Sony Ericsson CST-60 Charger

[TimeManx]

Hi guys, an SE CST-60 charger doesn't work anymore after the wires going into the pins (not from the mains) touched each other.

I did google for a CST-60 circuit diagram but couldn't find one.

There might have certainly been a safety measure implemented to protect the whole circuit. I'm a total newbie in this but still I'm guessing maybe it's the diode which directly gets connected to the mains.

Opinion from others is greatly required.

 

[Tesla]

Look for a blown fuse or diode.

 

[TimeManx]

Look for a blown fuse or diode.

No fuse but a diode is connected to the main & another one with the transformer.
And how would I know what diode to replace with.

 

[Tesla]

Is this a cell phone A/C desk charger or a car charger?

Diodes should first be checked with a DMM to determine if they are bad or not before trying to replace them.

 

[Tesla]

It's an AC wall-wart charger.

Unless it's an easy obvious fix, I wouldn't risk fixing it. If it's repaired improperly, it might be a fire hazard or damage the phone.

You can get a new one at Buy.com or amazon for about $6 shipped to your door.

I don't think you can beat $6 for a brand new one, but RadioShack (AT&T dealer) or an AT&T store might have some used ones laying around, that used to be paired with now un-repairable phones.

 

[TimeManx]

It's an AC wall-wart charger.

Unless it's an easy obvious fix, I wouldn't risk fixing it. If it's repaired improperly, it might be a fire hazard or damage the phone.

You can get a new one at Buy.com or amazon for about $6 shipped to your door.

I don't think you can beat $6 for a brand new one, but RadioShack (AT&T dealer) or an AT&T store might have some used ones laying around, that used to be paired with now un-repairable phones.

Yea you're right. But if it can be fixed easily then why not.
There's a zener diode at the circuit out. You think that can be the problem.

 

[Tesla]

Yea you're right. But if it can be fixed easily then why not.
There's a zener diode at the circuit out. You think that can be the problem.

Possibly ... do you know how to remove it from the circuit and check it?

If it's right near the DC output, it's probably there to keep the cell phone's battery from discharging into the adapter itself (keep the power going in one direction ... INTO the battery).

The trick to cross referencing a zener diode is you have to know the voltage spec. on it and the wattage it needs to handle. As you probably know, there are also plain diodes and even other special kinds.

Also, after you attempt to fix it, I would check the power output with a DMM first (not the phone). I think it should be 5v DC.

And in general (unless you have an electronics supply house local to you) ... although the parts aren't expensive, with shipping and handling, it's hard to get them to your door-step for less than $5.

 

[TimeManx]

Possibly ... do you know how to remove it from the circuit and check it?

If it's right near the DC output, it's probably there to keep the cell phone's battery from discharging into the adapter itself (keep the power going in one direction ... INTO the battery).

The trick to cross referencing a zener diode is you have to know the voltage spec. on it and the wattage it needs to handle. As you probably know, there are also plain diodes and even other special kinds.

Also, after you attempt to fix it, I would check the power output with a DMM first (not the phone). I think it should be 5v DC.

And in general (unless you have an electronics supply house local to you) ... although the parts aren't expensive, with shipping and handling, it's hard to get them to your door-step for less than $5.

I have these markings on the zener diode
c3v9
5t
5 below 3 and t below v (the forum is wrapping out the spaces). What does that mean?
BTW Zener diodes can be tested the same way as a normal diode, can't they?

EDIT: After googling I found that it's a 3.9 V Zener. But what does 5t mean?

 

[Tesla]

I have these markings on the zener diode
c3v9
5t
5 below 3 and t below v (the forum is wrapping out the spaces). What does that mean?
EDIT: After googling I found that it's a 3.9 V Zener. But what does 5t mean?

It might be a 3.9v zener diode. Not sure about the wattage (might have to guess-timate from the physical size).

http://www.google.com/search?hl=en&source=hp&q=c3v9+diode&aq=f&aqi=&aql=&oq=&gs_rfai=

Does it check bad removed from the circuit?

 

[Tesla]

BTW Zener diodes can be tested the same way as a normal diode, can't they?

EDIT: After googling I found that it's a 3.9 V Zener. But what does 5t mean?

Yes, you check zeners the same way.

I think 5t is just a manufacture or lot code (you can ignore it).

 

[TimeManx]

It might be a 3.9v zener diode. Not sure about the wattage (might have to guess-timate from the physical size).

http://www.google.com/search?hl=en&source=hp&q=c3v9+diode&aq=f&aqi=&aql=&oq=&gs_rfai=

Does it check bad removed from the circuit?

The resistances are infinite on both checks. So I guess so.

 

[(*steve*)]

Zener diodes are almost always used as a shunt. The chance of damaging a zener by momentarily shorting the output is slim.

I would certainly not be focusing on it unless I had specific reason to believe it failed.

 

[TimeManx]

Zener diodes are almost always used as a shunt. The chance of damaging a zener by momentarily shorting the output is slim.

I would certainly not be focusing on it unless I had specific reason to believe it failed.

But it is possible, isn't it? And it is giving infinite both times so that does confirm it, doesn't it? I am confused.

 

[(*steve*)]

Sorry, I started replying before you posted that additional information.

If the zener is indeed dead, I would be worried about what else may be dead.

I'm assuming it's a linear power supply? (transformer and only a few additional components).

I would start by measuring the voltage on the secondary of the transformer (and I'd be *very* careful doing it as you'll likely be rather too close to whatever mains voltage you have). If the transformer is working, move forward until you see what's not working. If it's a simple linear supply, then it would be the pass element (transistor, mosfet, or possibly even a large resistor) that I would be looking at.

edit: The above assumes that nothing is getting hot or smoking

 

[Tesla]

Zener diodes are almost always used as a shunt. The chance of damaging a zener by momentarily shorting the output is slim.

I would certainly not be focusing on it unless I had specific reason to believe it failed.

Agreed, but he says it reads "open".

Can he not check for DC voltage just on the other side (input side) of the possibly bad diode? If the diode is open, and everything else is good, wouldn't he get some voltage?

I still say there should have been a pico-fuse in there. Remember, it might look like a diode or even a tiny box-like capacitor.

 

[TimeManx]

I still say there should have been a pico-fuse in there. Remember, it might look like a diode or even a tiny box-like capacitor.

There's a photocoupler, PC123.

EDIT: I don't know what a picofuse is but there is a green coloured thing which says 2A502K. I thought it was a capacitor.

 

[Tesla]

There's a photocoupler, PC123.

Ya, pretty amazing how sophisticated some of these wall-warts are these days. Back in the old days it was just a transformer .

The photocoupler is likely used in the feedback circuit (shuts the whole thing down when voltages don't look right).

EDIT: Another advantage is this one is eco-friendly. It only starts using a lot of power when there is a load on it.

 

[Tesla]

There's a photocoupler, PC123.

EDIT: I don't know what a picofuse is but there is a green coloured thing which says 2A502K. I thought it was a capacitor.

I could send some links if you want but basically it's a small part that will likely have a mA notation on it like a fuse does.

http://search.digikey.com/scripts/DkSearch/dksus.dll?vendor=0&keywords=507-1171-ND

Other look like a tiny round capacitor or even a diode.

 

[TimeManx]

Sorry guys. Turns out the zener diode is fine after all. It was my multimeter that was malfunctioning. Tried it with another one and it was fine.

Sorry, my bad. Back where started.

 

[(*steve*)]

OK, it's a switch-mode power supply.

These are very different beasts to repair than a simple linear PSU.

I would advise *not* running any tests with the power on, and I would also advise you to be very careful near capacitors that will probably be charged via rectified mains.

edit -- I told you I was surprised

edit again: the optocoupler is almost certainly involved in communicating between the low voltage side of the circuit and the high voltage (mains potential) and is almost certainly a feedback mechanism to ensure regulation.