EEVblog Electronics Community Forum

Electronics => Repair => Topic started by: Bondguy on November 16, 2016, 09:21:18 pm

Title: Asus Transformer TF300
Post by: Bondguy on November 16, 2016, 09:21:18 pm
I have Asus Transformer TF300 tablet where digitizer( touch screen)  does not work. More digitizers were tested yet none worked.
So I guess it is a problem on mainboard. The digitizer does not have any Touch Controller on its flat cable so I think there must be one on the tablet mainboard. That touch controller can be faulty but also paths to the digitizer or there can be any other  reason why the touch screen does not work.
Can anyone suggest a procedure how to try to repair that problem? Thank you for your advice.
Title: Re: Asus Transformer TF300
Post by: singapol on November 17, 2016, 01:51:07 am
Check the power supply? But I suspect some smd electrolytic capacitors may have higher esr.Do you have esr meter  to check in-circuit?
Title: Re: Asus Transformer TF300
Post by: stj on November 17, 2016, 02:20:17 pm
i had this on a TF103, reflow the controller i.c.

can you post a foto with the rear cover removed?
Title: Re: Asus Transformer TF300
Post by: wraper on November 17, 2016, 02:32:55 pm
Quote from: singapol on November 17, 2016, 01:51:07 am
But I suspect some smd electrolytic capacitors may have higher esr.Do you have esr meter  to check in-circuit?
except there is none.
Title: Re: Asus Transformer TF300
Post by: wraper on November 17, 2016, 02:38:42 pm
Quote from: stj on November 17, 2016, 02:20:17 pm
i had this on a TF103, reflow the controller i.c.

can you post a foto with the rear cover removed?
yep, if there are no signs of corrosion, likely you would need either replace or reball touch countroller IC. In small portable deices it is not uncommon solder balls coming off on mechanical impact. you could try pressing on it (starting doing so before powering on) and see if touchscreen starts to work.
Title: Re: Asus Transformer TF300
Post by: stj on November 17, 2016, 04:48:50 pm
no need to replace or reball, just put flux under it and re-flow it.

it's a "flip-chip" package, and on the T103 is on a sub-board.
Title: Re: Asus Transformer TF300
Post by: wraper on November 17, 2016, 04:55:02 pm
Quote from: stj on November 17, 2016, 04:48:50 pm
no need to replace or reball, just put flux under it and re-flow it.

it's a "flip-chip" package, and on the T103 is on a sub-board.
Usually this does not help to make a solder joint again, as pad needs to be retinned before solder sticks to it again. Also IC may be underfilled.
Title: Re: Asus Transformer TF300
Post by: stj on November 17, 2016, 05:19:49 pm
your talking theory's to somebody who has already done it.
there is no underfill on these, and no oxide issues - just cracked solder joints probably caused by flexing of the pcb with a long and thin chip on it.
Title: Re: Asus Transformer TF300
Post by: wraper on November 17, 2016, 06:00:52 pm
Quote from: stj on November 17, 2016, 05:19:49 pm
your talking theory's to somebody who has already done it.
there is no underfill on these, and no oxide issues - just cracked solder joints probably caused by flexing of the pcb with a long and thin chip on it.
You are talking with one who professionally repaired mobile phones for many years. The thing is, you are left with bare oxidized copper on one side and solder ball on other.
Title: Re: Asus Transformer TF300
Post by: stj on November 17, 2016, 07:07:14 pm
it's not a fone - the chip is not that small.
Title: Re: Asus Transformer TF300
Post by: Rasz on November 19, 2016, 05:04:57 pm
you are both correct :)
reflow, then reball if still broken