Lenovo Yoga 13 Panasonic, no video, fan OK, missing voltage rail (?)

[jaroslav.psenicka]

Hi all,

I have a Lenovo Yoga 13 Panasonic here, when powered

• both fans spins (the sconds starts with a bit of a delay), no image neither on HDMI nor the display
• most voltage rails seem OK (see image below, red labels)
• resistnace to ground mostly seem OK as well (blue labels)

the only suspicious is the 0.0V rail (2nd from left, top row)

• the resistance to ground is rather low (1.9ohm)
• when injecting the voltage (1V), it consumes around 200mA, seems OK to me (?)

also tried new BIOS, no change
I can't find a schematics for the board - can some of you gurus look at the voltages? are they OK from your POV?

thank you very much,

-jp

[mon2]

See attached. Start with the DCin power connector. The voltage here should match the power adapter voltage. Then review the 2 * DCin mosfets (Q16 & Q17) next. Need to check the voltage to ground of each of these mosfets in the power path.

Post each measurement.

[jaroslav.psenicka]

Thank you very much @mon2,

here are the measurements:



I'm testing the board outside of the laptop, with no battery connected, this may explain the low voltage on the BAT line (?)
the resistance to ground on BAT is almost 500 ohm, looks OK to me
the VIN is 20.1V, sounds good to me either

-jp

[mon2]

These are good measurements to me. Need to check if I have a board view file to check on the referenced 0 volts on the board.

What is the history of the board?

[jaroslav.psenicka]

that would be awesome @mon2,

if I can identify the rail, I may find the mosfet and the corresponding controller, one of these may be bad IMO
I wonder what rail is missing... could be something like B+?
the board is not labeled (no silkscreen), the coil of missing rail is R47 (0.47uH?)

this is actually an ebay find, not a clear history, not many signs of misuse of water damage

-jp