Old HPDV8000 series motherboard problem

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Old HPDV8000 series motherboard problem

Postby cgowens » Mon Jan 05, 2015 12:33 pm

I've been trying to fix an old HP laptop for a friend and was looking for some advice. This computer will not power on, when you try, it makes a distinct clicking sounds (its not the hard drive) that's coming right from the AC power jack. If you plug the power jack in, the indicator light will flash once then shut off, but it will hold when a battery is inserted(will still not power up. makes same clicking noise)
thinking that its this particular fuse right by AC input that might be the culprit, I'm not getting any readings for a multimeter, and it looks blemished compared to other similar fuses on the motherboard (hell if it even is a fuse)
http://imgur.com/a/yma3A#2

These other two look fine, and I get readings from them
http://imgur.com/a/yma3A#1
http://imgur.com/a/yma3A#0

and here's just a full shot of the motherboard itself
http://imgur.com/a/yma3A#3

Am im completly full of $%^!@# and its somthing else? apriciate any help you guys will be able to give me
cgowens
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Re: Old HPDV8000 series motherboard problem

Postby Toby B. » Mon Jan 05, 2015 5:12 pm

I simply do not know enough about electronics (i.e. fuses and such), to determine if they are bad or not...

You mentioned a clicking noise.. Is it from the cord itself or the actual laptop?? Could be a beak in the wire or bad box/transformer (the black box in the middle of the cable).
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Re: Old HPDV8000 series motherboard problem

Postby Karlsweldt » Mon Jan 05, 2015 5:41 pm

Some references to ID markings on a circuit board:
A "C" would indicate a capacitor. A "D" would indicate a diode. A "ZD" would indicate a Zener diode.
A "Q" would indicate a transistor. An "L" for a Toroid, and a "T" for a transformer. An "F" for a fuse.
That "PD4" you note is not a fuse.. it is a power diode. Some are glass encased, most are epoxy encased.
If a diode is carrying too much current, it can 'pop' and destroy itself, or just exhibit what is shown for that "PD4".
A diode exhibits near infinity resistance to one current flow, near zero resistance in the opposite.. allowing only a positive or negative pulse to pass.
Depends on the voltage range it is designed for, and current. An AC power source has a zero center, then maximum positive, then zero again, and maximum negative.. then zero. That is one cycle. Diodes are commonly used for rectifying AC voltage to DC. Some are single diode designs, some two diodes, others four diodes. Half-wave, and full-wave respectively. Most diodes can be checked in-circuit, with a multimeter. Zener diodes need to be removed for testing, as they act as a near-short when reaching their rated voltage. Otherwise, a near infinity reading both ways.

That clicking noise you hear is likely a circuit breaker resetting, if more than 4 seconds between clicks. If more frequent, then could be a power pulse in a transformer, or the hard drive is attempting to spin up but cannot overcome friction.
Could also be a small DC cooling fan, attempting to spin.. but something is obstructing its blades.
For an AC mains fuse, the rating should be at least 250 volts if used on 120 volt circuits. 500 volt rated if used on 220 volt circuits. This is to ensure that no arc-over occurs if the fuse element does pop.
Most fuses are instant-blow, others have a tiny spring and bit of solder that melt at a certain temperature.. time delay fuses.
F@H.. to solve mankind's maladies.. in our lifetimes!
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Re: Old HPDV8000 series motherboard problem

Postby Mr T » Fri Jan 09, 2015 8:43 am

More than likely the graphics chip (needs a reflow). The clicking noise is usually the speaker. The other thing to look at is the screen inverter, but it is unlikely.
I have been programming on computers since the ZX81.
I am an apprentice trained Electronics Engineer with qualifications to back it up.
I have been repairing computers since 1996.
Yet to some people I still know nothing...
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