Will do but can you show me where Source & Drain are on this chip as it has 2 gates and 3 pins one side and 3 on the other. Thanks.
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Sure - see attached. Get a bearing of pin # 1 and locate the belly pads that will be visible on the North and South of the body as shown in the datasheet here:
Pin # 1 = DOT / DIMPLE = Top Left of the mosfet and the first pin is the G1 pin. Then count in a 'U' counterclockwise direction for the rest of the pins.
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OK thanks for that. 😀
Source to Drain - 43K ohms
Source to Gate 1 - 78K ohms
Source to Gate 2 - 2.4M ohms
Gate 1 to Drain - 1.34M ohms
Gate 2 to Drain - 4.7M ohms.Comment
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Just found another MOSFET below the one I just measured (with a coil between it) and its exactly the same QA3112
Source to Drain - 1.2M ohms
Source to Gate 1 - 1.5M ohms
Source to Gate 2 - 2.4M ohms
Gate 1 to Drain - 180K ohms
Gate 2 to Drain - 3.6M ohms.Comment
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The measurements with kohms are of concern. I would consider to source some spares and replace these parts. You can also flux each (make a note of their location #1 position first); remove off the board and then test each when the parts are on your work bench. Confirm is the measurements remain this low.Comment
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I took the mosfet off and the readings are reading OLComment
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I think I might change the MOSFET anyway. I have some old boards but none of them have a QA3112 on them but I found a board with 22CF FDMS3660S MOSFETs which looks similar. Could you compare them and let me know if they would be suitable? Many thanks.
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Anyone?Comment
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The replacement looks suitable - not as high current drain support as the original but is worthy of testing. Same pinout, etc.Comment
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Many thanks will give it a go.Comment
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Well I changed the MOSFET and the laptop is still doing exactly the same!! On and off every 3 seconds. So frustrating.
Is there anything else I can try? I'm determined to get this going.Comment
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Do you ever see any text / graphics on the display during the 3 seconds the power is on? You may have a dead CPU.
Remove all power / no battery. Meter in resistance mode (not diode mode). Measure the resistance to ground of each inductor. Checking for a low resistance measurement. Post any suspects.Comment
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No text and no backlight.
7 inductors on the board.
1 - 0.5K ohms
2- 1.10K ohms
3 - 37K ohms
4 - 0.8K ohms
5 - 0.7K ohms
6 - 0.7K ohms
7 - 36K ohmsComment
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Board with the inductors numbered.Attached FilesComment
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Seems a bit low to me but then I don't really know anything about this.Comment
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Can anyone help?Comment
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The screen seems to blackout and stay black, but with a flashlight I can see the display.
With my Playstation 4 connected via HDMI, and running a game I can hear sound.
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