Bongofish

Screen Tablet malarky => Heyaaaalpppp => Topic started by: Drewid on August 15, 2017, 07:07:37 PM



Title: Guess who :)
Post by: Drewid on August 15, 2017, 07:07:37 PM
Hello.

Long time no post and all that  ;D   

I have a similar problem to the guy in the,  dropped 21UX thread.
I've snagged myself a dirt cheap 21UX. It was cheap because a strip (about 2cm across the whole center of the screen) isn't picking the pen up. I figured it might be a loose ribbon cable but it doesn't look like that's it. (re-seated all the cables and no change)
This is the main board:
[attachment=1]

It's going to be one of these circuits in the middle

[attachment=2]

 I was hoping for an missing SMD or dry joint something but there isn't anything obvious that I can see.
I'm not really into electronics above the simple soldering and testing level but I'll give anything a go. 
I may have to try to get a replacement board from somewhere, perhaps a scrap one with a cracked screen or something.



 


Title: Re: Guess who :)
Post by: Ertew on August 16, 2017, 09:57:45 PM
Hi.

As You can (cannot) see, single broken solder joints cannot be fixed because You cannot see the problem.
If there are soldering problem I will try to locate what section are responsible for 2cm gap, then use hot air for resolder many components, including two biggest chips. You can easily found guys with hot air at laptop/consoles service point, maybe at phone service point too.

Alternative way - try freezing spray (or compressed air can applied upside down) and hair drier. Maybe hot or cold temperatures temporary fix problem so You can narrow area then use hand solder.

If both methods fail, repair may required multichannel oscilloscope to locate broken component or track.


Title: Re: Guess who :)
Post by: Drewid on August 18, 2017, 07:57:06 AM
Thanks for the reply.

It's reasonably guess-able I think, the board layout is pretty logical so I know roughly where the problem is and could narrow it down further with just a tape measure.   I think I could get a hot air station fairly cheaply and I'm in no rush so can wait a few weeks for it to arrive from China if necessary.   It'd be a useful thing to have anyhow, it's a good excuse.   :)

I can be keeping an eye out for possible donor boards in the meantime.


Title: Re: Guess who :)
Post by: Ertew on August 25, 2017, 03:40:09 PM
One more thing. This digitizer contains two boards and flat flex to connect them.
You show active board (lot of chips) but not passive board (antennas). Flat cables shouldn't cause problems, but connectors at both ends may.


Title: Re: Guess who :)
Post by: Drewid on August 31, 2017, 09:28:41 PM
Well there you go. Good call. :)
Lower ribbon cable reseated.

[attachment=1]

Super happy bunny :)