Home » amperage » Page 2


Reviving a laptop

My Micron Transport LT (a rebranded Samsung Sens Pro 680) died on Friday. I wasn’t a happy camper. Just ask my wife.

But it’s working again today, and I learned something along the way.We’d gone out for a while, and when we got back, I sat down at the laptop and noticed Windows was complaining about low battery power. I didn’t think much of it–I just unplugged the AC adapter and plugged it back in, like I usually do when that happens.

Well, about five minutes into my session it died hard. And it wouldn’t power back up, no matter what I tried. Eventually I got the idea to test the AC adapter. I took the adapter to a known-good plug, switched my voltmeter over to DC, touched one lead to the barrel of the plug and one to the tip, and got a whole lot of nothing. I tried it with an AC adapter that I knew worked, and got a reading. Then I noticed the power cord going into the adapter looked just like the adapter for most portable radios. Hoping against hope, I switched the voltmeter to AC, touched it to the leads, and got disappointment.

110 volts.

Google to the rescue. I did a couple of searches and found places selling AC adapters for a Micron LT, but the prices were outrageous. The best price I found was $55, and most places wanted $70 or $75. I didn’t want to sink that much money into a six-year-old laptop–especially when I didn’t know if the AC adapter might have taken something else down with it. Since the laptop had run fine on battery power, I had a pretty good indication it hadn’t, but I didn’t know.

I found one place advertising original Samsung AC adapters for $20. But they were sold out, of course.

A search on the specifications printed on the AC adapter itself–19 volts, 3.15 amps–yielded devices that would work, but again at prices higher than I was willing to pay.

Finally I decided to search Ebay. Searching on "Micron Transport LT" didn’t yield much except some parts laptops, and substituting "MicronPC" and "MPC" didn’t help. All I learned was that a stripped 650 MHz LT with no drives, AC adapter, battery, or extra memory sold for about 50 bucks. That was encouraging. I could Frankenstein an LT back together if I had to.

So I searched on "Samsung Sens Pro 680" instead, and found some joy. Some prices were outrageous. But I found a seller in Hong Kong with original Samsung OEM units. I also found someone in Brooklyn, Laptopspower, with an aftermarket unit. The prices were comparable–around $35. Did I want to buy an identical replacement? Part of me said no–why buy something identical to something that broke? But the little guy on the other shoulder reminded me that the one that broke lasted six years.

Basically the decision came down to Hong Kong vs. Brooklyn. No question a shipment from Brooklyn would arrive faster, all other things being equal. So I took a chance on the aftermarket unit and placed my order on Sunday night.

It arrived today. I’m happy to say it’s bigger and heavier than the original. Remembering previous jobs, I know some sissy-boy executives would complain about that, but if you’re a dumb PC tech like me, you know that the weight of a transformer is a crude measure of its quality. Cheap electronics components weigh less than higher quality components, all else being equal. Besides, I’m burly enough to manage to carry a couple more ounces without grimacing.

Some other things going for the aftermarket unit: It has an indicator light, so you know when it’s getting power. This way I’ll have some warning if and when this one dies, and I’ll know to save my work. That would be worth 30 bucks right there, if I happened to be working on the right thing. And the amperage of this unit is 3.2 amps, not 3.15. That’s not a lot of difference, but more amps is better. The laptop will only draw what it needs, but higher capacity means a cooler-running, longer-lasting unit.

And, as a bonus, I learned that the LT’s CPU is removable and upgradable. Just look for an MPGA Pentium III. The catch is that the fastest chip the LT will take is 800 MHz, and it wasn’t produced in large quantities. An 800 MHz MPGA P3 runs about $80. My 700 MHz chip costs about $30. That’s an expensive 100 MHz upgrade. But it’s nice to know I can get more speed, if I’m willing to throw money at it. It used to be that the only way to get a faster laptop was to buy a new one, after all.

So my LT is back in business again, and I’ve learned something. That can’t be bad.

Replacing wall warts with PC power supplies

I wrote a long, long time ago about my adventures trying to find a wall wart for my old 8-port Netgear dual-speed hub. The other day I stumbled across a novel idea for a replacement.
I won’t rehash how you determine whether a unit is a suitable replacement–read the above link if you’re curious–but suffice it to say a $5 universal adapter from Kmart is fine for my answering machine or my cordless phone and can probably provide the 5 volts my Netgear needs, but my Netgear also needs 3 amps and the universal adapter I keep around can only deliver 20% of that. The beefiest 5v unit I could find at Radio Shack could only deliver 1.5 amps.

A PC power supply delivers 5V and 12V on its hard drive connectors. And PC power supplies deliver plenty of amperage: one of mine will deliver 25 amps on its 5V line, and 10 amps on its 12V line.

In a pinch, I could just obtain a suitable plug barrel that fits my Netgear from Radio Shack, clip the power connector off a dead CPU fan, and solder the plug to the red wire (5 volts) and a black wire (ground), put it in a PC, and use that to run my Netgear hub. The increased power draw would be equivalent to putting three typical PCI cards in the system. Just be sure to wire things right–reverse polarity can kill some devices.

Rather than using one of the PCs I actually use, it would be better to obtain a cheap microATX case, short the green and one of the black wires on the 20-pin motherboard connector with a paper clip, insulate the paper clip with electrical tape, and then wire things up to the drive connectors. Or, for that matter, you could use some of the other leads available on the 20-pin connector if you have a device that needs 3.3 volts (pinout here.) You could also just use a bare ATX power supply with a paper clip connecting the green wire and one of the black wires on the 20-pin motherboard connector, if you’re into the ghetto look.

An AT power supply would also work and it offers the advantage of being really cheap and common (here’s a nice writeup about an AT power supply’s capabilities), but most AT boxes require you to hook up enough 5-volt devices to chew up about 20% of its rating on that power rail before they’ll power up. I have a 200-watt AT power supply that delivers 20 amps on its 5-volt rail, so my 3-watt Netgear hub probably wouldn’t be quite enough on its own. So it might be necessary to either connect an obsolete motherboard to the power supply or connect a 1-ohm resistor between a +5 lead and ground, if you don’t have a plethora of power-hungry 5-volt devices to plug in.

But PC power supplies provide a cheap and commonly available way to replace odd wall warts, or at the very least, to reduce the clutter around the computer room.

Testing a blown AC adapter

All too often, people plug the wrong AC adapter into an electronic device. People just plug in the first adapter that fits, and usually when they do this, if the equipment wasn’t blown before, it is now.
They’re known by many names, most of them not affectionate: power bricks, wall warts… But you miss them when they’re gone.
Read More »Testing a blown AC adapter