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Fixing an old IBM Thinkpad charger

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EvhCo2000

New Member
Hello everyone!

I'm away from home most of the day, and I'm in need of a small and sturdy laptop, so I decided to take my ol' T43 from the basement and blow that dust off. The only problem is that the charger has been "ripped" a few years now (can't remember the reason) and I'm having trouble connecting them back togheter.
Here are two photos showing the ripped cable:



The adapter's green and the black cable were already tangled togheter when I found the charger.
What troubles me is that the cable going from the adapter has four cables, while the one going to the laptop only has two. I tried connecting the adapter's red to the input's white, and the adapter's green and black to the input's black, but that would simply NOT charge the battery. On the adapter, there is one actual cable that has no color, and wrapping it around the red cable would trigger the adapter's short-circuit protection (the relay would start tickling).

I know I suck at explaining, but I hope there's someone who can help me. I wouldn't wanna smoke up my laptop's battery (since this happened before).
Thanks a lot!

<Mod edit: Please do not post links to external image hosting websites. Embed the image within the message>
 
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spec

Well-Known Member
Most Helpful Member
Hi EC,

The Lenovo T43 is a great laptop- I had one for a few years. Update: it was a T42 but I think they are similar

You picture is confusing. It shows three cable ends but you are describing just one cable. Could you please clarify.

spec

PS: You can get the T43 schematic @ http://www.repairalaptop.com/ibm-t43-free-laptop-schematic/
 
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spec

Well-Known Member
Most Helpful Member
Just some information: the T43 requires a 16V, 4.5A (72W) power adapter

spec
 

EvhCo2000

New Member
Hi EC,

The Lenovo T43 is a great laptop- I had one for a few years. Update: it was a T42 but I think they are similar

You picture is confusing. It shows three cable ends but you are describing just one cable. Could you please clarify.

spec

PS: You can get the R43 schematic @ http://www.repairalaptop.com/ibm-t43-free-laptop-schematic/
Hi, spec! Thanks a lot for replying!
The cable from the lower part of the picture is the end that goes into the laptop's charging port (so that round silver plug is part of the cable end near it). The cable end in the upper part of the picture is the one coming from the actual adapter.

The adapter, as well as all the cables involved are the stock ones that arrived in the same package as the laptop.

Hope this helps. Thanks once again :)
 

spec

Well-Known Member
Most Helpful Member
Hi, spec! Thanks a lot for replying!
The cable from the lower part of the picture is the end that goes into the laptop's charging port (so that round silver plug is part of the cable end near it). The cable end in the upper part of the picture is the one coming from the actual adapter.

The adapter, as well as all the cables involved are the stock ones that arrived in the same package as the laptop.

Hope this helps. Thanks once again :)
No problem

Thanks for your response. I think I understand now what your picture shows.

At the laptop end the inner contact of the power plug connects to the white wire.

The the outer barrel of the laptop power plug connects to the screen.

At the power supply end the red wire connects to 16V and the screen connects to 0V.

Forget about the green and black wires. They are used on some mains adapters to inform some laptops what power the mains adapter is. The T43 does not use this.

All being well, about five minutes after connecting 16V power, the laptop should settle down and you will have a functioning T43. But you may have to reconfigure the BIOS or even remove and reconnect the back up battery. Or the backup battery may need renewing.

Did you prize the mains adapter apart with a hot knife, because the two halves of the mains adapter are usually glued together?

A common fault with those adapters is that the adhesive holding the torodial inductors to the printed circuit board lets go and the weight of the inductors fractures their self leads. So best to check that all inductors are firmly glued.

Also, make sure that non of the leads of components are shorting to to the leads of adjacent components- another common fault.:)

There is also a possible problem with the mains connector on those adapters, but I wont go into that for the moment.

spec
 
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EvhCo2000

New Member
Hi, spec!
I've done as instructed, but the laptop doesn't seem to be charging.

The cable end on the left part of the photo comes from the adapter.

The charger lights up and there IS current going to the plug (as I've accidentally touched the black'n'green cables to the red one, and it sparked). The battery is not damaged either (as it lights up the PC for 2 seconds before succumbing to its lack of power).
 

atferrari

Well-Known Member
Hi, spec!
I've done as instructed, but the laptop doesn't seem to be charging.

The battery is not damaged either (as it lights up the PC for 2 seconds before succumbing to its lack of power).
Could we say sensibly worn out, unable to take the charge it was initially designed for?
 

spec

Well-Known Member
Most Helpful Member
Hi, spec!
I've done as instructed, but the laptop doesn't seem to be charging.

The cable end on the left part of the photo comes from the adapter.

The charger lights up and there IS current going to the plug (as I've accidentally touched the black'n'green cables to the red one, and it sparked). The battery is not damaged either (as it lights up the PC for 2 seconds before succumbing to its lack of power).
Do you have a multimeter?

If so can, you check that there is around 16V on the center of the plug and OV on the outer barrel of the plug (actually measure on the plug)

(Note that all the laptop needs to work is around 16V.)

spec
 

spec

Well-Known Member
Most Helpful Member
Some more information.

When you have definitely established that there is 16V on the cable plug as described above, unplug the power plug from the laptop and remove the laptop battery.

Then plug the mains adapter in. Wait about 5 minutes. Then try to boot the laptop.

spec
 

spec

Well-Known Member
Most Helpful Member
The next move would be to disconnect the power adapter wires from the plug cable.

separate all four power adapter wires, red, screen, black and green.

Connect the positive of a multimeter to the red wire.

Connect the common (negative) lead of the multimeter to the remaining three wires in turn. Do any connection give a voltage reading of around 16V?

spec
 

EvhCo2000

New Member
Good morning, spec!
I used the multimeter, and there were exactly 16 volts on the adapter (maybe oscillating down to 15 and up to 17 sometimes for a second), and then I connected the multimeter's positive to the red wire.
And then connected the remaining cables one by one to the negative.
THEY ALL RETURNED 14-15 VOLTS.
This is getting interesting.
Thanks a lot for the help so far!
 

EvhCo2000

New Member
EDIT: We're getting closer now.
I connected the red wire to the multimeter's red, and the screen to the negative (all these while the adapter and the plug were connected togheter) and it returned exactly 16v as it should (and inverting them would show -16V, so at least we know the connections are right), but no current is going to the plug. None at all.
 

spec

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Morning to you EC,

EDIT: We're getting closer now.
I connected the red wire to the multimeter's red, and the screen to the negative (all these while the adapter and the plug were connected togheter) and it returned exactly 16v as it should (and inverting them would show -16V, so at least we know the connections are right), but no current is going to the plug. None at all.
Can you try this:

With your multimeter set to the lowest resistance range and the T43 power cable (with the plug on the end) completely disconnected, can you make these resistance measurements:
(1) between the plug center and outer.
(2) between the screen and white wire
(3) between screen and plug outer
(4) between white wire and plug center

spec
 

EvhCo2000

New Member
Done as instructed, partially.
White wire and plug center shows a resistance oscillating between 27 and 30.
However, after that, the multimeter wouldn't show any resistance at all between the other cables (and not even between the white and the plug center, which I've done earlie). It simply shows 1 (OL equivalent, if I recall correctly). Adjusting the range wouldn't fix this issue.
 
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spec

Well-Known Member
Most Helpful Member
Done as instructed, partially.
White wire and plug center shows a resistance oscillating between 27 and 30.
However, after that, the multimeter wouldn't show any resistance at all between the other cables (and not even between the white and the plug center, which I've done earlie). It simply shows 1 (OL equivalent, if I recall correctly). Adjusting the range wouldn't fix this issue.
OK - it is likely that the cable with the plug on it is faulty- this is not uncommon.

What you can do is cut the cable to the plug about 40 cm from the plug.

Bare the white wire and the screen and test that there is a low resistance between the plug inner and the white wire.
Then check there is a low resistance between the screen and the plug outer.

My bet is that they will be open circuit. If so you can repair the connections- I have done this many times. In fact, the the plug on this Lenovo T520 has been repaired several times.

The simple solution though would be to get a new plug with cable fitted or even a completely new mains adapter- neither item is expensive.

spec
 

EvhCo2000

New Member
Since I've never worked with currents bigger than 12V (Arduino, mostly), I'd rather not fiddle with the charger's "inners" right now.
My dad has a Lenovo, a completely different and MUCH newer model, but...guess what...the charger fits perfectly, so my T43 works just fine now.

I can't thank you enough for all your help. I know my lack of knowledge made this much harder, but I may have learned a thing or two on the way.
Stay safe!

-EC
 

spec

Well-Known Member
Most Helpful Member
Since I've never worked with currents bigger than 12V (Arduino, mostly), I'd rather not fiddle with the charger's "inners" right now.
My dad has a Lenovo, a completely different and MUCH newer model, but...guess what...the charger fits perfectly, so my T43 works just fine now.

I can't thank you enough for all your help. I know my lack of knowledge made this much harder, but I may have learned a thing or two on the way.
Stay safe!

-EC
Hi EC,

I was not asking you to fiddle with the chargers innards- just the cable with the plug on one end.

Make sure that your Dad's mains adapter outputs 16V or thereabouts. Later IBM power adapters are 20V.

spec
 
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