TFP401 Backlight Driver not working?

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rmeuth
 
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TFP401 Backlight Driver not working?

Post by rmeuth »

I have the Adafruit 5" 800x480 display hooked up to the TFP401 board, and it looks like the backlight driver is not working. In bright light, I can see that the display is showing what is provided over HDMI (connected to my laptop), and I've hooked the display up to an RA8875 board to make sure it works as well. The HDMI light turns on, and the power light is on as well, but a little dim, which seems weird. Windows makes the new device sound and detects the display when I plug it into my computer, and I can choose it from display settings, with the right characteristics.

I poked around on the board with a multimeter, and verified that it's getting 5V on VIN, from both USB or the input wires I soldered and the on-board 3.3V regulator is generating the right voltage. I *think* I was checking the 24V signal for the backlight (the output of the smaller diode near the corner of the board, but saw only around 5.14V.

Pictures attached, is there anything else I can check or do to make this work?
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mikeysklar
 
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Re: TFP401 Backlight Driver not working?

Post by mikeysklar »

Thank you for providing the photos. That helps us understand your setup quickly.

What size power supply are you using for the TFP401 / display? The current draw should be able 500mA for the display on full power.

Did you attempt to use the PWM backlight control?
You can even power the display and decoder from a USB port. For example, with a 5" 800x480 display and 50mA backlight current, the current draw is 500mA total. You can reduce that down 370mA by running the backlight at half-brightness (25mA). With the backlight off, the decoder and display itself draws 250mA. If you want more backlight control, there's a PWM input, connect that to your microcontroller or other PWM output and you can continuously dim the backlight as desired

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rmeuth
 
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Re: TFP401 Backlight Driver not working?

Post by rmeuth »

Thanks for the suggestions! I've tried powering using the USB port on my laptop, and a wall USB charger that can provide 2A, and a breadboard power supply that is rated for 500mA. None of these work.

I hadn't used the PWM backlight line. Using my highest current source and connecting the backlight signal to GND, 5V, and 3.3V gives no change. I tried driving it using PWM from an Arduino at various duty cycles, no difference also.

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mikeysklar
 
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Re: TFP401 Backlight Driver not working?

Post by mikeysklar »

I'm up for recommending display replacement, but just need to understand the original photos better.

Thank you for clarifying the power supplies you have tried. We can eliminate those as culprits.

When you switched to the RA8875 and ran a test program that looks as though the backlight is working correctly.

The photos with HDMI connected to the TFP401 look like an unusual ribbon cable. Do you have another HDMI cable you can use? Is the resolution set to 800x480? Depending on what your laptop is running for an OS that can be a difficult setting.

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rmeuth
 
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Re: TFP401 Backlight Driver not working?

Post by rmeuth »

Yeah, the display works correctly connected to the RA8875, it looks great. This means to me that the display itself is fine.

I was using one of the Adafruit DIY HDMI cable setup, but I swapped it out for a regular HDMI cable. With either it is correctly detected by windows as an 800x480 display, and I can enable it. Additionally, with either the regular or DIY HDMI cable, if I take the display into bright light, I can see that it is showing my laptop screen - I can very dimly see when I move windows around - it is super hard to capture this in a picture, but you can see a little bit of a white window on the original picture. I think it is just not backlit using this TFP401 board.

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mikeysklar
 
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Re: TFP401 Backlight Driver not working?

Post by mikeysklar »

Since you are using the 5" screen you will want to modify the TFP401 jumper (solder it closed) get you another 25mA. It is supposed to be outputting 25mA by default and 50mA is typically needed for the 5" to look good.
adafruit_products_25ma.jpg
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rmeuth
 
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Re: TFP401 Backlight Driver not working?

Post by rmeuth »

I did do that already, you can see that I've soldered the +25mA jumper in the picture I posted.

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mikeysklar
 
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Re: TFP401 Backlight Driver not working?

Post by mikeysklar »

I see you have.

Well we can replace the TFP401 driver for another.

I'm tempted to say try the 100mA jumper, but the instructions don't advise that so probably best to swap it.

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rmeuth
 
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Re: TFP401 Backlight Driver not working?

Post by rmeuth »

Ok, thank you so much for your help. What is my next step to get a replacement?

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mikeysklar
 
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Re: TFP401 Backlight Driver not working?

Post by mikeysklar »

Please email [email protected] for replacement assistance. They will need your order# for the TFP401 and this forum link a authorization.

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rmeuth
 
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Re: TFP401 Backlight Driver not working?

Post by rmeuth »

Wonderful, thank you so much!

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