Phone backlight puzzle - Page 1
Forum section: electronics / repair

author: PlainName
author_rank: Super Contributor
timestamp: December 11, 2024, 08:28:45 am
content: Got a nice phone (Xiaomi Mi A1 aka Tissot) which suffered from the touch screen not recognizing touch in a band across the screen. So I purchased a replacement screen (with frame) from Aliexpress and... didn't get around to fixing it - didn't want to end up with a part-dismantled phone, and the touch thing was mostly able to be worked around. But eventually I did replace the screen and it all worked great! Except GSM. Seems that I didn't connect the tiny coax connector properly, so took it apart again to fix that and managed to crack the screen.Got another screen off Aliexpress and this one shows how cheap they are being. The ally frame fixing tabs needed work with a needle file for the PCBs to fit, but otherwise it went OK and it works. Kind of. The display is washed out and needs brightness turned up high, and it is not as sharp as the original (or replacement, or a second one of these I have). So... yep, you guessed, ordered another screen from a more reputable, but still Aliexpress, store. This one looks good - the packaging is much more professional, the battery sticky tabs are in place, etc. And that's how we get to my question (sorry, thought the history might help fend off some questions):On power up the boot logo shows as normal, and the screen is lit up (albeit not at full brightness, but that's normal). Then that screen goes and the Android animated logo should show, but the screen is blank. If I get a torch and shine it on the screen I can see the LCD is indeed working, it's just that there is no backlight. Obviously, the backlight is bust in some way. But... it works for the initial power up so it can't be broken.Anyone got a clue as to how this could occur? I switched back to the previous frame and screen and that doesn't exhibit the issue, so it is something to do with this particular screen, but it works to start up...

author: amyk
author_rank: Super Contributor
timestamp: December 12, 2024, 03:23:03 am
content: If the backlight driver IC is on the panel itself, it could be incompatible with the original one. Hence why the default brightness works but when the OS loads the driver it commands it to the wrong state and it turns off.

author: u666sa
author_rank: Frequent Contributor
timestamp: December 12, 2024, 05:56:14 am
content: We don't take these kinds of phones into repair, because parts are trash and because customers are cheap. No money to be made here.Yes, your display assembly has to be replaced with the original xiaomi part.__ORIGINAL__Which you are not going to do, becuase at this point you might as well purchase a brand new phone.

author: PlainName
author_rank: Super Contributor
timestamp: December 12, 2024, 11:02:33 am
content: QuoteOh, there's a thought. But I would assume it would be OK even if not original else they wouldn't be able to sell these things. Well, they could sell them but they'd have an awful lot of returns!

author: PlainName
author_rank: Super Contributor
timestamp: December 12, 2024, 11:08:25 am
content: QuoteIf a new phone was available at a sensible price I would be tempted! But they don't make them any more and this particular model was perfect for my purposes. I have a replacement which is OK (better in some respects, worse in others) but I would like to have my old one working again as a standby.

author: amyk
author_rank: Super Contributor
timestamp: December 13, 2024, 03:38:51 am
content: Quote from: PlainName on December 12, 2024, 11:02:33 amPerhaps there's a difference that earlier (or later) versions of the software were sensitive to.The FTDI fiasco should've taught everyone that compatible, doesn't always mean 100% compatible.I haven't researched the details but it might be possible to get the replacement to work with a software change.

author: PlainName
author_rank: Super Contributor
timestamp: December 13, 2024, 11:07:10 am
content: I think a software change is probably beyond me, if for no other reason than I want to keep this particular version. I have another one of these (white gold case, yuk) but that runs LineageOS and suffers for it (although LOS itself is great and in other circumstances would be fine). This particular phone is still running the latest official release, which I rather like.Yeah, I know this sounds a bit picky but that's the nature of this project - it is mostly an emotional thing. Looked at dispassionately it makes no sense since the phone is crap for nowadays. For instance, WiFi runs down the battery super quickly now all the access points are WiFi6 (no idea what that's about, but worked around with a util to disable WiFi when the phone isn't being used). But there are good things too, like Google Messages actually being usable, not having RCS crap and allowing more than 5 characters on input before a line feed. So, unfortunately, even if it did turn out that a software change would fix it I'm not sure it would be worth doing

author: PlainName
author_rank: Super Contributor
timestamp: December 20, 2024, 11:16:08 am
content: To round this off...Went to the Aliexpress supplier, who have a shop and do their own customer service, and explained the issue. They said they can either give a partial refund or have it returned, and although I tried to explain I wasn't after either and just wanted to understand how it couldn't work but still power on OK, we resolved it by doing a free return and re-ordering. However, I ordered from a different supplier who was shipping what looked like the same thing (same product photos and packaging).That arrived yesterday and isn't the same: no cardboard box or battery sticky pads, for instance. But otherwise looked fine so I gave it a go and it works perfectly.Wish I'd done a partial refund instead of free return now, then I could've tried to figure out the problem with the other screen. But knowing my luck I'd break something else when trying stuff so it's probably for the best

author: u666sa
author_rank: Frequent Contributor
timestamp: December 20, 2024, 01:40:59 pm
content: Bingo! It's a hit or miss with these things. We don't get our stuff from ali, we get it from local suppliers, parts shipped by couriers same or next day. We can return stuff for credit in the store. However, it's the time wasted. Plus you get angry customer, where is my phone it should have been done yesterday, give it back to me. So often you end up with time spend, no money, and time lost to credit in the store.In other words, these phones are time wasters.We just don't do them.

author: PlainName
author_rank: Super Contributor
timestamp: December 20, 2024, 02:25:34 pm
content: Yes, I appreciate that for a professional repairer, and I accept that my time on this is worth less than the £10 the replacement cost. What was bugging me was not understanding how the fault could occur: the backlight worked, the LCD worked, the PCBs were OK and when powered on it was good. But moving past the boot code the backlight was dead.