Help needed identifying SMD component - Page 1
Forum section: electronics / repair

author: TurboTom
author_rank: Super Contributor
timestamp: December 06, 2015, 04:59:05 pm
content: I'm about to repair a Medion S9714 tablet pc which was showing strange battery drain even if shut down completely, a lot of heat dissipation when working or charging and the backlight not reaching full brightness.I narrowed the problem down to a tiny boost converter that's always getting quite hot, even if the tablet is shut down and the backlight / TFT is off. I guess the converter chip itself is faulty, maybe as the result of a defective inductor (will have to check that). The problem is, the semiconductor is enclosed in a tiny DFN-8 package (2*2mm² footprint) that only carries the designation "7212" and in the second line "8". I attached a few pictures with a photo of the corresponding PCB section, a schematic (as transscribed from the PCB) and two thermal images of the section and the complete board with only the battery plugged in an nothing else started/energized - clearly observable, the only heat source is the mentioned chip (some apparent heat sources are reflections on the RF shielding cans). Has anybody got a clue what semiconductor this is? I tried comparing the major manufacturers' stuff but didn't find a matching pinout so far. Thanks for the help!Cheers,Thomas

author: orbiter
author_rank: Frequent Contributor
timestamp: December 06, 2015, 05:20:47 pm
content: SMD cross reference shows it as perhaps a step up converter and spits back the reference APW7212.Here's a link to the .PDFhttps://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwj4nJa43sfJAhVB0BoKHff4AZwQFgggMAA&url=http%3A%2F%2Fwww.anpec.com.tw%2Fashx_prod_file.ashx%3Fprod_id%3D338%26file_path%3D20110315171611560.pdf%26original_name%3DAPW7212.pdf&usg=AFQjCNG_GBQRmsHpRuOnTGNPzGSWPLke3w&sig2=r8n81cJJKtBzbkhHCHHwoA&cad=rja

author: TurboTom
author_rank: Super Contributor
timestamp: December 06, 2015, 05:35:48 pm
content: Orbiter -thanks a lot, that's a great help! Indeed I never heard of the company "Anpec" and probably would have continued to search the web for ages to find the component -- if I had succeeded at all ;-).I'll drop a line here if I was able to source the spare and if the repair job was successful.Thanks again and all the best,Thomas

author: wraper
author_rank: Unknown
timestamp: December 06, 2015, 08:15:23 pm
content: Quote from: TurboTom on December 06, 2015, 05:35:48 pmSeems like aliexpress and taobao are the only sources to get this.http://www.aliexpress.com/item/APW7212QBI-TRG-ANPEC-DFN8-original-5PCS/32306413238.html?spm=2114.01020208.3.1.iZMAq3&ws_ab_test=searchweb201556_1_79_78_77_80,searchweb201644_0,searchweb201560_10http://world.taobao.com/item/43299310566.htm?spm=a312a.7700714.0.0.E7J2zp#detail

author: Neilm
author_rank: Super Contributor
timestamp: December 07, 2015, 10:35:40 pm
content: That package has a pad on the underside. I have had occasions with converters running hot when this pad has not been properly soldered. As this pad is used as a heat sink as well as the 0V connection you can have it sort of working but not performing correctly. Try reflowing it before replacing it.

author: TurboTom
author_rank: Super Contributor
timestamp: December 08, 2015, 08:47:47 am
content: Neilm -thanks for the hint - yet, the shutdown pin is low and the chip is getting hot nevertheless. This makes me conclude it went bananas. Since the board had been professionally assembled and the soldering quality looks rather good, I think there's no reason to assume the exposed pad isn't soldered on correctly. Of course I'll have to take care of that when I insert the replacement chip. Fortunately, I've got the required equipment available at work.Wraper - thanks for the link!Cheers,Thomas