Electronics > Repair
Mainboard with No Picture
<< < (6/8) > >>
GGMM:
2x,

I watched this video.


Without claiming that there is a solution to the problem, it indicates an interesting site, where you can find motherboard schematics.
https://discord.gg/vam6YC8vwU
There are not all models, but it can help
cdt
2X:
First, I tried to turn on the motherboard without CPU. I cut the VID0 trace (before the via) and I connected to GND, so VID4-VID0-VID12.5 combination was “111101” -> Vcore=1.1V (according to table of the page 14).
The result was that now I had the correct voltage on the REF pin (1.1V) but still no PWM pulses on pins PWM1, PWM2, PWM3 (I measured all the voltages on the ISL6565 pins (image 1).

Second, I recreate a PWM signal exactly that I saw on the good one mainboard on the PWM3 pin of ISL6565. Then I drive the PWM pin of the ISL6613 with this PWM signal from a function generator (images 2,3) and the  the PWM signal from the function generator was sinking. I measured the two other ISL6613 and the UGATE pins and LGATE pins had at UGATE 12.5V (in respect to ground) & LGATE 10.57V. Then I desoldered only the PWM pins of these two mosfet drivers and the signal from the function generator was OK and the step-down circuit worked (images 4,5,6) so the problem I believe is in the circuit before the mosfet drivers.

Below (image 6) I tried to make an analysis of the ISL6565 block diagram in order to understand what is this that prevents the PWM pulses to start at the PWM outputs even now (with CPU out) where I have the correct REF voltage (1.1V).
*VDIFF output is the VSEN input multipied x1.
*UVP comparator’s output is: (+In + 200mV) > VDIFF -> Vout=1 (High level)
For Good Mainboard: (1.34+0.2V) > 1.3V -> Vout=1
FMWNCPU: Faulty Mainboard With no CPU
For FMWNCPU Mainboard: (1.09+0.2V) < 2.55V -> Vout=0

*PGOOD output (is an indication of the end of soft-start) is the true table of NOR gate where “A” input is the output of the UVP comparator and “B” input is the output of the “SOFT-START AND FAULT LOGIC”.
For Good Mainboard: A&B must be “0” in order the output will be high (0.49V – from the datasheet table at page 9… PGOOD Max low voltage=0.4V). But the output of the UVP comparator I have calculated/assumed it “1”, so what am I missing here?

COMP – E/A(Error Amplifier) output is:
(+IN=REF) > FB -> Vout=0
(+IN=REF) < FB -> Vout=1
For Good Mainboard: 1.34V < 1.35V -> Vout=0 (the difference between two values seems to me very small)
For FMWNCPU Mainboard: 1.09 < 2.65V -> Vout=0V
The E/A comparator (gives “1” or “0” when all are OK?... how can I sure for this?

FB input is a negative current proportional to output current II can’t tell what is this exactly… maybe an analogy would be for instance 1uA on FB pin will corresponds to 1A on the “uP LOAD” (page 6)

The Greek Sigma symbol in the circles (like the brown line on the comp pin) is an adder? How it works with digital logic “1” & “0”… or maybe the inputs of the adder are in analog and not in digital  values.

Output of the AND gate at the “SOFT-START AND FAULT LOGIC” as I understand must be “1” in order the soft start will activate when the power/VCC will apply on the chip. In order the AND gate output will be “1” the VCC must have 5V, the ENLL must have 0.8V and above (table – page 6) and the comparator with hysteresis must have a voltage above of 1.24V at the non-inverting input (EN pin), in order to give “1”.

The function of the OFS pin is not clear to me and also, I doubt if it is input or output).

Could anyone confirm or correct what I wrote above?


ICOMMON pin: When I touch this pin with the multimeter’s probe or with oscilloscope probe in order to measure the voltage on it the mainboards (Good & Faulty) shutdown).
I managed to measure the voltage of this pin with an x100 oscilloscope’s probe (image 8) at the fault mainboard and it was 1.26V and on the Good one was 1.25V.
When I desoldered the resistor from the ICOMMON pin (image 13) the CPU coils then start to have 1.57V and the REF pin of ISL6565 1.57V. When I resoldered this resistor back in place the CPU again have 1.55V and the REF pin of ISL6565 1.57V. Maybe the problem of the not working  ISL6565 was a cold solder joint?

The current from the BIOS battery is 0,54uA (in the faulty one).

The problem now is that still the mainboard doesn’t have image and when I remove the RAM the speaker doesn’t make any sound at all. I found the below (image 9) of a power sequence from the video that the “fsasdad” suggest me. Also, I checked with the oscilloscope the xtal of the chip (image 10) and I saw a signal so it has a clock. Any suggestions of what to check?


2X:
The modifications that I made with a different VID code.
dzonika9661:
Hey buddy i'm from discord LER group,

Does your pch and cpu heats up on your motherboard ?

we can eliminate the bios chip/firmware from the list of possible faulty components
2X:

--- Quote from: dzonika9661 on August 27, 2024, 08:40:03 am ---Hey buddy i'm from discord LER group,

Does your pch and cpu heats up on your motherboard ?

we can eliminate the bios chip/firmware from the list of possible faulty components

--- End quote ---

Hello,
I took a photo from the motherboard and the PCH temp is around 50celcius. Also, the motherboard heats (the voltage on CPU coils is 1.55V).
Any suggestions of what other to check?
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod