I have a betty r6_mb with a similar short to ground at the drain of the left mosfet, even after removing both. It stopped working after water ingress, and there are a few minor rust spots on some of the caps. Do I need a multimeter that supports capacitance to confirm which specific caps are shorted? Even if the shorted cap is identifiable, is there a way to identify the expected value without the schematic?
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Betty?
https://www.youtube.com/watch?v=pz1rjq5emKY
To confirm, the left mosfet is the 2nd dcin mosfet on the board that is powering the main power rail? Or is it the side that mates with the DCin power adapter?
If it is the main power rail, this implies that a high side mosfet is leaking and is usually bad news. Remove all power. Meter in lowest resistance scale. Measure the resistance to ground of this same shorted rail.
What is the exact resistance in ohms?
Respectively, repeat this measurement at the inductor near the CPU on the board. Often, the high side mosfet will leak and pass onto the cpu rail, the high adapter voltage and will kill the CPU. -
It's the one labelled P039, further from DCIN, not sure which exact purpose it serves in the circuit. It's measuring 0.8~1.8ohm. At PL7, which is below the GPU and to the left of the CPU, it's 2.2ohm to ground, but the smaller PL5 and PL6 above the CPU are open with respect to ground.
It's a shame with all these fuses on the board none of them blew to protect the rest of the circuit, but I guess there's only so much you can do when it's water damage.
Thanks for your prompt reply
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Post pics of this area and label the parts you have referenced above. Fuses are slow to act. Often the silicon devices get the hit and fail before the fuse reacts.Comment
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Need to see a close up view of the mosfet region (P039) that was measured.Comment
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Review this thread (if not done already) - same case:
https://www.badcaps.net/forum/troubl...01953-no-powerComment
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I thought i had posted in that thread, i'm not sure how this conversation wound up as a DM.
I have some replacemenet MOSFETs on the way, i'm just worried if there's a short to ground on one of them. It looks like there's supposed to be 20v there.Comment
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Which pin on mosfet P039 is measuring the low resistance to ground?
source (1-2-3)
gate (4)
drain (5-6-7-8)
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Like I said above, the drainComment
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Inject 1 volt (not more) onto the drain pin and hunt for who is heating up.Comment
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Meter in resistance mode. Remove all power. One probe on the drain pin of the mosfet you suspect to be shorted. Other meter probe to ground (metal shield is ok).
What is the exact resistance in ohms?Comment
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.8 ohmsComment
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Can you post a pic of your meter when you are measuring this point? Wish to review the meter scale and units of measure.Comment
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I promise you it's ohms, not kiloohms or megaohms. 0.8 ohms.Comment
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Then there must be a current draw if the injection is done correctly. This is a direct short to ground or may even be ground.
ps: hate apple auto-correctComment
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Hello everyone, I recently found this badcaps site and super Learn Electronics Repair youtube channel. And I wanted to learn how to troubleshoot power supplies and VGA cards and how to practice soldering, since I already have a properly defective piece of them. I am currently trying to solve two problems:
I have a Gigabyte GV-RX460WF2OC-4GD type card. I managed to find the faulty MOSfet (AON6414A) on it, which I replaced. The card starts up, but after about half a minute, the MOSfet in the same position will be shorted again. Is it possible that the PWM controller driving the MOSfet... -
Hi, Would appreciate some help.
I have an Apple Late 2013 15" A1398 MacBook Pro with Logic Board 820-3662.
Get charger light but no fan spin or chime. No liquid damage.
Found PPBUS and VCORE both shorted to ground. Other rails were ok.
Removed VCORE MOSFETS U7310, U7320 and U7330. Found U7330 was in fact shorted.
With the 3 MOSFETS removed, get PPBUS and fan spin. VCORE is still hard shorted to ground (0 ohms).
Attempted voltage insertion on VCORE to locate short using bench supply set at 1.0 VDC and 4.95 Amps (max current for my... -
I've got an old Alienware M18x R1 which shorted out the charger whenever it was connected. Tracked down the short to two shorted caps and burned CPU power controller caused by a shorted mosfet on the CPU's graphic power supply.
I've replaced the faulty mosfet, two shorted caps and the CPU Power controller (NCP6151S52MNR2G).
Issue is now whilst there is no short if I attempt to power the system on the fans spin for a couple seconds there are no lights and no further action - the PCH is heating up but there is no CPU power coming out but there is an enable signal... -
I am trying to fix an iMac 2017 PSU, initially came with a blown fuse and shorted PFC MOSFET (6R199P). After visual inspection and some measurements I replaced the FET with a P20NM60 and tested with 100w series lamp, and it lasted 1 second before going into dead short. The PFC controller chip (NCP1605BG) and its passives appear fine (passives measure OK), but I do not know if there is a simple way of testing the NCP1605 as I wouldn't like to blind-replace it.
There was some slight blackening of the solder on the PFC controller passives so I reflowed them all with some flux. I am waiting... -
Hi All,
I have this MSI GTX-980ti Gaming Golden Edition. It had shorted mosfet on memory. Replaced the shorted i.e. Q47 PK616BA with 4C09N and the card ran fine for a month. Then suddenly again the same problem. This time when i replace it 4C09N or with replacement PK616BA (Aliexpress) it gets shorted. As soon as turn on the PC the PSU shuts down and the same mosfet Q47 gets short.
What should be the next step. Kindly guide.
The board view files for this gpu is available and attached. https://www.badcaps.net/forum/showthread.php?p=1237952...
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