Charging slowly

[starLED]

My phone is having problems with charging.
Its 2 years old phone.
When the battery is 50% charged I plug in charging connector and it shows that it takes about 4 h and 30 min to fully charge.
I take the plug out and plug it in again and then it shows 2 h and 30 min to fully charge.
Sometimes I need to repeat this couple of times to charge fast(er).
I tried the brand new charger adapter and it always takes about 1 h and 30 min to fully charge from 50% to 100%.
So, I measured the voltages in old and new charger adapter, and old one measured 4.84 V and new one 4.96 V.
Can this difference in voltages cause the charging slowly?

 

[Nigel Goodwin]

Measuring the off load voltage is telling you nothing, as the old adaptor doesn't work, and the new one does, then the old one is faulty. It 'might' be something as a simple as high ESR capacitors in the charger.

 

[starLED]

Can this be repaired?
Is it worth to open the adapter and diagnose?

 

[Nigel Goodwin]

Can this be repaired?
Is it worth to open the adapter and diagnose?

Yes, see post #2

 

[starLED]

I have disassembled the charger.
I am not sure if the blue 400V capacitor has a little bulge on the top.

 

[Nigel Goodwin]

I wouldn't say there's a bulge, but only some faulty capacitors bulge - I take it you don't have an ESR meter?. If the blue one is 400V,then it's the main reservoir, and those kind of capacitors don't ESR terribly well anyway, even good ones have fairly high ESR (compared to lower voltage caps).

Does your multimeter measure capacitance?, if so try taking the capacitors out of circuit, and testing them with that. The blue one certainly could cause the problem you're having, but so could the others - for C7 and C8, BOTH would have to be faulty.

It seems a pretty crappy charger, as there's no feedback between secondary and primary.

 

[starLED]

Yes, I can measure capacitance with my multimeter.

Phone in question is NOA VIVO 4G, it's a basically chinese 80$ phone, so charger is of course pretty crappy, but I am very satisfied with the phone, and I would like to fix the charger anyway.
If caps are the only problem, then replacing them is fairly cheap.

What is the blue component marked with CY1 at the top of the PCB?

 

[starLED]

I can't measure capacitance of C7 and C8, they are both 330 μF, my multimeter can measure only up to 200 μF.

 

[Nigel Goodwin]

What is the blue component marked with CY1 at the top of the PCB?

It's a special safety capacitor across the primary (live) and secondary (isolated) sides of the transformer - they don't really ever fail.

 

[Nigel Goodwin]

I can't measure capacitance of C7 and C8, they are both 330 μF, my multimeter can measure only up to 200 μF.

Check them anyway - if they are low, they are probably going to be lower than 200uF, and if they read over range are almost certainly OK.

 

[starLED]

I desoldered caps and measured them, here are the values:
C1 3.3 uF 400V = 2.3 uF
C2 6.8 uF 400V = 6.5 uF
C3 4.7 uF 50V = 3.5 uF
C7 330 uF 6.3V = above 200 uF
C8 330 uF 6.3V = above 200 uF

 

[Nigel Goodwin]

C1 and C2 in particular look a bit low, which 'could' signify they are high ESR, possibly C2 as well?, but that's not far off.

I don't suppose you have access to a scope?.

You could always try blanket replacing all five capacitors, but is it worth it?.

 

[starLED]

I could replace C1, C2 and C3, I think they cost less then 1$ all together.
I don't have a scope.