My laptop AC adapter stopped working and I don't know where is the problem

Thread Starter

rambomhtri

Joined Nov 9, 2015
462
Hi, my laptop AC adapter stopped working suddenly. I heard no "POP" neither saw any smoke, so I proceeded to measure things hoping to fix it quickly (probably the cable). The input cord carries those 230V just fine, so there is no problem with that one. However, I measured the output 19.5V DC and I was reading just a couple of hundred mV DC. So I thought it was just the cable, but I was wrong. I have just opened and disassembled the adapter and the output cable is perfectly fine, there's continuity all along from the soldered connection to the end pin, both outer negative and inside positive.

I've been trying to spot a damaged cap, no luck, everything seems to be fine. I see no black spots, no explosion marks, no burnt areas, no corrosion, no dirt or dirty connections... So I am running out of ideas. I am gonna share a picture of the back plate and front plate of the disassembled adapter, as well as a video with my macro lens so you can "navigate" all along the different parts. In the upper right corner and bottom left corner you can see 2 missing soldered holes. That's the shield/earth, the metal case that's covering everything.

These cost around $40-50, so it is a huge success if I detect the problem and fix it replacing something for $3. And I basically do it because I love to fix things instead of replace them, unless the replacement is notably more efficient and way faster/better. Not the case.

back.jpg

front.jpg

Video: https://streamable.com/yttu3y

Oh, by the way, the adapter has a blue LED, soldered next to the output cable, and it lights up when plugged, so it is really weird. I though that the blue light was an indicator that told us the there were 20V DC reaching the output cable. It could totally be simply that there are 120/230V in the input cable, which would be way less helpful to diagnose these kind of things. I can tell you the values of some cap or anything you ask.

Also... how do you safely discharge all the caps and possible devices that may store energy and are able to give it very quickly (dangerous to the touch)?
If it is one by one, using a resistor and knowing which pins you should touch... what if it was a board with dozens of them and you don't want to go one by one?
 
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Thread Starter

rambomhtri

Joined Nov 9, 2015
462
I see a few bad solder joints. The LED lights up only when the input is plugged in or else?
Thanks!

Where do you see bad solder joints?
These have not been touched, so it's very rare if they don't work because there's a bad connection. In all the years repairing stuff, a bad solder join that makes a device stop working creates some black/burnt stuff somewhere, specially in power related devices. It could be, point them out and I will check them or upload closer pictures, but I guess it's just a component that stopped working internally, without leaving any trace. A cap that didn't explode or swell.

The blue LED lights up whenever you plug it in to the outlet, of course. There's something going on that is keeping the 20V from reaching the output cable pins. I don't really know how to troubleshoot this anymore... I can only desolder components and measure, but... it would take hours and hours, it would be blindly because I see no damaged parts, besides some components are stuck in the solid white-yellow "glue", such as big caps.

I have not tried to measure voltage with the adapter powered, I am scared that I am literally in front, a few inches away with my face and hands, of something that is protected by metal plates, solid glue and a big chunk of plastic case. I guess the only danger would be a cap exploding, but I have never experienced that in real life, and I don't want to like this, with no control.
 
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Delta Prime

Joined Nov 15, 2019
1,326
Hello there! :)
With the unit unplugged disconnected from outlet.
1)450 volt capacitors short the pins with a 5 Watt one kilo ohm or higher resistor value, may spark.
2) T3. 15A 250V slow blow fuse check continuity beat good, no beep no good. Replace.
3)U1 acquired data sheet take note of pin out, power pins. Stop! report back!
 

Thread Starter

rambomhtri

Joined Nov 9, 2015
462
Exploding semiconductors are also fun.
Uh? Never heard of that. I though they would burn, not explode. How does that happen?

Is this related to your tripping breaker?
No, not at all, that tripping breaker post is from a friend's house, and I guess that even after I switched off the hot wire, the neutral was still connected to all the neutral circuit in the house, and basically to the breakers. When the tip of my iron, which is earthed, touched the neutral, that triggered the breaker. I still don't know if it was because there was a tiny current going on, or if the moment you short earth and neutral, even in my case if there were no current at all, it still triggers the breaker.

This post is about a power adapter suddenly stopping working, and how can I fix it.

Hello there! :)
With the unit unplugged disconnected from outlet.
1)450 volt capacitors short the pins with a 5 Watt one kilo ohm or higher resistor value, may spark.
2) T3. 15A 250V slow blow fuse check continuity beat good, no beep no good. Replace.
3)U1 acquired data sheet take note of pin out, power pins. Stop! report back!
Hi!
Where is the 450V cap? Oh the blue one?
The brown one is 420V. How do I know what's inside the yellow-white stuff, by the way?
Anyway, both brown and blue are discharged, the T3 is working fine (no resistance).

I don't understand number 3. What is U1? A voltage?
 
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Thread Starter

rambomhtri

Joined Nov 9, 2015
462
I see them all the time the top of the casing blows out leaving a crater. I have a IPM on the bench right now that you can see the 3 MOSFET dies. Pressure buildup following a shot circuit is usually the culprit.
Can you point me to a video?
I have see videos of capacitors exploding, and batteries, but nothing else. I wanna see other accidents with other components to know what's normal and what to expect.
 

Delta Prime

Joined Nov 15, 2019
1,326
My mistake! let me put it in another way. Any electrolytic capacitor you find in a laptop power supply above 35 volts, for safety while servicing the unit,it's good practice to discharge stored energy in the capacitor. When dealing with capacitors always consider them charged always handle them by the sides of the capacitor.
 

Thread Starter

rambomhtri

Joined Nov 9, 2015
462
My mistake! let me put it in another way. Any electrolytic capacitor you find in a laptop power supply above 35 volts, for safety while servicing the unit,it's good practice to discharge stored energy in the capacitor. When dealing with capacitors always consider them charged always handle them by the sides of the capacitor.
Yeah, I've done what you said, now what do you suggest?
Everything seems to be working so far... could it be the transformer coil that got broken and there's no secondary coiling continuity and that's why there is no 20V DC?
I don't know...
 

Delta Prime

Joined Nov 15, 2019
1,326
I see a lot of field technicians that blow the tips of their probes with caps
I have said nothing about probes I am not a field technician. You have to make a decision would you like assistance in troubleshooting an external power supply to a laptop? there is a logical process in the procedure itself, one must possess a command of electrical theory so let's cut the chit chat shall we?
 

Thread Starter

rambomhtri

Joined Nov 9, 2015
462
Guys, could it be that the blue LED is there to discharge the caps of the adapter once unplugged?

I didn't want to believe that because I remember almost 10 years ago, when I didn't know much about electricity and electronics, I disassembled one adapter one day just because I wanted to see what was inside a black box that said "Do not open", with my bare hands. Curiosity killed the cat, that time the cat was my finger flesh, and it was not killed, but gently shocked and very lightly burnt. Just a mark that is now long gone but that scared me to death, specially knowing it was not plugged in. That day I learned to take the labels more seriously and that when something is not plugged in does not mean it's safe, a thought that seems totally reasonable for most population that is completely ignorant about electricity and how it works.

Anyway, something really, really, really weird is happening. I was tired of trying different things and I decided to mesure things with the adapter plugged in, and covered with the plastic outer shells, removed just to take measurements with the probes and caring not to touch anything. I discovered one thing that blew my mind: the freaking output cable pins are at 19.5V. But then the cable end isn't. How is that even possible???

I measured the the cable continuity by putting one probe in the soldered joint and the other in the plug end. It beeped both times, so that means the black cable and white cable are not broken... How in heavens is this happening?
 

Thread Starter

rambomhtri

Joined Nov 9, 2015
462
Well, it appears to be so because I have measured the brown and blue caps with the adapter powered and they both read 300V DC, constantly. Then I unplugged and read about 250V and going down. I checked a few seconds, 200V. Then I waited the blue LED to be OFF and I measured 1.7V or so in both. So yeah, I do believe that the blue light is there to discharge the caps once unplugged.

Anyways, I unsoldered the output cable and I am getting continuity in both, although the inner +20V one cont. gets cut very often if I move around the cable. The weird thing is, I did this while tested the 20V DV output in the pins, I moved around the cable to check if I was able to get 20V sometimes. Nope, I was getting hundreds of mV always, never 20V, so that made me discard the fact that the output cables were broken (that and that both beeped in continuity).

Yes, intermittent contact in the inner positive output cable. The devil's work: it has not become intermittent until I have unsoldered it from the board. When it was soldered, I checked for cont. both wires, positive and negative, and also moved the cable around while doing it. Not a single intermittent beep, always constant beeps. So I guess in the end it's just a simple dead wire, so I am going to replace the output cable and post the results.
 

Thread Starter

rambomhtri

Joined Nov 9, 2015
462
Replace, I don't know where the problem is so better put everything new for a few bucks. I will report here the results, as I said. Thank everyone!
 
I've troubleshot a few laptop adapters and it was the cable. I bought a bunch with the 5.5/2.2 ends, I think. Including the ferrite.

The second problem is the power in. I replaced that on an Apple iBook. They made it a daughter card.

I had the DC in professionaly done. They puts the screws in the wrong place and cracked the case.

Right now, I'm partial to a grounded laptop adapter. I think it cuts down ESD issues.

I did fix an Amiga power supply.

I fixed about ten Sorenson DCR 300-3b or 0-300V 0-3A supplies. They all had the same age related problem and mybe one other problem. Excessive ripple. Had to change about 10 caps.

Most adapters full wave rectify 120 or half wave rectify 240 and you end up with around 300 VDC to start with.
Now the fun part, ground is offset by around 1.2V, so instruments go bang if they are grounded.

Most of the time, buy another because they are so cheap. Not worth reverse engineering and trying to fix because I don't have the time.

I have a console server that I bought off of ebay that doesn;t work. What I know:
5V supply is 4.75V and not rated for residential. If i were to replace it, a residential rated supply cost $3.00. Yes $3.00 New. The mounting holes won;t fit, but the plugs would. What would you do? Both supplies have OVP.

It doesn't work when I substituted a 5V 4A supply. No Ethernet activity lights. I checked the Ethernet transformers.
I replaced that in a DSL modem before.

It goes through the motions when you reset it. Lights blink correctly.

Considering it would cost about $1700.00 USD to replace new, another used one makes sense. Possibly a better model.

I want to connect to the console configuration port and I now have the cables to eventually do so. I want to know if the console interface works. What's odd is two parts that could be bad have an X through them. The transformer I could replace,

A lot of times power supplies for things end up on the surplus market. That happened with the Amiga PS and a PS for a CD burner.
 

Thread Starter

rambomhtri

Joined Nov 9, 2015
462
Guys that was it, it was the output cable, it was broken, yet somehow I got constant beeping when checked it, several times, moving and wrapping the cable and everything. Constant beep in both wires.

It was after I unsoldered the output cable that I re-checked for the 5th time for continuity and suddenly I got intermittent beeps in the +19.5V. I rechecked that 5th time after noticing that at the pins, with the adapter powered, I had 19.V... so it had to be the output cable, but that just was discarded after I tested 4 times the cable, and all the times it beeped just fine.

The devil's work! HAHAHA
 

Thread Starter

rambomhtri

Joined Nov 9, 2015
462
Probably the output circuit looked as a short to your meter.
How could it be shorted, first of all, without having some real problem in the adapter?
I mean, if they were somehow shorted in the middle, between the end plug and the soldered pins, surely something should have black smoked or stopped that, because the +19.5V were present all the time. How do these adapter protect against a short in the output plug?
Anyways, I discard a short also because I measured continuity between ground and positive, both ways, and didn't beep at all.

I lie there, actually, something really weird happened, but I thought was my problem or something minor like my DMM beeping because. If I placed a probe in the ground board pin and the other in the positive end of the plug, during the first half second it would beep. Then, no matter how much I twisted or moved the cable, it wouldn't beep. The fact that I twisted and moved the cable testing both continuity and short made me think that the cable was perfect. This is weird...
 
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