Apple Magsafe

[LoboX]

Sup all i am new to this forum, i have no knowledge whatsoever regarding electronics, i am more IT, but a friend of my that has $$$$ issues cant buy a new adapter so i am trying to see if i can fix his broken adapter.

I have been seeing YouTube and tutorials to learn about AC/DC and how to use a multimeter, i have learn quiet something cause i knew nothing.

1 question if a Power Adapter Magsafe or any other, is not giving you the correct output volt like 16.5v and is giving you 0.56 what could be the problem inside the board.

Any tips would be great.

Thanks

 

[(*steve*)]

Beware, because even after they've been turned off these devices can store a high voltage charge that will make you wish you'd never been born if you come into contact with it. If you're really unlucky it could kill you. With the power connected they can be lethal.

Having delivered the warning...

I would say it's borked.

Opening it up and showing us pictures of both sides of the board would be helpful.

Possibly more helpful would be for you to sniff around and see if you can locate an area of the board with any acrid smell. You may also see smoke residue on the inside of the case.

If you want to go further, take some sharp clear photos of both sides of the board with indirect light (outdoors, shade, NOT flash), Ensure we can read what is written on the components.

 

[techiesteve]

The Magsafe Power Adapter was never meant to be serviced, so is unfriendly to work on. For user safety the casing is glued together. To gain access you would have to carefully use a dremel to cut along the joins. It wouldn't surpass me if they suffered from electrolytics with high ESR as they run very hot with no ventilation holes. Many Apple Time Capsules suffer like this. I'm experienced in sm psu repair, but would never waste my time opening up a magsafe adapter. I find a great many that fail are due to the dc cable being stressed. Every now and then I'll make one out of two by grafting a good cable to a good power adapter, but would only use within our workshop.

Bear in mind that the output voltage of a good power adapter is a lot lower than normal under no load, but the voltage you measured indicates a fault.

Steve

 

[KrisBlueNZ]

Bear in mind that the output voltage of a good power adapter is a lot lower than normal under no load [...]

I'm interested in that comment. Is that because the adapter hiccups due to output overvoltage with no load, so the average output voltage you measure is lower than the specified voltage?

 

[davenn]

..........Bear in mind that the output voltage of a good power adapter is a lot lower than normal under no load, but the voltage you measured indicates a fault.

Steve

Never the case in dozens and dozens of PSU's I have worked on over the years

I would deem that a very off the mark comment and bad advice

Regulated PSU's will show the correct voltage with or without a load
Unregulated PSU's will normally show a Voltage several Volts higher when there is no load and will come down to their stated Voltage once load is applied

Dave

 

[techiesteve]

Never the case in dozens and dozens of PSU's I have worked on over the years

I would deem that a very off the mark comment and bad advice

Regulated PSU's will show the correct voltage with or without a load
Unregulated PSU's will normally show a Voltage several Volts higher when there is no load and will come down to their stated Voltage once load is applied

Dave

Dave, I would agree with your comment with reference to power supplies other than the 60W and 85W Apple Magsafe power adapters, to which my comments were addressed.

I've just measured the output of an 85W unit off load, it reads 6.67V with a DVM. The spec is 16.5 - 18.5V output. I understand where you are coming from, but this is not bad advice, as without knowing this a good power adapter could be condemned as bad.

KrisBlueNZ makes an interesting point in another post. If the output was rising, crowbaring, then rising again in a repetitive way, a DVM sampling at a slow rate would indicate a lower average output voltage. If that was happening, I would still expect a little fluctuation in the DVM reading, but the output is steady, only wandering a little by 0.01V. I don't have a chance to scope the power adapters output until the weekend.

I'm not offering an explanation as to why the off load voltage is low, but am describing accurately what is happening to the off load voltage of a good Apple Magsafe power adapter.


Steve

 

[(*steve*)]

I've seen small SMPS power supplies that seem to exhibit this type of behaviour. (typically ex-phone charger type plugpacks.

I've never really known if they were that way by design or if due to a fault.

I've never actually looked at the output waveform on my scope either.

I'll pay more attention next time I come across one.

 

[KrisBlueNZ]

I wasn't actually suggesting any crowbar action, although that's possible as well. I was thinking that when the control IC has already reduced its output duty cycle below some minimum value, and the voltage feedback circuit is still telling it that the output voltage is too high, the control IC could regard this as an overvoltage (or under-loaded) condition, and trip on output overvoltage. It would then soft-start and the cycle would repeat.

Another possiblity would be that the control IC is designed to detect an unloaded output condition (again, by detecting that its operating duty cycle is low but the output voltage is not), and enter a low-power mode in which it "drip-feeds" the switching transformer just enough energy to provide a minimal output voltage so that it can detect connection of a load and switch to normal operating mode.

This would greatly reduce the standby current for circuits such as chargers, which are often left plugged in when not in use. This might be required for "green" compliance in some countries.

 

[techiesteve]

Yesterday I stripped the case off an Apple 60W Magsafe power adapter. This is likely a worker, but the DC cable had broken right up to the 'protective' cable gland. This gives an idea of what's inside the white case. On the PCB top side there are also smd devices, including at least one IC, hidden away under larger components. After cracking the case open I also had to remove metal RF shielding that encapsulated the PSU.

Steve

 

[KrisBlueNZ]

They really like to pack it in there, don't they. I was looking at a 90W supply for a friend. It's enclosed in a plastic case about 100 x 100 x 30 mm. There's a metal screen around the board, then some crusty stuff in there, presumably to improve heat conduction to the plastic case. He says it gets quite warm.

Unfortunately this one wasn't repairable. The inductor (actually it has a secondary winding as well) in the power factor correction circuit was open circuit; probably, the adapter was dropped and the force due to the mass of the transformer core pulled one of the bobbin pins out of its plastic, breaking the main winding.

 

[LoboX]

Thank you for all your replies, What i did was i took it to another person who knows electronics and he was able to fix it, I need to take a basic course of electronics to do this kinds of things. But thank you for the replies guys.