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7.0 TFT 800x480 w/touchscreen- No picture
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7.0 TFT 800x480 w/touchscreen- No picture

by brollings on Tue Nov 21, 2017 2:57 pm

I purchased the 7"TFT 800x480w/touchscreen (http://adafru.it/2354), and the TFP401 HDMI/DVI decoder w/touch (http://adafru.it/2219) I plugged the proper wires into their proper locations into all components. power everything up, no image....plug the pi into a monitor that works and the device displays proper.
things I've tried: Dedicated 2.4amp 5v connection for both, raspberry pi 2 b, arduino mega 2560. plugging the hdmi input into hdmi out on computer. nothing boots an image or back light. applying 3.3-5v dc to the back light pins does nothing. plugging into a computer changes my image on computer to 800-480 senses a hdmi out put device, no image on TFT display .

My suspicion is the display is malfunctioning. I would like to exchange the part.
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Re: 7.0 TFT 800x480 w/touchscreen- No picture

by adafruit_support_carter on Sat Nov 25, 2017 2:11 pm

It looks like you're also using the extension ribbon cable. Have you tried testing without that and having the display directly connected to the TFP401 like this:
https://cdn-shop.adafruit.com/1200x900/2354-00.jpg

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Re: 7.0 TFT 800x480 w/touchscreen- No picture

by brollings on Sat Nov 25, 2017 3:32 pm

Yes, I just connected the 40 pin connector from the touchscreen into the hdmi decoder, no sign of life from the tft display.

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Re: 7.0 TFT 800x480 w/touchscreen- No picture

by adafruit_support_carter on Sat Nov 25, 2017 3:41 pm

OK. Let's continue trouble shooting with this more direct connection. Take a look at the info here:
https://learn.adafruit.com/adafruit-tfp ... -pi-config
and see if any of that helps.

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Re: 7.0 TFT 800x480 w/touchscreen- No picture

by brollings on Sat Nov 25, 2017 8:32 pm

Just got done turning on/off all the selections and testing the config.txt file. every selection has no effect. and it was considerably time consuming. Are there anymore tests to perform before I can get an exchange...

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Re: 7.0 TFT 800x480 w/touchscreen- No picture

by adafruit_support_carter on Sun Nov 26, 2017 2:24 pm

At this point it could be decoder breakout or the display. Not sure which. We know your Pi's HDMI works. And by connecting the display directly to the decoder we've removed the possibility of it being the extension cable. One detail is you haven't soldered any of the backlight jumpers:
https://learn.adafruit.com/adafruit-tfp ... /backlight
which, for the 7" display you are using shouldn't prevent it from working, it'll just make it dim.

I've tried: Dedicated 2.4amp 5v connection for both

"both" here means the Pi and the driver board? It could be a power issue, so this is a good check. Did you also try different USB cables?

plugging into a computer changes my image on computer to 800-480 senses a hdmi out put device, no image on TFT display .

This info comes from the EDID EEPROM on the decoder, so we know that at least works. But the display driver itself is a separate chip. So unfortunately, sensing the EDID info doesn't rule out the decoder board.

applying 3.3-5v dc to the back light pins does nothing.

Exactly which pin was this? The one on the decoder breakout?

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Re: 7.0 TFT 800x480 w/touchscreen- No picture

by brollings on Sun Nov 26, 2017 4:03 pm

applying 3.3-5v dc to the back light pins does nothing.

Exactly which pin was this? The one on the decoder breakout?[/quote]

The two pins on the decoder labeled (backlight and gnd) . When a pwm signal is applied no response from tft display.

Upon study I noticed the back light jumpers. So I Soldered both them... to make it 125mA (as depicted in illustration). Then port output a pwm pin to control back light. no response...

run test changing settings in config.txt
no response

"both" refers to both devices defined in initial statement. Both devices require a micro usb at 2.4 amp. The charging wires are new and designed for the application.

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Re: 7.0 TFT 800x480 w/touchscreen- No picture

by adafruit_support_carter on Sun Nov 26, 2017 11:47 pm

Do you have a multimeter? This would help determine if it's the display or the driver board. The backlight is very simple, so either it's bad on the display, or the driver board isn't supplying the voltage for some reason.

Not trying to drag this out, just trying to find the smoking gun.

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Re: 7.0 TFT 800x480 w/touchscreen- No picture

by brollings on Mon Nov 27, 2017 1:57 am

yes, where do I begin my probe-in...

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Re: 7.0 TFT 800x480 w/touchscreen- No picture

by adafruit_support_carter on Mon Nov 27, 2017 2:16 pm

Alright, see photo below. First, remove all the jumpers wires that are attached to the decoder breakout - the ones circled in yellow. You only need the EDID EEPROM attachments for programming a new EDID, the backlight will default to always on, and not sure what you have attached to the 3V3 pins. Once those wires are removed, hook up the decoder breakout to the Pi via USB and HDMI, like in your original photo. Power up the Pi. Then, measure the voltage at the 3 points indicated. You can reference to any of the available GND pins.
  • A - This is hidden in the photo, but there's a 5V pad between the USB and HDMI connecter. It is labeled 5V.
  • B - The 3V3 pin (this is the output of the LT1117 voltage regulator)
  • C - The solder point shown (this is the output of the FAN5333BSX LED driver)
test_points.png
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Re: 7.0 TFT 800x480 w/touchscreen- No picture

by brollings on Sun Dec 03, 2017 3:24 pm

(5v pin) A to ground = 5vdc
(3v pin) B to ground= 3vdc
(solder joint illustration)C to ground = 0vdc

( pins on eprom side)
5v=5vdc
gnd=ground continuity check positive
scl=5vdc
sda=5vdc

Now this diagnostic method indicates the decoder board may be faulty.

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Re: 7.0 TFT 800x480 w/touchscreen- No picture

by adafruit_support_carter on Mon Dec 04, 2017 1:17 pm

Now this diagnostic method indicates the decoder board may be faulty.

Seems possible. Thanks for making these measurements. The input voltages all look good, but seems like maybe the backlight voltage isn't there. Let's check that further. What reading do you get at the solder point on the opposite side of the part from point C? Point D in image below.

[EDIT] Also - are you making these measurements with the display attached?
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Re: 7.0 TFT 800x480 w/touchscreen- No picture

by brollings on Tue Dec 05, 2017 1:48 pm

voltage across (C and D) = 5vdc

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Re: 7.0 TFT 800x480 w/touchscreen- No picture

by adafruit_support_carter on Tue Dec 05, 2017 1:56 pm

Sorry, I meant between D and GND. And is the display attached?

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Re: 7.0 TFT 800x480 w/touchscreen- No picture

by brollings on Tue Dec 05, 2017 2:15 pm

still 5vdc. and yes the screen is still hooked up.

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