[GUIDE] 3.5 inch HDMI Display - high energy usage

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Vineheart01
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Re: 3.5 inch HDMI Display - high energy usage - WITH Fix

Post by Vineheart01 » Wed Dec 13, 2017 3:13 pm

Yeah i'll do that when i get home tonight, assuming i remember since i wont be getting home till late today lol.
None of my stuff is assembled yet so it'll be easy to read it all still. Literally all ive done with this hdmi build so far is mod the case, flash the SD card, and verify the screen works lol

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Re: 3.5 inch HDMI Display - high energy usage - WITH Fix

Post by Vineheart01 » Wed Dec 13, 2017 10:36 pm

Image

The bottom right one appears to be rubbed off or not even marked. I dont see anything whatsoever on it
The topright one is barely legible. That one took me about 5mins to even make out a single digit lol, not even sure if i read it right.

Knowing our luck, that bottom right one is the backlight controller and we have no idea what its called lol. Like i said, its not marked in the slightest, i dont even see the remnant of a letter/digit somewhere.

edit: Poked at it with an ohmmeter: sure enough, the (looking at the image) left pin of the backlight switch is connected to the topright pin of that mystery chip. Awesome....

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Re: 3.5 inch HDMI Display - high energy usage - WITH Fix

Post by salami738 » Fri Dec 15, 2017 2:01 pm

Vineheart01 wrote:
Wed Dec 13, 2017 10:36 pm
The bottom right one appears to be rubbed off or not even marked. I dont see anything whatsoever on it
The topright one is barely legible. That one took me about 5mins to even make out a single digit lol, not even sure if i read it right.

Knowing our luck, that bottom right one is the backlight controller and we have no idea what its called lol. Like i said, its not marked in the slightest, i dont even see the remnant of a letter/digit somewhere.

edit: Poked at it with an ohmmeter: sure enough, the (looking at the image) left pin of the backlight switch is connected to the topright pin of that mystery chip. Awesome....
Thanks a lot for the picture of your board and the infos. Our current findings are:
Image

Why is the mystery chip connected to the touch controller? :?

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Re: 3.5 inch HDMI Display - high energy usage - WITH Fix

Post by salami738 » Sat Dec 16, 2017 1:00 am

Made some progress last night:
Image

Atm I think the mysterious chip has to be a companion of the touch controller and is useless for us.
But the upper left corner looks suspiciuos. I think these are MOSFET's driven by the Main chip (PWM?), supplied by 5V0.

And I noticed, that I can hear the backlight in the audio signal on my loudspeaker. I think the manufacturer hasn't applied proper filtering between the backlight driver and the 5V0 rail.

My first reverse engineering project and I like it! :D

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Re: [SOLVED] 3.5 inch HDMI Display - high energy usage

Post by salami738 » Sat Dec 23, 2017 11:48 am

The main problem is solved. Maybe some mod wants to move this to the GUIDEs section of the forum?

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Re: [SOLVED] 3.5 inch HDMI Display - high energy usage

Post by YaYa » Sat Dec 23, 2017 12:12 pm

Moved this to the resolved section.
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Re: [GUIDE] 3.5 inch HDMI Display - high energy usage

Post by moosethemucha » Sun Jan 14, 2018 7:46 pm

Great guide - Currently in process of modding the screen to use less power - Thank you for everyones work.

I had a question about the screen - Has anyone gotten HDMI audio working ?

I cant seem to get it to work - does it require the GPIO header to be plugged in ? From what i could tell thats only needed for touch screen options.

I was also unable to get anything from audio on both Ubuntu 16.04 and Mac osx Seirra - both detected (including the pi) that HDMI audio was there but I couldn't hear anything ?

Does it require a special driver or something - I didn't install the 99-fbturbo.conf-HDMI as it fails during the driver install. But isn't this just for touch screen stuff ? https://github.com/goodtft/LCD-show

I would prefer to use the HDMI audio that way I could get rid of the USB DAC I'm using - meaning no usb stuff for my build which would be a great power save.

I'm going to have a look at the HDMI DAC to Headphone IC skematics and see how that works.

Do you need to amplify the signal before hand ?

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Re: [GUIDE] 3.5 inch HDMI Display - high energy usage

Post by moosethemucha » Mon Jan 15, 2018 9:41 pm

I've now removed the usb port and backlight control switch and it seems that the 5v0 rail is being sent to ground. The butchering that I've done - I tried to scrape away some stuff around the port to see if that would fix it - it didn't. When working on the board are people removing the screen from the main board or just leaving it in place - im not a massive fan of these soldered on ribion cables but I think on the next one I'll give that a go. Also the butchering was mainly due to me not having a decent chisel tip soldering iron - I had to use a small tip which makes desoldering hard - in the end I got inpatient and cut away the header - after this the board and screen did work - then when I attempted to desolder the usb port and switch shit got a bit fucked - hence the butchering.

Im hoping maybe someone has found another spot to provide 5v to the screen - I've already ordered an new screen but it would be nice if I could get this one working. What Im thinking is to remove the screen from the board (I've done something like this with a composite screen build i did) - I've now got a nice large chisel bit which should make things easier. Then cut away that corner and see if i can reconstruct the 5v coming in from the usb port.

Could someone please take a super hi res photo of that section (I know this is asking alot) but it would make things a little easier - I'm hoping that this may also lead to figuring out if we can bypass all 5v all together.

Attached are the pictures
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Re: [GUIDE] 3.5 inch HDMI Display - high energy usage

Post by moosethemucha » Tue Jan 23, 2018 10:17 pm

So I've been able to get the screen up and running - but during the last week I wasn't super careful with the screen and cracked it - at least I thought I had, and I did. I was able to solder off the screen which made desoldering the header alot easier. I've got another screen on order but I''d like to see if I can get a replacement screen minus the controller and solder it on - I would assume that they'd be fairly cheap. Would anyone know of a replacement, and where to buy it ?

I've found this one but Im not 100% sure if its suitable - will need to investigate more - but $10 is better than $30.
https://www.aliexpress.com/item/3-5-inc ... utifyAB=5
I'll upload some pics later with some board alterations.

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Re: [GUIDE] 3.5 inch HDMI Display - high energy usage

Post by salami738 » Thu Feb 08, 2018 12:45 am

moosethemucha wrote:
Mon Jan 15, 2018 9:41 pm
...
Im hoping maybe someone has found another spot to provide 5v to the screen - I've already ordered an new screen but it would be nice if I could get this one working. What Im thinking is to remove the screen from the board (I've done something like this with a composite screen build i did) - I've now got a nice large chisel bit which should make things easier. Then cut away that corner and see if i can reconstruct the 5v coming in from the usb port.
...
Hi,
just saw your post, I got no email about answers, so I was late.
I will check if there is a alternate connection to the 5V rail, if the header and micro USB port is desoldered.
But you have to make sure you don't have any shorts between 5V and GND or you will burn the traces on the board.

greetings from germany!
Last edited by salami738 on Thu Feb 08, 2018 1:21 am, edited 1 time in total.

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