Electronics > Repair

Mainboard with No Picture

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2X:

--- Quote from: fzabkar on July 15, 2024, 02:35:07 am ---Your datasheet links are broken.

https://www.renesas.com/us/en/document/dst/isl6612-isl6613-datasheet (ISL6612, ISL6613)

https://www.mouser.com/datasheet/2/698/intersil_fn9135-1277737.pdf (ISL6565A, ISL6565B)

What voltage do you measure at the REF pin of the ISL6565BCRZ? Are the VID pins all 1s (Vcore regulator switched off)???

--- End quote ---




--- Quote ---Your datasheet links are broken.

--- End quote ---
Thanks... I replaced the links.


--- Quote ---What voltage do you measure at the REF pin of the ISL6565BCRZ?

--- End quote ---
I measured all the pins from the ISL6565BCR (at the attached image). The ISL6565BCR have ENable signal but but the voltage at REF pin is zero.


--- Quote ---Are the VID pins all 1s (Vcore regulator switched off)???

--- End quote ---
Sorry but I didn't understand what do you mean with "Are the VID pins all 1s"

Thanks for your time and the suggestions.


P.S. One thing that I noticed at the faulty mainboard is (with no CPU fan) when I switch ON the PSU I hear a buzzing with a very low volume (like whisper) around the CPU.


fzabkar:
Look at page 14 of the datasheet.

VID4 - VID0, VID12.5 --> 101001 --> Vcore = 1.350V

VID4 - VID0, VID12.5 --> 010101 --> Vcore = 1.600V

This means that the REF voltage should be 1.35V for the working motherboard, and 1.600V for the faulty motherboard. Instead it is 0V. When the Vcore regulator is functioning properly, the feedback voltage (FB) should match the reference voltage (REF).

Is it possible that the REF pin is shorted to ground, perhaps via the bypass capacitor???

Edit:

The datasheet states that the REF output of the DAC has a 1K series resistor. Could it be that the chipset is pulling this pin to ground and disabling the Vcore regulator???

2X:

--- Quote from: fzabkar on July 16, 2024, 07:29:52 pm ---Look at page 14 of the datasheet.

VID4 - VID0, VID12.5 --> 101001 --> Vcore = 1.350V

VID4 - VID0, VID12.5 --> 010101 --> Vcore = 1.600V

This means that the REF voltage should be 1.35V for the working motherboard, and 1.600V for the faulty motherboard. Instead it is 0V. When the Vcore regulator is functioning properly, the feedback voltage (FB) should match the reference voltage (REF).

Is it possible that the REF pin is shorted to ground, perhaps via the bypass capacitor???



Edit:

The datasheet states that the REF output of the DAC has a 1K series resistor. Could it be that the chipset is pulling this pin to ground and disabling the Vcore regulator???

--- End quote ---



--- Quote ---Is it possible that the REF pin is shorted to ground, perhaps via the bypass capacitor???

--- End quote ---
I check the capacitor in REF pin and it was OK. I measured it in diode mode and it was 0.73V (0.74V in the working mainboard) and the capacitor (desoldered) is 22nF like in the working mainboard. Also, I disconnect completely the capacitor and did't work, I cut the trace before the the via and didn't work again (attached picture - at the image the capacitor is missing because I took the photo when I have desoldered it).


--- Quote ---The datasheet states that the REF output of the DAC has a 1K series resistor. Could it be that the chipset is pulling this pin to ground and disabling the Vcore regulator???

--- End quote ---
This 1K resistor is connected between REF pin and at the inputs of two amplifiers via two other "voltage multipliers". There is the possibillity internal the chip to have a short? I measured all the pins in diode mode with the multimeter and all the pins show me the same Volt except from the pin 5 (VID12.5) where it shows me 0.65V in all the faulty mainboards and 0.32V in the working one.



fzabkar:
I can't see any alternative other than replacing that IC. It seems like a strange fault, though. :-?

2X:
Hi,
I replaced the ISL6565BCRZ chip but the same thing again and all the voltages at the ISL6565BCRZ pins are the same. It is something that keep the outputs down. Do you beleive that If the problem is from current sense and if I disconnect the resistors that are for Isense (ISL6565BCRZ picture in red circle) maybe will work? Maybe the problem is on the mosfets or the mosfet drivers that are after the ISL6565BCRZ?

According to the block diagram of ISL6565BCRZ if I understand it right... the only stage that can disable the "DYNAMIC VID" is the "SOFT START AND FAULT LOGIC" and this can be triggered via OVP, ENLL and EN pins, so maybe the problem is at these pins somehow? The strange is tha the voltages are the same these pins with the working one mainboard (picture Voltages).


From ISL6565BCRZ  datasheet:
EN - This pin is a threshold-sensitive enable input for the controller. Connecting the 12V supply to EN through an appropriate resistor divider provides a means to synchronize power-up of the controller and the MOSFET driver ICs.
When EN is driven above 1.31V, the ISL6565A, ISL6565B is active depending on status of ENLL, the internal POR, and pending fault states. Driving EN below 1.14V will clear all fault states and prime the ISL6565A, ISL6565B to soft-start when re-enabled.

ENLL - This pin is a logic-level enable input for the controller. When asserted to a logic high, the ISL6565 is active depending on status of EN, the internal POR, VID inputs and pending fault states. Deasserting ENLL will clear all fault states and prime the ISL6565A, ISL6565B to softstart when re-enabled.

OVP - Overvoltage protection pin. This is an open drain device, which can be externally configured with a resistor to control an SCR to shut down the regulator.

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