HP laptop P.S. stuffed with silicon? NO PROB!

[glutton4punishment]

I have a 19V 4.7A HP laptop P.S. I get this high pitched very faint ambulance like noise......WE-DO-WE-DO...you get the idea. Oh, yeah, and no power leaving the P.S.

So, like the annoying troublemaker I am (tinkerer/explorer) I open it up. And it's full of white silicon glue, so I can't see anything!

NO PROB! One boxcutter and ten minutes later, take a look at the pics!

The caps look good, nothing looks burnt out. But I WANT to fix it.

BTW, there is a black rectangular ?? with 4 prongs to the right of the 2 large power caps. What is that?

please help!

All I have is a DVM, no cap testing function.

[rogfanther]

Re: HP laptop P.S. stuffed with silicon? NO PROB!

To the right in the first picture, or on the second ? If in the second, that is a Bridge Rectifier. With the multimeter, test for shorts between its legs.

Also, try to get a clearer pic of the undersido, so that the labels in the ics can be seen.

[mockingbird]

Re: HP laptop P.S. stuffed with silicon? NO PROB!

You should replace the LTec caps. Most of the time they go out of spec without showing any signs.

[RJARRRPCGP]

Re: HP laptop P.S. stuffed with silicon? NO PROB!

Likely power cycling from going into protection mode, because of DC-side short.

Probably makes a sound like a rodent repeller.

Back in July, someone brought a ThinkPad with that problem, it was fried!
(I sniffed it around the keyboard.)

And when unplugged from the laptop input, that sound stopped.

[glutton4punishment]

Re: HP laptop P.S. stuffed with silicon? NO PROB!

To the right in the first picture, or on the second ? If in the second, that is a Bridge Rectifier. With the multimeter, test for shorts between its legs.

Also, try to get a clearer pic of the undersido, so that the labels in the ics can be seen.

thanks. It's the second picture, so I guess it's a bridge rectifier. Do I take it off the board to test?

If it is shorted, how can I buy a replacement if it has no numbers on it?

More pics to come

[glutton4punishment]

Re: HP laptop P.S. stuffed with silicon? NO PROB!

You should replace the LTec caps. Most of the time they go out of spec without showing any signs.

forgive me, but are those the two 400V 120uF caps, or the very small ones?

[glutton4punishment]

Re: HP laptop P.S. stuffed with silicon? NO PROB!

Likely power cycling from going into protection mode, because of DC-side short.

And when unplugged from the laptop input, that sound stopped.

Right, when I unplug the P.S. from the wall, the sound stops.

OK, but what do I do about a DC side short?

[glutton4punishment]

Re: HP laptop P.S. stuffed with silicon? NO PROB!

I would like to add in a clue (maybe). after getting bitten a few times, I decided to discharge the 2 large caps. (with a screwdriver).

I did the first one (the one on the left in picture #2) and got a really big spark and loud crack noise.

Then I did the second one, and got a very feeble noise and a few short weak sparks.

Does that mean anything?

thanks to all!!!!!!!

[mockingbird]

Re: HP laptop P.S. stuffed with silicon? NO PROB!

forgive me, but are those the two 400V 120uF caps, or the very small ones?

The small one near the two large ones, and the two medium size blue ones on the left side. They say "Ltec" on them in cursive.

[glutton4punishment]

Re: HP laptop P.S. stuffed with silicon? NO PROB!

The small one near the two large ones, and the two medium size blue ones on the left side. They say "Ltec" on them in cursive.

wow......you're good. I didn't see that in person holding it in my hand!

[budm]

Re: HP laptop P.S. stuffed with silicon? NO PROB!

So what DC Voltage do you get at the DC jack without the load?

[LLLlllou]

Re: HP laptop P.S. stuffed with silicon? NO PROB!

forgive me, but are those the two 400V 120uF caps, or the very small ones?

They're the ones that say "LTec".

[kc8adu]

Re: HP laptop P.S. stuffed with silicon? NO PROB!

the dc plug is shorted on that unit.very common.desolder the cord from the board and it will work if you have not damaged it.

[glutton4punishment]

Re: HP laptop P.S. stuffed with silicon? NO PROB!

the dc plug is shorted on that unit.very common.desolder the cord from the board and it will work if you have not damaged it.

I wish!! after I checked the voltage at the computer plug side, I checked the voltage at the pins at the P.S.

Zero voltage.

[budm]

Re: HP laptop P.S. stuffed with silicon? NO PROB!

Unplug the the power to the brick, then check the resistance reading on the pins (+/-) of the DC jack of the brick to see if it shows really Ohm reading.

[glutton4punishment]

Re: HP laptop P.S. stuffed with silicon? NO PROB!

Unplug the the power to the brick, then check the resistance reading on the pins (+/-) of the DC jack of the brick to see if it shows really Ohm reading.

First I checked resistance of the P.S. cable from the 3 wires of the board on one end until the end of the P.S. cable that plugs in to the laptop. There are two black wires and one white wire on the board that lead into the cable that goes to the laptop. One white and one black wire show continuity from their respective connection points on the board to the outer metal jacket of the P.S. cable. One black wire shows connectivity between the connection point on the board to the inner pin of the P.S. cable

Resistance between the inner pin and the metal jacket that plug into the laptop shows infinite .

[glutton4punishment]

Re: HP laptop P.S. stuffed with silicon? NO PROB!

The small one near the two large ones, and the two medium size blue ones on the left side. They say "Ltec" on them in cursive.

OK, I replaced the 3 caps. That wasn't the problem b/c I'm still getting no voltage at the output, and it's still making the beeping noise.

[budm]

Re: HP laptop P.S. stuffed with silicon? NO PROB!

What DC resistance do you get measured right at two legs of either one of the output filter caps sitting at the edge of the board?

[glutton4punishment]

Re: HP laptop P.S. stuffed with silicon? NO PROB!

What DC resistance do you get measured right at two legs of either one of the output filter caps sitting at the edge of the board?

what reaction do you get when you swallow a 1/4 cup of granulated Draino?

[budm]

Re: HP laptop P.S. stuffed with silicon? NO PROB!

A lot of power supply will put Zener diode for crow bar protection right at the output which will be in parallel with the filter caps, the Zener voltage will be 2~3V higher than the output voltage, it will crowbar the output and shorted itself out.
So far the symptom looks like the powers supply is trying to drive the shorted circuit (as other also had indicated) in the secondary side, unless it is the start up cap problem in the primary side (but with bad start up cap usually you will see some DC voltage pulses on the output filter caps).