Testing laptop chargers

[joydivision]

I have a portable multimeter/scope which I bought second hand of a small loud speaker manufacture. It is great for measuring ripple on power supplies etc.

I have just collected a laptop from my DC jack repair place, the DC jack was loose and needed replacing but it still won't charge, my generic one doesn't fit.

I have tested the Lenovo charger with my scope and I get no output at all, however I assume with even with no load there needs to be some sort power so the charger can detect the load in the first place.

With a bit of wire wiggle I get a reading between 2.3v and 3v it up and down like a yoyo, so clearly this charger is faulty . Just tested my own Lenovo charger (sadly different tip) and get a solid reading of 20v. Feel a bit daft making this thread but has been one of them days where everything has gone wrong so I am going mad .

 

[Martyn]

Might be worth picking up one of these Ian? I've got two, one in the car and one in the workshop.

http://www.amazon.co.uk/gp/product/B009TNESKW?psc=1&redirect=true&ref_=oh_aui_search_detailpage

 

[joydivision]

I did have a couple of generic ones, but managed to blow them both up on the same bloody laptop! I was testing a DC jack first one I realised my generic was dead, so I tried my second one still dead! And by dead the chargers no longer worked on any other laptop and 0v output. Just not got round to getting a replacement but that one looks good.

Edit just ordered one Thanks Martyn.

 

[mraikes]

I have a portable multimeter/scope which I bought second hand of a small loud speaker manufacture. It is great for measuring ripple on power supplies etc.

I have just collected a laptop from my DC jack repair place, the DC jack was loose and needed replacing but it still won't charge, my generic one doesn't fit.

I have tested the Lenovo charger with my scope and I get no output at all, however I assume with even with no load there needs to be some sort power so the charger can detect the load in the first place.

With a bit of wire wiggle I get a reading between 2.3v and 3v it up and down like a yoyo, so clearly this charger is faulty . Just tested my own Lenovo charger (sadly different tip) and get a solid reading of 20v. Feel a bit daft making this thread but has been one of them days where everything has gone wrong so I am going mad .

I've never encountered a laptop charger that required load to measure it's voltage.

In most cases, if you can't measure roughly 19.5 volts at the tip, it's a bad supply. Look at the markings on the charger itself to see the exact output.

EDIT: Deleted comment about generic power supply, because OP already addressed it.

 

[Boston Pro Comp Serv LLC]

Correct they do not need a load to read voltage. If it wasn't supplying any juice until it was under a load how would it know there was a load? Which came first the chicken or the egg?

 

[mr m]

Laptop adapters are switching power supplies just like the PSU in a PC. The DVM acts like a resistor which is enough to load the adapter while a PSU needs a larger load like a hard drive or two to read the DC output.

 

[Larry Sabo]

Laptop adapters are switching power supplies just like the PSU in a PC. The DVM acts like a resistor which is enough to load the adapter while ...

I haven't looked at their internals but I'd be surprised if they were a switching PSU. I just assumed they were filtered and regulated (voltage and current). As for the DVM presenting a load, it does, but with an impedance of 1Megohm or more it isn't going to present a meaningful load to the AC adapter.

Edit: You're right! I learn something new every day on Technibble. Here's a circuit diagram: http://circuit-diagram.hqew.net/60-Watt-Laptop-Battery-Charger_11676.html

 

[Moltuae]

I haven't looked at their internals but I'd be surprised if they were a switching PSU.

I've stripped and repaired a few over the years. Most, if not all, are Switched-Mode.

They have to be really. At the kind of wattage most laptops require, an analog supply would have to be much larger and it'd dissipate a lot of heat.

 

[mr m]

I'm pretty sure laptop adapters are now switched-mode as opposed to linear but honestly I've never opened one up either.

Agree that a DVM doesn't provide a substantial load but it's enough to directly measure the DC Volts of an adapter unlike a PSU.

I started chip chasing almost 40 years ago when a computer tech had to understand electronics but haven't picked up a scope since the 80's. I miss those days and have long since lost those skills. I'm a hardware guy stuck in a software world.

 

[mr m]

I've stripped and repaired a few over the years. Most, if not all, are Switched-Mode.

Thanks for clearing that up. It took me 10 minutes to type a reply to Larry. After all these years I'm still using two fingers.

 

[mr m]

See, I left out a slash because I can't type!

 

[Moltuae]

Thanks for clearing that up. It took me 10 minutes to type a reply to Larry. After all these years I'm still using two fingers.

lol

My typing's not much better to be honest. Whenever I'm working in an office next to trillion-words-a-minute office staff, I have to pretend the reason I'm typing slowly is because I'm thinking.