HP Power Brick

[rigeback]

Got a problem here with my laptop HP Delta power brick, the other day noticed the led had died so opened the box and starting checking the caps voltages etc, the high voltage is present but nothing on the DC side. All caps are in good condition and the are no burnt parts. Cold resistance tests indicate that 2 ceramic caps on the high voltage side are open both sides inter connected with zener diodes?
I will post some pictures if required but I think the problem could be solved with some indication of possible causes.

[budm]

Re: HP Power Brick

Pictures will help a lot.

[PeteS in CA]

Re: HP Power Brick

Ceramic capacitors measured out of any circuit will look like an open circuit. Measured in-circuit your ohm meter will see whatever resistance there is, if any, in the surrounding circuit. Several different topologies could be used in an adapter, so pictures are a necessity. Also, stating where you made your measurement is necessary. When you say, "... the high voltage is present ...," do you mean AC is present at the inlet, or do you mean there is rectified DC on the I/P 'lytic?

If this is a self-oscillating flyback (what Delta calls "ring choke"), look for bad solder joints at the transformer pins, the switch device leads and the leads of the current sense resistor in the emitter (or source) circuit of the switch device. Also, when you apply power, do you hear a repetitive chirp or click sound? If so, the adapter is trying to start up and is either in current limit or output over voltage protection.

[rigeback]

Re: HP Power Brick

Got the pictures and took a few more measurements, on the AC side I've got the 240V on board and 460V across the main filter cap. The problem might be with IC3 since there is a fluctuating 150V - 460V on both sides of C21 which then connects with IC3 on 2 middle pins nearest, on the opposite side of IC3 I couldn't get any reading. On D2 there is 40V on the cathode. All readings taken using the main filter cap ground. The mossfet near to RC39A has 460V on one pin marked red in pic-03.
The adapter seems to be running fairly warm but no no signs of anything burnt so far.

[rigeback]

Re: HP Power Brick

No there are no start up sounds what so ever, if fact it could well be the fly back since power is entering but nothing on the feed side. I checked the leads and wires and they seem to be good.

[rigeback]

Re: HP Power Brick

Might have a bad cap in front of the main filter cap, removed it and it still shows a short both ways, problem is I have a replacement 680uf 10V 105*c the original is 680uf 16V 125*C, will this be a problem?

[PeteS in CA]

Re: HP Power Brick

I didn't see any bad solder joints or other clues. It looks like it has active PFC, and with a rated power of 185 watts, I think it is not likely to be a flyback. As for the cap substitution, if the circuit voltage at that point is 12V, a 10V cap would cause trouble. But if the circuit voltage is under 10V, not a problem.

[Uranium-235]

Re: HP Power Brick

what the HELL kind of laptop uses 9.5A???!!! closest thing I've ever seen was a dell laptop/desktop hybrid that used like 8.5 and that thing was HUGE. 17' LCD, dual 2.5 HDD's

edit: correction: it was 7.7A, and it was an XPS M2010

http://www.dell.com/us/dfh/p/xps-m2010/pd

^^has a design flaw, the motherboard would keep dying, they replaced it like 4 times, before they gave this lady a more expensive and bigger top

[rigeback]

Re: HP Power Brick

The cap seems ok after comparing it with the old one and since I am only using a multimeter. Some thing is not switching either a mossfet or the ID switch which also illuminates the led.
I've attached a schematic for this adapter, I never thought it was going to be such a pain in ass until now, since the battery pack quit I started using the PC without the battery and this might have caused an overload although it does point out that after 2 minutes the charger will reactivate!

[rigeback]

Re: HP Power Brick

I think this explains what might be the problem although I was using the computer for a few days with a battery, will try fitting a battery tomorrow....

An independent current source with zero current is identical to an ideal open circuit. For this reason, the internal resistance of an ideal current source is infinite. The voltage across an ideal current source is completely determined by the circuit it is connected to. When connected to a short circuit, there is zero voltage and thus zero power delivered. When connected to a load resistance, the voltage across the source approaches infinity as the load resistance approaches infinity (an open circuit). Thus, an ideal current source, if such a thing existed in reality, could supply unlimited power and so would represent an unlimited source of energy.

No real current source is ideal (no unlimited energy sources exist) and all have a finite internal resistance (none can supply unlimited voltage). However, the internal resistance of a physical current source is effectively modeled in circuit analysis by combining a non-zero resistance in parallel with an ideal current source (the Norton equivalent circuit). The connection of an ideal open circuit to an ideal non-zero current source does not represent any physically realizable system

[rigeback]

Re: HP Power Brick

what the HELL kind of laptop uses 9.5A???!!! closest thing I've ever seen was a dell laptop/desktop hybrid that used like 8.5 and that thing was HUGE. 17' LCD, dual 2.5 HDD's

edit: correction: it was 7.7A, and it was an XPS M2010

http://www.dell.com/us/dfh/p/xps-m2010/pd

^^has a design flaw, the motherboard would keep dying, they replaced it like 4 times, before they gave this lady a more expensive and bigger top

This is a HP ZD8000, I've never tajen much notice of the power pack until now and you're right its heavier than a desk top PSU, I'm looking at using another power adapter and hopefully the lower amp will drive the 17" monitor?

[momaka]

Re: HP Power Brick

Check the output voltage.
- If zero volts and steady, check that the output cord hasn't shorted internally (use multimeter to check resistance between [+] and [-] on the output plug).
- If not zero volts, but rather the voltage goes up and down, change the start-up cap (usually a small 10uF, 22uF, or 47uF electrolytic cap on the primary side).

[rigeback]

Re: HP Power Brick

Hi Momaka, good to see you back on the forum. No the Cord is fine first thing I checked and rechecked, unfortunately the is no DC power to the cord, I might change the start up cap anyway, I removed the resistor near the main cap R13 marked 0.13 Ohms and ran 12.90V through it, it holds at 0.17V so I guess its working correctly. There is also one of those DC Film Capacitors near the flyback which I want to take out of circuit.
I tried the laptop with another 19V - 2Amp power brick and its dead, disassembled it and I do not see anything burnt or shorted parts so far, one of the fan plugs was fairly loose so maybe it shut down due to this, this has not been a good week for power bricks or lap tops.

[kc8adu]

Re: HP Power Brick

short in the dc cord common in these.bad jack/plug causes heat and insulation melts.

[rigeback]

Re: HP Power Brick

On the back of the laptop it says a 19V - 9.5A or 7.1A to be used, if I hook it up 5A charger will it be too much load??
I'm figuring to modify the plug in to standard round pin if I fit in and use a multicharger.

[Toasty]

Re: HP Power Brick

460v on a cap series that only goes to 450v...?

You should have ~340v and no more than ~370v. (375v + 20% = 450v)

[rigeback]

Re: HP Power Brick

Oh it goes higher the meter went over 1000V as if the power has no where to vent, would this indicate the main filter cap is dry or on the way out?
One over part I'm curious about is the Gray rectangular box with a 'K' marked on top KEMT DC Film Capacitors, how often do these fail?

[ben7]

Re: HP Power Brick

Oh it goes higher the meter went over 1000V as if the power has no where to vent, would this indicate the main filter cap is dry or on the way out?
One over part I'm curious about is the Gray rectangular box with a 'K' marked on top KEMT DC Film Capacitors, how often do these fail?

oh, you must be measuring it wrong, or your meter is broken. You shouldn't get more than 360 volts. Make sure you are using DC setting too!

Also, using a power supply with a rated output of less than 7.1A will probably get overloaded at some point, if not right away.

-Ben

[b700029]

Re: HP Power Brick

Oh it goes higher the meter went over 1000V

If your meter is one with very high input impedance, that is enough to cause accumulated static to give false readings. Disconnect the meter, short the test leads together so it reads 0V, then put the test leads back into the circuit.

[Toasty]

Re: HP Power Brick

Bad/poor meter. Reading chopped or half-wave DC will do this.
Try it with a 470k, 1w resistor across the cap.

Failed main cap usually takes out the switchers.

Film caps do fail, but typically they are spectacular when they do.

See momaka's post re: startup caps.