Asus Taichi31 NO POST - schematics inc.

[Formaster]

Hey Guys,

A Taichi31 not posting. Power led lit, cpu/gpu getting warm, both screens/hdmi blank.

Power rails checked, all Voltages found correct, except two. First is a VGFX Core, which i think the secondary power for the cpu, maybe right is off.

The second is a mosfet gate, which not give a 1.5V. First thinked to soldering a 1.5V jumper, but checked a few voltages around and found a mistake.

On a capacitor below measured 6.5V instead 1.5V boot voltage, the other side of the cap is already 1.5V. Just included the schematics too, if somebody can check please.

[mon2]

Re: Asus Taichi31 NO POST - schematics inc.

Try to reflash the BIOS first. Had a similar case in the last 24-48 hours in this forum for another brand of PC with the same issues - no Vcore & no GPU voltage rails = no POST. The issue was resolved by just reflashing the BIOS. Attempt this first.

Reference:

https://www.badcaps.net/forum/showthread.php?t=98548

[Formaster]

Re: Asus Taichi31 NO POST - schematics inc.

Don't know where i did wrong. Click on the IC type in AsProgram than nothing happening. On the VCC is 3.3V right. The device recognized, paralell firmware installed.

[Formaster]

Re: Asus Taichi31 NO POST - schematics inc.

Wrote the newest BIOS to the eeprom, not helped. (The problem was the 5V data lines on ch341a, thats fixed.)

I suspect that 6.5V instead 1.5V boot curcuit. Would anybody have any suggestion as to whether this is normal?

[SMDFlea]

Re: Asus Taichi31 NO POST - schematics inc.

Wrote the newest BIOS to the eeprom, not helped. (The problem was the 5V data lines on ch341a, thats fixed.)

I suspect that 6.5V instead 1.5V boot curcuit. Would anybody have any suggestion as to whether this is normal?

The bios at the support site is 6MB ,did you merge it with your backup .

[Formaster]

Re: Asus Taichi31 NO POST - schematics inc.

of course, must be 8MB the bin. Also checked from badcaps with working one, same results.

Other suspect is the mosfet, on input side there is 1.5V, but gate nothing. Thinking on desolder and jump the 1.5V, but don't want to kill the MB. Means?

[SMDFlea]

Re: Asus Taichi31 NO POST - schematics inc.

of course, must be 8MB the bin. Also checked from badcaps with working one, same results.

Other suspect is the mosfet, on input side there is 1.5V, but gate nothing. Thinking on desolder and jump the 1.5V, but don't want to kill the MB. Means?

Never jumper any mosfets. Post the mosfet part number so we don`t have to look at a picture,post voltages.With no poswer test resistance to ground, and check S/G/D .If you suspect its bad test it out of circuit, desolder it.

[Formaster]

Re: Asus Taichi31 NO POST - schematics inc.

PCY01 FDMC 8884 mosfet type.

Desoldered to check, drain to source under 0.7Ohm, drain to gate 81Ohm. Think is dead.

[SMDFlea]

Re: Asus Taichi31 NO POST - schematics inc.

PCY01 FDMC 8884 mosfet type.

Desoldered to check, drain to source under 0.7Ohm, drain to gate 81Ohm. Think is dead.

measure source to drain

[Formaster]

Re: Asus Taichi31 NO POST - schematics inc.

both direction the same result.

[piernov]

Re: Asus Taichi31 NO POST - schematics inc.

If you had 1.5V on the 1.5V power rail why would the MOSFET be bad?

[Formaster]

Re: Asus Taichi31 NO POST - schematics inc.

On VGFX Core did'nt have the 1.5V