Re: 820-3332 POSTS but has short damage 12V8 to 3V3
Thanks for the info. Read through your thread, the RAR files and watched the video. I'm concerned the conversion might not work in this case since I can't get any video even if I try to start in Recovery or Safe mode where the processor defaults to the integrated GPU.
barry101
Senior Member
Last Activity: 11-29-2024, 11:53 AM
Joined: 08-17-2019
Location: Cumming, GA
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Re: 820-3332 POSTS but has short damage 12V8 to 3V3
Interesting suggestion and it sounds promising but while the laptop seems to boot and access the drive, I can't get anything on the internal or external display. I've tried safe mode and recovery mode with internal and external displays and no luck. Without a display, how do I access terminal mode to use the PMSET command? Or do I need to remove and modify the EFI/BIOS to disable the discrete GPU?Leave a comment:
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820-3332 POSTS but has short damage 12V8 to 3V3
Hi
I have an 820-3332 that chimes, has fan spin and has disk activity (see indicator light on external drive flashing) but nothing appears on either internal or external display.
U8900 already re-soldered twice with no improvement.
For the reasons below, I'm pretty sure the GPU and/or Graphics MUX is fried but since the board has signs of life, I would appreciate any guidance that can be offered before I throw the board into the parts bin.
First the bad news: There was one spot of corrosion that had connected 12V8 at C8925-1 (PPVIN_S5_HS_GPU_ISNS... -
Re: 820-01814 Won't power on, PP5V_G3S shorted
All of that from a connecting a thumb drive!Leave a comment:
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Re: 820-01814 Won't power on, PP5V_G3S shorted
Hi,
Attached is a photo showing the L7600 and L7660.
However, I found the problem! I removed L7660 completely and the empty pad was getting hot. Using some alcohol, found that C7605 was shorting PP5V_G3S to ground. Removed and replaced C7605, reinstalled original L7600, L7660 and U7650 and problem solved.
Since C7605 is right next to L7660, I suspect the heat felt in L7660 even when lifted was being thermally conducted from the neighboring C7605 pads. I'm sure I felt C7605 with my finger...Leave a comment:
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Re: 820-01814 Won't power on, PP5V_G3S shorted
Removed U7650 TPS51980A. PP5V_G3S still shorted to ground.
Tried injecting voltage again on 5V side without TPS chip. L7660 still got hot.
Lifted L7660 pin 2 in an attempt to stop any path through L7660 to see affect on 5V side. PP5V_G3S still shorted to ground.
Injected voltage again at L7600 and, I couldn't believe it, but L7660 still gets burning hot almost immediately. There is no voltage on L7660 pin1. Pin 2 is definitely not touching the pad. Checked with a voltmeter and an oscilloscope...Leave a comment:
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Re: 820-01814 Won't power on, PP5V_G3S shorted
Performed diode mode comparison for the TPS51980A on this 820-01814 board vs TPS51980 on a good 820-3332 board.
5V side discrepancies:
Pins 2 and 8 read 0 volts instead of .41 and .40 respectively since PP5V_G3S is shorted.
Pin 7 read .31 instead of .80 but would have read differently if L7600-1 was not currently lifted due to the short.
3.3V side discrepancies:
Pin 17 and 18, P3V3G3H_CSN2 AND _CSP2 respectively, read .40 and .71 instead of .13 and .52 respectively. However, I am...Leave a comment:
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Re: 820-01814 Won't power on, PP5V_G3S shorted
Sorry about the duplicate message, didn't realize the thread went on a new page, thought the first of the two messages didn't go out.Leave a comment:
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Re: 820-01814 Won't power on, PP5V_G3S shorted
L7600 - 1 to PPBUS_HS_OTH5V 6K and rising
L7600 - 1 to PP3V3_G3H_T 18K
I have some 2012 820-3332 donor board with TPS51980 vs. the TPS51980A on this board. Is it ok to use that part?
Before proceeding to remove the TPS, I will try some diode mode comparisons to the 820-3332 board and see if that shows anything interesting. I'll report back later today.
By the way, did the MOSFET reading show anything of interest?Leave a comment:
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Re: 820-01814 Won't power on, PP5V_G3S shorted
L7600 pin 1 to PPBUS_LS_OTH5V 5 to 6K and rising
L7600 pin 1 to PP3V3_G3H-T 18K
Measurement taken at L7600 pin 1 pad since L7600 is lifted at that end.
Did the MOSFET readings show anything?
I have some 820-3332 donor boards that have a TPS51980 as opposed to the TPS51980A on this board. Ok to use that version of the part?
I'll try some Diode Mode comparisons to the 820-3332 donor board and see if that shows anything useful. Will get back later today.Leave a comment:
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Re: 820-01814 Won't power on, PP5V_G3S shorted
Could this explain both the short to ground on the 5V L7600 and power heating the 3V L7660?
What if:
PP5V_G3S short to ground is internal to U7650 on CSN1
U7650 has an internal path from CSN1 to CSP2
Current flows through R7692 to L7660 and then out to the load.
This would happen even if L7600 is lifted on the load side.Leave a comment:
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Re: 820-01814 Won't power on, PP5V_G3S shorted
Re-ran U7600 resistance measurements being sure to discharge the gate and have the black probe on the gate. Same results repeated here for ease of comparison with U7660.
UPPER MOSFET:
SOURCE TO DRAIN (PIN 4 TO PIN 1): 6.5K RISING TO ABOUT 10K AND STILL GOING UP
SOURCE TO GATE (PIN 4 TO PIN 3): 90K
GATE TO DRAIN (PIN 3 TO PIN 1): 100K
LOWER MOSFET:
SOURCE TO DRAIN (PIN 4 TO PIN 9): 5.6K
SOURCE TO GATE (PIN 4 TO PIN 5): 93K
GATE TO DRAIN (PIN 5 TO PIN 9): 88K...Leave a comment:
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Re: 820-01814 Won't power on, PP5V_G3S shorted
Here are the requested resistance readings with L7600 load side lifted:
UPPER MOSFET:
SOURCE TO DRAIN (PIN 4 TO PIN 1): 6.5K RISING TO ABOUT 10K AND STILL GOING UP
SOURCE TO GATE (PIN 4 TO PIN 3): 90K
GATE TO DRAIN (PIN 3 TO PIN 1): 100K
LOWER MOSFET:
SOURCE TO DRAIN (PIN 4 TO PIN 9): 5.6K
SOURCE TO GATE (PIN 4 TO PIN 5): 93K
GATE TO DRAIN (PIN 5 TO PIN 9): 88K
Does U7600 matter since the short is on the load side of L7600?Leave a comment:
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Re: 820-01814 Won't power on, PP5V_G3S shorted
Thanks so much! Appreciate your help!Leave a comment:
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Re: 820-01814 Won't power on, PP5V_G3S shorted
The injection point was at the output of L7600, not the input to L7660. That's why I don't understand why L7660 go hot. Please the photo I attached to the previous post.Leave a comment:
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Re: 820-01814 Won't power on, PP5V_G3S shorted
Closer examination of the traces to the fan connector pin 1 shows PP5V_G3S not going under the warm/un-occuppied area of the board. It passes to the left of L7660 so I'm not sure why that spot got warm. That leaves the question as to why did L7660 get so hot?Leave a comment:
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Re: 820-01814 Won't power on, PP5V_G3S shorted
[ATTACH]311694[/ATTACH]
The attached photo shows the warm spot at the tip of the probe. L7660 and the no-stuff fan connector (I presume that is what the pad is for) are also shown.Re: 820-01814 Won't power on, PP5V_G3S shorted
[ATTACH]311694[/ATTACH]
The attached photo shows the warm spot at the tip of the probe. L7660 and the no-stuff fan connector (I presume that is what the pad is for) are also shown....Leave a comment:
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Re: 820-01814 Won't power on, PP5V_G3S shorted
Lifted L7600 load side. Load side was shorted to ground.
Injected 1V on load side and set current limit to 4.9Amps. Read about 0.6V at injection point and drew about 2.3 amps.
After about 10 minutes the only place that got to 135 degrees F was an empty spot midway between L7660 and U7660 about 1/4" toward fan cutout. No components at that location on either side of board.
However, L7660 itself got burning hot to the touch although the infra red temperature gauge only showed it to be about...Leave a comment:
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Re: 820-01814 Won't power on, PP5V_G3S shorted
Got it, thanks. I'll let you know how it turns out.Leave a comment:
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Re: 820-01814 Won't power on, PP5V_G3S shorted
I'll try that. Do you recommend lifting the inductor to determine which side is shorted first and inject voltage onto the shorted side only or just leave the inductor in place?Leave a comment:
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