thayerhughes
Posts: 1
Joined: Mon May 08, 2017 11:38 pm

Re: Waveshare 7" touch screen not working

Tue May 09, 2017 12:27 am

-- FLASHING SCREEN SOLVED --
For what it's worth to anyone with a problematic Waveshare 7"-C HDMI 1024x600 LCD Rev 2.1, mine came in late last night and so, of course, I stayed up to configure and test it out. Life is never so simple. The editing of /boot/config went without a hitch and mine is set (having commented out any overscan and framebuffer entries that I use for other LCDs) with:

hdmi_group=2
hdmi_drive=1
hdmi_ignore_edid=0xa5000080
hdmi_mode=87
hdmi_cvt=1024 600 60 6 0 0 0

The screen booted up fine and displayed correctly, but the backlight kept cycling on and off. The cycles might change in duration and spacing depending on how I was fiddling with it and I soon discovered that if I held it with my finger in a certain place on the back that the screen would stay on indefinitely. Upon VERY close inspection with a loupe and strong light I realized that the 103 resister nearest the upper-right corner (when looking at the back of the LCD board) had a micro fracture in it. To be more clear, the resister that's at the far edge from the HDMI and USB connectors and at about the same level. It looks like a pull-down connected to the ground plane and was probably cracked when it was placed and soldered.

I couldn't quickly dredge up a 103 but I did find some 104's on a defunct CO2 detector/alarm, so I parallel soldered one of those to the 103. (If you can't solder micro parts then get some help.) After a day now the screen has been working beautifully and consistently, and hopefully we will all live happily ever after.

The end


PS. I initially skyped Waveshare but they're on China time and I'm impatient and don't speak the lingo. I'll probably leave a critical review on Amazon (where I purchased it) as the display was obviously not QA'd before shipping, but I DO like the display now that it's working. Here's contact info if you need it:
(sales) sales@waveshare.com
(after-sales) service@waveshare.com
(complaint) complaint@waveshare.com
(apply for distributor) distributor@waveshare.com

Skype: wvshare
Whatsapp: 86-18923750395
Tel: 86-755-82807524
Fax: 86-755-83042572

Address: Waveshare Electronics
Rm 813, Dynamic World Building, Zhenhua Rd, Futian District, Shenzhen, China

infrared
Posts: 2
Joined: Tue Jan 10, 2017 6:26 pm

Re: Waveshare 7" touch screen not working

Sat Jul 22, 2017 3:55 pm

Upon VERY close inspection with a loupe and strong light I realized that the 103 resister nearest the upper-right corner (when looking at the back of the LCD board) had a micro fracture in it. To be more clear, the resister that's at the far edge from the HDMI and USB connectors and at about the same level. It looks like a pull-down connected to the ground plane and was probably cracked when it was placed and soldered.
My eyes are obviously not what they once were. I must have missed that cracked resistor a dozen times. Nice job!

Unfortunately, in my case, the pick and place machine damaged the board at the same time it was cracking that resistor. The top of that resistor connects to a 5v signal coming from the backlight's on/off switch. As far as I could determine, the bottom of that resistor is intended to be soldered to a "via hole" in the board, which leads to a different layer and routes to the enable pin (EN, pin #4) of the PT4103 chip. In my case, the board's via which sits under the bottom of the resistor had torn away from the board, leaving no pad for soldering the new resistor.

I made several unsuccessful attempts to get a new resistor installed, then started reading the PT4103 datasheet a bit more carefully. It says, "A high input at EN enables the device and a low input disables the devices. When not used, connect EN to the input source for automatic startup." Well, the "input source" pin on the chip is simply the positive rail of the power supply, so that told me I could eliminate that resistor entirely, and use a jumper wire to tie the EN pin directly to the switched 5v from the on/off switch -- which is exactly what I did.

The switch still works, and my backlight is no longer going dark unless I turn it off with the switch.

I'm not sure why that pull-up resistor was installed between the switch and the EN pin. I assume it was there to enable something else to pull the EN pin down even if the switch was in the ON position.

After running the backlight for a couple of weeks to confirm that my intermittent problem is gone, I may replace the jumper wire with another resistor. With a resistor in place, one of the Pi's GPIO pins should be able to safely pull the EN pin of the PT4103 low via software.
Attachments
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redgod
Posts: 5
Joined: Thu Sep 10, 2015 1:14 pm

Re: Waveshare 7" touch screen not working

Fri Jul 28, 2017 1:06 pm

infrared wrote:
Sat Jul 22, 2017 3:55 pm
Upon VERY close inspection with a loupe and strong light I realized that the 103 resister nearest the upper-right corner (when looking at the back of the LCD board) had a micro fracture in it. To be more clear, the resister that's at the far edge from the HDMI and USB connectors and at about the same level. It looks like a pull-down connected to the ground plane and was probably cracked when it was placed and soldered.
My eyes are obviously not what they once were. I must have missed that cracked resistor a dozen times. Nice job!

Unfortunately, in my case, the pick and place machine damaged the board at the same time it was cracking that resistor. The top of that resistor connects to a 5v signal coming from the backlight's on/off switch. As far as I could determine, the bottom of that resistor is intended to be soldered to a "via hole" in the board, which leads to a different layer and routes to the enable pin (EN, pin #4) of the PT4103 chip. In my case, the board's via which sits under the bottom of the resistor had torn away from the board, leaving no pad for soldering the new resistor.

I made several unsuccessful attempts to get a new resistor installed, then started reading the PT4103 datasheet a bit more carefully. It says, "A high input at EN enables the device and a low input disables the devices. When not used, connect EN to the input source for automatic startup." Well, the "input source" pin on the chip is simply the positive rail of the power supply, so that told me I could eliminate that resistor entirely, and use a jumper wire to tie the EN pin directly to the switched 5v from the on/off switch -- which is exactly what I did.

The switch still works, and my backlight is no longer going dark unless I turn it off with the switch.

I'm not sure why that pull-up resistor was installed between the switch and the EN pin. I assume it was there to enable something else to pull the EN pin down even if the switch was in the ON position.

After running the backlight for a couple of weeks to confirm that my intermittent problem is gone, I may replace the jumper wire with another resistor. With a resistor in place, one of the Pi's GPIO pins should be able to safely pull the EN pin of the PT4103 low via software.


Hi you could upload a picture with higher quality, I have the same problem that goes off and I want to test your hack, I do not understand much of electronica but if I have an image of better quality and see where soldaste help me a lot thanks and forgive my English

User avatar
entozoon
Posts: 25
Joined: Sun Feb 12, 2012 7:27 pm
Location: Sheffield, UK
Contact: Website

Re: Waveshare 7" touch screen not working

Mon Sep 04, 2017 4:14 pm

For anyone having trouble with this screen and a Raspberry Pi Zero W as I was, where the screen worked but no touch screen at all:
The solution was simply that it didn't have enough power - specifically that the Pi couldn't provide enough power from the USB for both the backlight and the touch support.

a.k.a. tl;dr, iirc, ngl, smh.. Use a powered USB hub.

(Or power it externally yourself, it's dead easy - cut the positive connection, bosh in your external power supply (more than 0.5A) and connect up the negatives)

chewiiie
Posts: 1
Joined: Thu Nov 15, 2018 8:52 am

Re: Waveshare 7" touch screen not working

Thu Nov 15, 2018 8:54 am

blackzoro wrote:
Mon Dec 05, 2016 1:29 am
I just use the 7 inch HDMI Waveshare display to connect to a rapsberry Pi 3.The wavesahre screen is not have any problem, but touch control is not possible normally.
movie
https://youtu.be/K2NBaOFcqeg
Hello,

Did you find a solution for that touch issue ? I have the same problem on my Waveshare 7inch HDMI C display / Pi2B.

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