My tablet charger burnt! Why? - Page 1
Forum section: electronics / beginners

author: rozeh
author_rank: Regular Contributor
timestamp: December 15, 2013, 08:45:18 am
content: Hi everybodyI have a chinese tablet. yesterday, when I plugged it in for charching, after 5-10 minute, it burst!(BoOoOoM!!!!). I opened itand saw in it. I can say to you that it fried!!!! anfter probing, I found that the fuse in it has burst. look:if you look at the back of PCB, You will know that the part of 220v was tooooo much hot! look:some part of PCB has destroyed. for example look this picture:Now questions:1- What is really the problem of circuit?(in other word, Why it burnt?)2- What type Fuse I should put instead burned out fuse?3- How can I repair that part of PCB that destroyed?

author: tszaboo
author_rank: Super Contributor
timestamp: December 15, 2013, 09:15:17 am
content: It died, because it is Chinese. As far as I can see, there is a place for a MOV, which is not there. Also, the whole input protections is one fuse, not to mention there is no inrush current protection. You are better if you buy a brand charger like Belkin or Hama.

author: IanB
author_rank: Super Contributor
timestamp: December 15, 2013, 09:16:18 am
content: I don't think you can even try to repair that. It is toast.Determine its electrical specifications and then get new one to replace it.

author: SeanB
author_rank: Super Contributor
timestamp: December 15, 2013, 09:20:17 am
content: With that bang at least you will find all 4 diodes in the bridge are either open or short curcuit ( I would lean to 2 being short at least but change all 4)and the winrise switcher being cooked and short. Resistor under the heatshrink is a fusible resistor, probably around 10R 0,5W. Replace with another fusible resistor or a series 10R 1W resistor and a 1A fuse. I would suspect all the electrolytic capacitors on the primary side and C3 as well as being either high ESR or short or open. The SMT resistors as well need checking, especially the low value ones, as they are likely to have been blown open.Best bet though is to buy another 2A clone charger or two and use them until they pop.

author: rozeh
author_rank: Regular Contributor
timestamp: December 15, 2013, 09:21:43 am
content: OK,It is 5v 2A. Thanks guys. I get a adaptor with this characteristics.

author: rozeh
author_rank: Regular Contributor
timestamp: December 15, 2013, 09:26:48 am
content: Guys, What will happen if I use a 3A or 1A instead a 2A?

author: SeanB
author_rank: Super Contributor
timestamp: December 15, 2013, 09:44:01 am
content: 1A will take longer to charge if it will charge at all, and a 3A unit will be fine. The common chargers are very optimistic in the ratings ( those that lie totally about the ratings are another case) and often cannot supply full rated current at rated voltage, like the one you have which was overloaded. Buy a 3A one of better quality.

author: peter.mitchell
author_rank: Super Contributor
timestamp: December 15, 2013, 09:46:25 am
content: 3a vs 2a = will do the same as each other, may charge slightly faster on 3a charger, if existing 2a charger was shit (hint: it was)1a vs 2a = will charge slowly, or won't charge at all - if it is a cheap 1a charger, it may even damage the device due to massive ripple.

author: rozeh
author_rank: Regular Contributor
timestamp: December 15, 2013, 09:53:00 am
content: Quote from: SeanB on December 15, 2013, 09:44:01 amThanks SeanBut I heared If we use of a bigger charger(for Current not voltage), The battery will be destroy very soon.Quote from: peter.mitchell on December 15, 2013, 09:46:25 amOk, then I want to buy a 3A charger.

author: peter.mitchell
author_rank: Super Contributor
timestamp: December 15, 2013, 09:56:48 am
content: Quote from: rozeh on December 15, 2013, 09:53:00 amThis MAY be the case if it was a charger, but it wasn't, it was a power supply, for the charger and tablet. The actual charger is inside the tablet, the external unit just powers the charger.

author: rozeh
author_rank: Regular Contributor
timestamp: December 15, 2013, 10:09:18 am
content: Quote from: peter.mitchell on December 15, 2013, 09:56:48 amGreat! thank you, peter

author: tszaboo
author_rank: Super Contributor
timestamp: December 15, 2013, 10:16:20 am
content: Quote from: rozeh on December 15, 2013, 09:26:48 amWell my nexus 7 goes crazy (touchscreen) if I connect a charger with less current.

author: amyk
author_rank: Super Contributor
timestamp: December 15, 2013, 12:38:33 pm
content: That's actually rather high-end construction for a device like this... fused, $$$ controller IC (which isapparently within 1 feet of a start capacitor), routed isolation on the HV side, lots of clearance, safety rated EMI reduction cap, SMD parts on the bottom, etc. I'm guessing a power surge killed it.

author: minime72706
author_rank: Frequent Contributor
timestamp: December 15, 2013, 04:39:52 pm
content: That is a truly impressive electrical failure! The fuse basically disappeared!BTW it's not the lowest-quality charger I've seen, but it's still pretty bad. The only thing it has going for it is that it has a legitimate control IC.

author: peter.mitchell
author_rank: Super Contributor
timestamp: December 15, 2013, 08:32:55 pm
content: Quote from: NANDBlog on December 15, 2013, 10:16:20 amYeah, there are a few reasons for that, one may be an insufficient connection to ground on the charger, or excessively high ripple coupling to the touchscreen.

author: Retep
author_rank: Regular Contributor
timestamp: December 15, 2013, 10:19:38 pm
content: Quote from: minime72706 on December 15, 2013, 04:39:52 pmAnd a fuse...which more than what one should expect to find in a Chinese turd.

author: minime72706
author_rank: Frequent Contributor
timestamp: December 15, 2013, 11:16:56 pm
content: Quote from: Retep on December 15, 2013, 10:19:38 pmIndeed ... one of the many switchers I have taken apart for fun used a low-value 1/4 watt carbon-film resistor as a fuse ...

author: codeboy2k
author_rank: Super Contributor
timestamp: December 16, 2013, 01:33:22 am
content: The sad thing is that they actually used decent parts, as has been pointed out, and it was killed by a surge that might have been prevented if they had only populated the MOV.Chances are they don't care, because blown parts means most people will buy a new one, and that means more sales for them.I am sure they think like this because they don't yet have the gamut of consumer protections that most western countries have.

author: minime72706
author_rank: Frequent Contributor
timestamp: December 16, 2013, 02:44:28 am
content: Quote from: codeboy2k on December 16, 2013, 01:33:22 amThey used decent parts, but the design is still bare-bones. MOV ... inrush thermistor ... external switching device, etc.WHERE'S MY TL431, HUH?

author: M0BSW
author_rank: Frequent Contributor
timestamp: December 16, 2013, 07:56:43 am
content: probably a cheap wun hung low job, they had a tv program on them over here, when people bought the cheap and nasty thing as replacement for the mobile phones, some blew up on first switch on, the fire brigade was saying, they'd attended some house fires because of them,scary

author: minime72706
author_rank: Frequent Contributor
timestamp: December 16, 2013, 03:18:51 pm
content: I doubt that the charger would have survived the surge even with the 7-10mm MOV that could have been installed in it, if that's any consolation. At least your tablet is safe?Go make your ownGet a CUI or similar AC/DC module and cover the thing in surge protectionExample: CUI part number VSK-S10-5UAMOVs and TVS diodes are not expensive! I have boatloads.

author: toxicnos
author_rank: Contributor
timestamp: December 16, 2013, 10:58:47 pm
content: Don't even bother repairing it man, it's completley destroyed. You 're better off buying a wall wart with the same voltage and amps and soldering the connector to it.