Toshiba laptop charger power supply problems

[SuperAman]

I have a laptop charger that is not working. I have tested it and the capacitor is storing high voltages around 600v. Both transistors are reading ok as well as all the diodes including the bridge diode. I replaced the C139 cap on output mosfet (it was cracked). All the resistors test ok in circuit. Am I missing something? D32 has a partial short reading in circuit but with one pad removed it has correct diode readings. The model of the board is adp-45fe bb.

[SuperAman]

Re: Toshiba laptop charger power supply problems

[Askic]

Re: Toshiba laptop charger power supply problems

So, are you saying that this big capacitor 82 uF, 420V has 600V??? This doesn't sound right.

[SuperAman]

Re: Toshiba laptop charger power supply problems

So, are you saying that this big capacitor 82 uF, 420V has 600V??? This doesn't sound right.

I am saying it is storing voltage, it is not going to the secondary or output side. I am measuring in AC so that might be why the number is high. Whatever the case, the cap stores voltage and when I use a lightbulb (serial bulb circuit) to test, it shows no short. However, if I don't discharge the cap with my meter and I touch the board cap area, I am shocked very badly.

[petehall347]

Re: Toshiba laptop charger power supply problems

if I don't discharge the cap with my meter and I touch the board cap area, I am shocked very badly.

are you for real ?

[madan1]

Re: Toshiba laptop charger power supply problems

Remove all the white gunk from the board and post some nice clean photos.
Also, the most left cap ( c102? ) on the secondary side looks like a goner to me. Oh, and keep in mind that shocking yourself with a capacitor is not always the best way to check if it is ok or not.

[SuperAman]

Re: Toshiba laptop charger power supply problems

Remove all the white gunk from the board and post some nice clean photos.
Also, the most left cap ( c102? ) on the secondary side looks like a goner to me. Oh, and keep in mind that shocking yourself with a capacitor is not always the best way to check if it is ok or not.

Ok will do. I accidently shocked myself, since it didn't show a short on the light bulb test, assumed it was ok. I am discharging the cap with my multimeter now after each time the charger has been plugged in.

[petehall347]

Re: Toshiba laptop charger power supply problems

what multi-meter do you have ? i want one that does that

[sam_sam_sam]

Re: Toshiba laptop charger power supply problems

I am thinking that this person is just seeing the capacitor slowly discharging

Because I also seem this myself

[noizemaker]

Re: Toshiba laptop charger power supply problems

Speaking of notebook chargers, is it safe to remove Y cap from my Notebook charger (Lenovo Ideapad)? there is only one. I think it's connected to neutral-ground to filter EMI
However I'm using a surge suppressor with 2 Y caps
The Y cap in question on the charger is ce472m STE Y2 4700pF (quite high right?)

[noizemaker]

Re: Toshiba laptop charger power supply problems

what could other benefit of a Y cap like 4700pF have on a Notebook charger?

[Per Hansson]

Re: Toshiba laptop charger power supply problems

what multi-meter do you have ? i want one that does that

I am thinking that this person is just seeing the capacitor slowly discharging

Because I also seem this myself

Some multimeters have a low impedance mode, with a 3K series resistor instead of 10M.
Those can be quite useful to discharge capacitors unless the capacitor is really large.
(If it is then the PTC's inside the meter will heat up and the resistance increases so they discharge much slower).
Some more details here: https://www.badcaps.net/forum/showth...076#post886076

[stj]

Re: Toshiba laptop charger power supply problems

what multi-meter do you have ? i want one that does that

they all do that - once!
well maybe the 20A ones could do it a few times atleast - the cap can only hold a couple of amps if your lucky.

[momaka]

Re: Toshiba laptop charger power supply problems

I am measuring in AC so that might be why the number is high.

Electrolytic caps can only store a DC charge. Therefore, you should measure the DC voltage on that cap.
.
.
Not that I think this would reveal anything about the issue at this point.

However, if I don't discharge the cap with my meter and I touch the board cap area, I am shocked very badly.

I have a 15 KOhm, 5-Watt resistor for that purpose. When working on adapters like that, I always put this resistor across the main cap(s) - it discharges them in seconds. If the expected voltage is less than 320-340V, sometimes, I use my 4.7 KOhm 5-Watt resistor - really just a matter of whichever one I find first, most of the time.

Remove all the white gunk from the board and post some nice clean photos.

+1

Also, the most left cap ( c102? ) on the secondary side looks like a goner to me.

I doubt it. It appears to be United Chemicon brand. Unlikely to be bad, even in hot adapters like these.

Since the mains cap stays charged, I'm leaning more towards shorted output wires. Some PWM chips have crowbar protection and will latch down / stop all switching on primary until adapter is unplugged. So that's how the primary cap can stay charged for a long time.

Speaking of notebook chargers, is it safe to remove Y cap from my Notebook charger (Lenovo Ideapad)? there is only one. I think it's connected to neutral-ground to filter EMI

It's not unsafe.
But it's not recommended, though, for EMI/RFI suppression purposes, as you noted.
Also, it isn't necessarily connected Neutral to ground. If the Y-cap is near the switching transformer and connected between ground on the secondary and some part on the primary, that part is probably the negative (-) lead of the bulk cap.

are you for real ?

Why not?

I've done it a few times too (a couple on purpose too.) It's not dangerous as long as the discharge path is only through parts on one hand. Now if you discharge such cap across your body, that would be a lot more painful and dangerous.

well maybe the 20A ones could do it a few times atleast - the cap can only hold a couple of amps if your lucky.

??
I think you meant to say Joules of energy instead of Amps?

[stj]

Re: Toshiba laptop charger power supply problems

no, the ripple current of the cop relates to it's discharge rate.

[madan1]

Re: Toshiba laptop charger power supply problems

...
I doubt it. It appears to be United Chemicon brand. Unlikely to be bad, even in hot adapters like these.
...
Since the mains cap stays charged, I'm leaning more towards shorted output wires. Some PWM chips have crowbar protection and will latch down / stop all switching on primary until adapter is unplugged. So that's how the primary cap can stay charged for a long time.
...

About the cap - on the photo it looks like starting to bulge, but could be just the light.

I have two acer PSUs ( one for laptop, the other for a portable pc ).. both work fine, both are visually the same, have the same output V, but probably the PC one was a little bit more powerful ( if I remember correctly ).. anyway - the laptop one has a discharge resistor for the main cap, the other one - does not and keeps charge for hours even days after disconnected from the mains.

[stj]

Re: Toshiba laptop charger power supply problems

sounds simple, but check the output cable isnt broken or shorted internally.

[noizemaker]

Re: Toshiba laptop charger power supply problems

It's not unsafe.
But it's not recommended, though, for EMI/RFI suppression purposes, as you noted.
Also, it isn't necessarily connected Neutral to ground. If the Y-cap is near the switching transformer and connected between ground on the secondary and some part on the primary, that part is probably the negative (-) lead of the bulk cap.

why such high value for a Y cap in a notebook charger? besides shouldn't them come in pair?
4700pf would cause more noise in the neutral or ground than no Y cap at all. Let's assume this cap is connected between line and ground... this is ultra unsafe

[momaka]

Re: Toshiba laptop charger power supply problems

why such high value for a Y cap in a notebook charger? besides shouldn't them come in pair?

If you do see a pair of Y2-class caps, they are connected Live-to-Ground and Neutral-to-Ground... or like so:

[Live]--------||-------[Ground]-------||--------[Neutral]

But in cheaper/smaller power adapters, it's also not uncommon to not have the two Y2 class caps mentioned above and instead have only one Y2 cap between negative (-) primary bus (the negative of the primary cap) and ground / secondary-side ground/return.

4700pf would cause more noise in the neutral or ground than no Y cap at all.

Beyond my knowledge to explain exactly, but bigger cap shunts more of the high-frequency noise to ground, so Live and Neutral stay "cleaner", which means other devices connected to the same Live and Neutral will also see less EMI/RFI noise.

Let's assume this cap is connected between line and ground... this is ultra unsafe

It's not if the cap is certified Y2 (or Y4) by safety agencies - meaning, it should go open-circuit in case it fails for whatever reason.

[SuperAman]

Re: Toshiba laptop charger power supply problems

I've tested nearly everything on this and it is either a bad ic31 chip or the small smd resistors feeding into it. Or a bad ic131 on the output side, I don't have these ic or resistors in my junk collection so have abandoned the repair.