Lenovo legion 5-15ach6h IT8227E-192 CXA shorted, repaired but no screen / no boot

[pappothar]

i'm not familiar with these testing, i've never own a scope, but it's quite obvious the test is ok, not the result, try pressing down the cpu and retest

I pressed, no change, the 32khz oscillator is still OL with multimeter

[pappothar]

[QUOTE=DeXXter;n3740126]

I found this video vith the oscillator issue, but the multimeter is connected with positive to GND ! in this case i measure the diode voltages, but is it right ?
https://www.youtube.com/watch?v=4lBdUQ3gkd4

[Davi.p]

try to boot detaching the screen, if the cpu has control to the display feed then probably display has a fault, check also resistance between disp..vdd and gnd, if is open probably the input fuse is open, if shorted or low ohm then bad tcon board

[pappothar]

try to boot detaching the screen, if the cpu has control to the display feed then probably display has a fault, check also resistance between disp..vdd and gnd, if is open probably the input fuse is open, if shorted or low ohm then bad tcon board

ALready done, the LCD is unconnected now, the display fuse is ok, is not open. The led_vdd voltage si present on the display connector (20V), but +LCD_VDD is strange, when i switch on the notebook it goes up and down and then stays off, with or without the panel connected (see picture)

[Davi.p]

Laptop lcd panel are i guess fed by 5v, can you trace the lcd vdd step down output if it has problems? Injjecting voltage you can spot bad caps etc..

[DeXXter]

[QUOTE=pappothar;n3742309]

I found this video vith the oscillator issue, but the multimeter is connected with positive to GND ! in this case i measure the diode voltages, but is it right ?
https://www.youtube.com/watch?v=4lBdUQ3gkd4

Weird that you get oscillation...
In any case to measure on diode mode you need the laptop tured off, not connected to battery nor adapter, with the positive probe on ground and with negative one on the rail you want to measure.
Usually on 32khz you should get around 750-800 mV. If you get an OL on one of the sides then you most probably got a soldering issue under the cpu. Usually to repair this you have to desolder, reball and resolder the cpu.

[pappothar]

[QUOTE=DeXXter;n3742346]

Weird that you get oscillation...
In any case to measure on diode mode you need the laptop tured off, not connected to battery nor adapter, with the positive probe on ground and with negative one on the rail you want to measure.
Usually on 32khz you should get around 750-800 mV. If you get an OL on one of the sides then you most probably got a soldering issue under the cpu. Usually to repair this you have to desolder, reball and resolder the cpu.

ok thanks, with the probe with + on gnd, i got diodes on both cristals, so it does not seem to be a ball crack problem, also the diodes are ok if i press or heat the cpu, so it seems ok after all
The weird thing is that i got only KB backlight and fans, the display is off, the +lcd_vdd is pulsed and i tracked back the signal until the cpu, the signal CPU_ENVDD is pulsed exactly in the same way, 3 pulses always the same on - off time, so cannot be a coincidence... DAMN !

[pappothar]

Laptop lcd panel are i guess fed by 5v, can you trace the lcd vdd step down output if it has problems? Injjecting voltage you can spot bad caps etc..

but the display is disconnected, it cannot be a short on that side of the connector

[Davi.p]

no, i mean, is the the display fed by a 5v? If yes its dc dc is on the main board..

[pappothar]

no, i mean, is the the display fed by a 5v? If yes its dc dc is on the main board..

no, its fed by a 20V and a 3.3V, the 20v is steady, the 3.3 is pulsed as shown in the oscillogram above

[Davi.p]

ok so the 20v does not matter is for backlight, the 3,3v is for lcd, so check the 3,3v lcd vdd supply directly on the coil if is steady

[pappothar]

yes it is perfectly steady