Someone brought me a Dell laptop that had a loose power jack inside (power jack on a cable, not soldered to motherboard). Once disassembled found one of the wires was broken off the power jack. I replaced the jack and it won't turn on, but the metal shell of the jack inadvertently touched the metal hinge and suddenly it got power. I checked voltage from the metal chassis ground and the circuit ground and I get over 14V ? Has anyone seen this before? Typically is it some kind of filter cap that shorted? Very strange...
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Re: Dell Laptop - over 14V between Chassis Ground and Circuit Ground?
I should mention that this Dell Inspiron 7591 actually powered up and entered Windows when pressing the metal exterior of the power jack (circuit ground) to the metal hinge (chassis ground) but once I pulled it away the computer shut off. Very strange, so I measured voltage between chassis ground and circuit ground and found over 14V. Somehow voltage is live between the 2 ground points. Looks like the motherboard will need to be replaced, but just wondering if this is a common failure - live voltage on ground? -
Re: Dell Laptop - over 14V between Chassis Ground and Circuit Ground?
Not sure, looks like the ground is floating. Could you check the negative terminal at the board for dry joints ? Also try attaching the negative terminal to the USB metal housing or similar. Given that it boots fine, I don't think the motherboard is faulty. There are lots of other negative terminals like the copper on the board surrounding screen holes etc.Comment
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Re: Dell Laptop - over 14V between Chassis Ground and Circuit Ground?
Check continuity between Ground of mb to ground pin on dc jack connector.Comment
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Re: Dell Laptop - over 14V between Chassis Ground and Circuit Ground?
Yousuf, to clarify the situation. I found original power jack was badly damaged and the red positive wire broke off. Installed a new power jack the board is dead - no power, no charging light, nothing. This laptop has the power jack mounted under the hinge, so the hinge is flipped up out of the way. While testing, the power jack outer metal casing touched the hinge and I found the charging light lit. Separated the power jack from the metal hinge and the charging light went out. Each time I touched the power jack outer casing to the hinge I saw power - and yes I was even able to power up and enter Windows once. So I started checking a few voltages on the power jack and found that both the circuit ground (including the power jack metal outer casing) and the laptop chassis ground has over 14 volts? Now I haven't ever tested voltage between the ground points on any other laptop, but this seems strange.
mcplslg123, I believe I checked continuity between the grounds, but don't remember the testing points I used. I'll check and report back a little later. Thanks for the suggestion.Comment
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Re: Dell Laptop - over 14V between Chassis Ground and Circuit Ground?
I removed the motherboard from the laptop case. Testing continuity between ground on the AC jack and ground on the motherboard fluctuates somewhere around 270 kohms but after checking a few times it seems erratic. Next time it gave me around 23 mohms and climbing.Comment
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Re: Dell Laptop - over 14V between Chassis Ground and Circuit Ground?
Its DC jack and thats what you mean by saying AC jack?? Anyway, the resistance between Ground pin of dc jack and Ground point on mb should be 0 Ohms. Are you sure you have correctly identified the gnd pin on dc jack?? Id the dc jack soldered on mb or it connects thru a cable??Comment
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Re: Dell Laptop - over 14V between Chassis Ground and Circuit Ground?
mcplslg123, yes I mean a "DC" power jack (sorry, it was late). It's on a cable, not soldered on the motherboard. Here is a picture of the style of jack.
I checked the metal on the jack and I also checked on the black wire (of course it's the same). Yes, checking resistance between the black wire on the power jack and a ground trace on the motherboard is not giving 0 ohms like it should. Giving erratic readings, like a capacitor would. Something is shorted.... but this seems like a strange short!Attached FilesComment
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Re: Dell Laptop - over 14V between Chassis Ground and Circuit Ground?
Put a jumper wire from GND of mb to black pin of dc jack and check again.Comment
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Hi friends of electronics
What you see in the video and pictures attached is the circuit for charging the batteries of a DC motor.
The problem is that this circuit cannot charge the batteries (3 1800mAH NiMH batteries) any more. When the circuit was OK, its green LEDs lit up one at a time to show that the batteries have charged more. But now that the circuit is flawed, LEDs light up as you see in the video and at the same time successive beeps are heard.
Please help me fix this circuit.
(the datasheet of the IC: https://pdf.datasheet.live/28...
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