the resistance on each of the mosfets and post their values for:

PQ8, PQ9, PQ10, PQ11.

[FastFreddi]

Re: No power Lenovo Yoga 920-13ikb (DYG60 NM B291 Rev 1)

That link is useful thanks.

PQ8 S-D OL S-G 192 G-D OL
PQ9 S-D OL S-G 180 G-D OL
PQ10 S-D OL S-G 193 G-D OL
PQ11 S-D OL S-G 181 G-D OL

[mon2]

Re: No power Lenovo Yoga 920-13ikb (DYG60 NM B291 Rev 1)

These mosfets look ok. OL means that the resistance is so high that it exceeds the meter setting used during these tests. That is a good sign. Even the hundreds of ohms readings is ok and is not considered a short circuit.

Proceed to do the same testing of the battery mosfet @ PQ12 and post their values.

Again, do so with no power to the logic board.

[FastFreddi]

Re: No power Lenovo Yoga 920-13ikb (DYG60 NM B291 Rev 1)

Ok the pins are tiny on this one so to be sure I had contact, measurements were done off PR53, pin 22 and 21 on PU9. All measurements for PQ12 are OL.

[mon2]

Re: No power Lenovo Yoga 920-13ikb (DYG60 NM B291 Rev 1)

Ok. That is a good sign.

At this stage, recommend to measure and post each voltage reading of the charger IC.

Meter in DC volts mode and select a voltage setting that is 30V or higher to allow for all readings to be measured.

Black meter lead to ground (metal shield is ok) & RED lead to the pin to be measured on this IC.

Be patient and take your time as the pins on this QFN (square) device are small. If necessary, you could measure the voltage at other parts that are nearby but note this when you are posting. We just do not want any slip of the probe to cause any other faults / damage.

Locate the pin #1 on the device by finding the dimple (indentation) of the topside. That corner will have the pin #1 and then go counter-clockwise for the pin order from there. See attached.

[s_henya]

Re: No power Lenovo Yoga 920-13ikb (DYG60 NM B291 Rev 1)

did you eventually fix this MB?