La-7912p

[ziko07]

Hi, I have 2 same bords for repair
-On first one I founded shorted first fet and a shorted CAP to mail rail. I tought will be ok but there is missing +VGFX_CORE voltage. Same controler for +VGFX_CORE and +CPU_CORE
+CPU_CORE is present on both phases. I found 15 Ohms on UGATE1G on controler that drive highside fet (on other board this pin is in kohms)
Can be only this part of controler shorted internally?

-second power led ok when press button VR_ON present but no +CPU_CORE

First board take 28mA,what I think its much second board only 8mA,before pwrbtn pressed

Any tips?
See images, one for first other for second board

[mon2]

Re: La-7912p

Start with the voltage to ground of B+ main rail with the official and recommended power adapter.

What is the measurement?

[ziko07]

Re: La-7912p

its, 19.2v (not have ori adapter) I use labaratory bench power
Speak for second board, but firs also has 19v powe rail OK

[Techtiger]

Re: La-7912p

is the Run Power sector work fine VS ? Link the schematic in the Schematic section

[ziko07]

Re: La-7912p

UPDATE:
-first board had shorted first fet and shorted CAO on main rail (repl and and laptop start but no voltage on +VGFX_CORE coil

-second ahd power but no VCC_core, and I saw no +5VS on CPU controler pin, actually +5vs was missingfrom +5valw to +vs, and found open 20k resistor (see image)

Summary, now both boards has all power except voltage on +VGFX_CORE coil
I not have LCD and testing on external HDMI but no have picture of course

Now any other ingo about +VGFX_CORE

Tnx

[ziko07]

Re: La-7912p

There is PGOOD and PGOODG
First is enable for CPU_CORE, second is for +VGFX_CORE
As you can see from image on working cpu_core on both sides or resistor there is 3v3
On not working PGOODG is 3v3 form one side of resistor only

Resistance +VGFX_CORE to GND is 16 Ohms
When board are powered take 650mA and I can see PCH getting hot and not have heat sink on it

Also I put usb keyboard and no any light on keyboard, with both boards.
5v is present on usb port

[ziko07]

Re: La-7912p

I apologise for too many posts but I do car electronics, this is new for me.
So,one board has shorted main rail, I fixed
Second led comes ON but missed CPU_CORE voltage, I found open resistor because +5VS was missing, I fixed that too.
Now....both boards fixed (were different problems) and both have no vgfx_core, so my final question is: is it possible because no screen connected? Because I doubt both boards now to have same problem after fixing other problems on them

P.S. please see also above post, about no 3v3 on pgoodg line

[mcplslg123]

Re: La-7912p

This board doesnt require screen to be connected for post,so this cant be the reason for missing GFX core. Try replacing ISL95836,replacing the CPU and flashing a known good Main bios+EC.

[mcplslg123]

Re: La-7912p

If you have oscilloscope, Measure Upper gate and lower gate of Fets on VGFX rail. you can expect 20-24V on UG and 5V on LG(Just a rough idea and may differ from board to board).

[Sephir0th]

Re: La-7912p

I have the feeling in this thread +VGFX_CORE was confused with +VGA_CORE multiple times. The behaviour was discussed many times before. +VGFX_CORE is not a requirement to perform the P.O.S.T since it only shows up under load, like when loading the OS for example.

[ziko07]

Re: La-7912p

I have the feeling in this thread +VGFX_CORE was confused with +VGA_CORE multiple times. The behaviour was discussed many times before. +VGFX_CORE is not a requirement to perform the P.O.S.T since it only shows up under load, like when loading the OS for example.

I will search for screen to test that's I asked becouse can't be 2 boards same problem after repair other problems
Tnx

[ziko07]

Re: La-7912p

Tried with screen,hdd,hdmi and not work, no image
Also when insert usb keyboard caps lock is not light
On DIMM_DRAMRST# has 1.5v, shouldn't be half voltage 0.75v ?

[ziko07]

Re: La-7912p

I saw on YouTube when missing gfx they put external buck convertor. Can I try,what voltage exactly need?

Tnx

[mcplslg123]

Re: La-7912p

I have the feeling in this thread +VGFX_CORE was confused with +VGA_CORE multiple times. The behaviour was discussed many times before. +VGFX_CORE is not a requirement to perform the P.O.S.T since it only shows up under load, like when loading the OS for example.

Agree but only partially. On older boards with 1st-3rd gen socket type cpu,+VGFX Core is a must for posting and it appears as soon you trigger the Motherboard. Eg, Sony MBX-269.

[mcplslg123]

Re: La-7912p

I saw on YouTube when missing gfx they put external buck convertor. Can I try,what voltage exactly need?

Tnx

You can remove the +VGFX Coil and inject voltage on the consumer side. Should start with 0.5V and may gradually go up to maximum 0.9V. ANything higher will kill the cpu. Usually on older boards i inject 0.5-0.9V with my dc supply for test purpose.

[ziko07]

Re: La-7912p

update: I get other ddr3 memory. put and finaly 0.45v on gfx and picture comes
now boart takes 08-0.9A before 0.65A

second board with new ram, it comes and goes off twice, in that time cpu core present and lost, "without ram memory cpu_core is present"
VR_ON signal is present
Any sugestion?

both board has same flash in both flash memory
now will play with second board

Tnx to all