Dell Laptop component level repair

"Mike S" wrote in news:47f96eab$0$5638$ snipped-for-privacy@cv.net:

I suppose you could note down all the ICs in the area of the jack and locate their spec sheets and find the one[s] that regulates the battery charging. The spec sheets usually have application notes with typical circuit diagrams.

--
Jim Yanik
jyanik
at
kua.net

I'm guessing that the DC input jack repair was less than successful.

I think it's likely that one or more layers of the pc board are not connected to the replaced jack. The charging circuitry appears to be good, since the battery charges in the docking bay. I'd be surprised if there was duplicate circuitry to recharge from that source, only a different connection to the same part of the circuit that gets power from the input jack.

Resoldering the DC jack might get it working again.

jak

Look carefully at the connector on the adapter plug. There is an outside metal contact. That's the ground. There's a concentric metal contact ring on the inside, which is the +19.5VDC. There's also a tiny center pin. The tiny center pin supplies some kind of handshake with the computer that informs the computah that it's the right power supply. If the center pin is broken somewhere, the handshake never happens, and the computer complains that it can't identify the power supply.

The most common point to break the center pin is in the plug at the end of the power cable. The center wire is tiny and breaks easily. Shove the laptop against the wall, bending the cable at a right angle to the connector, and you've got a broken center wire.

However, since you've gone through the exercise of substituting power supplies and verifying that they're good on a different Insprion 8500, methinks that it's not the adapter. That leaves the power jack on the motherboard, and associated circuitry.

Well, if it's not the jack or the connection, then there's a broken trace somewhere. No schematic, no easy fix. Sorry.

3 boards in 5 years implies that you're doing something wrong with this laptop. My guess(tm) is that it has something to do with the docking station. I've had problems with those in the past. Perhaps the order and sequence that power is applied or removed. Perhaps a ground gets disconnected before the power. Dunno, just guessing.

(Note the docking station comments).

If you still have one of the old mother boards, you can possibly trace out where the wire to the center pin ends.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Thank you all for your replies. The other motherboards suffered different failutres (bad design) so I have several full sets of power supply components to work with. I don't think the problem is related to use of the port replicator because I just started using it to charge the notebook now. Never used it with the previous motherboards. The pinout of the adapter is helpful.

The plot thickens...

Sitting in my "get around to it" pile of dead laptops is an Inspiron

8600. It uses the same power connector as the 8500. The laptop is seriously intermittent. The problem (I've been told) is that the motherboard uses BGA (ball grid array) chips. These are ceramic chips, with solder bumps on one side. They are reflow soldered to matching pads on the motherboard. Bend the motherboard even slighly, and the solder connection breaks. My guess(tm) is that my junk pile has about 5 machines (mostly HP laptops) that have similar problems.

However, all is not lost if you're not afraid to do something radical. You can reflow solder the BGA chips by placing a metal can on top of the chip, filling it with alcohol and cotton, and setting fire to it. A heat gun is sometimes used to pre-heat and post-heat to slow down the too rapid temperature rise and fall. I use an optical IR thermometer to monitor the temperature. It's really easy to overshoot.

Lots more under "iBook repair"

I really like this one, but haven't tried the blow torch method:

I've done this with several BGA devices with about 50% success rate. It's not fool proof, but it's better than a dead or intermittent laptop. No guts, no warranty, no gain.

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558            jeffl@comix.santa-cruz.ca.us
# http://802.11junk.com               jeffl@cruzio.com
# http://www.LearnByDestroying.com               AE6KS

Thats a cool trick. Sounds better than blasting it with a heat gun and blowing other componenents off the board. Have to try it on some junk boards and see how it works.

Mike

"Michael Kennedy" wrote in news:maSdnaCpbvYT32banZ2dnUVZ snipped-for-privacy@comcast.com:

....

Build a dam around the component with paper. You can use a hot air gun to remove or solder just one component, if you do things right.

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bz    	73 de N5BZ k

please pardon my infinite ignorance, the set-of-things-I-do-not-know is an 
infinite set.

bz+ser@ch100-5.chem.lsu.edu   remove ch100-5 to avoid spam trap

I found it really easy to overshoot. However, the failure is not melting components or torching the board. It's having the BGA "drift" or move sufficiently to short between connections. Some BGA chips are also designed to have some air gap under the chip. If I over compress this air gap to zero, I get more shorts caused by squeezing the solder bumps into each other.

That's the problem with the C-clamp method. It localizes the heat, but potentially squashes the solder bumps. The trick is apparently not to over tighten the C-clamp. (I haven't tried this yet).

I did my best by first injecting some "no clean" liquid rosin flux under the BGA before applying heat. The flux provided the necessary oxidation protection, but also provided some protection against shorting between pads.

Another trick I used it cut out the bottom of a somewhat larger diameter tin can to use as a heat shield. I place it around the burning cat food can. That fit inside the aluminum foil heat shield. The problem wasn't burning components. It was melting the plastic case because I was too lazy to remove ALL the plastic parts.

A few more tricks.

I had one success using a block of scrap aluminum on top of the chip and a propane torch. It was a fairly small diameter BGA array, where the cat food can was too large. Applying the heat about 1/2" above the chip was very useful to prevent torching the board.

I put a heavy steel bolt or two as a weight at the bottom of the burning can in order to keep it from moving around. Don't use a painted can. Try to find a can with a flat bottom to maximize the contact area surface. Use alcohol, not kerosene as some articles have suggested, unless you enjoy the diesel stench.

I tried using some silicon grease, which had an interesting advantage. When heated, whatever solvent is used to make it flow, gets evaporated. The remaining silicon is more of a powder than a liquid, which acts something like a glue. This kept the cat food can from moving around. I cleaned off the mess afterwards with alcohol.

I'll try to remember to do a video next time.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558