I have a spare Taranis that developed a LCD with no or very low contrast, the back LED lights are fine. The rest of the Tx works perfectly. By lowering the brightness and increasing contrast to max, I can just read the lcd at the right angle. I bought a replacement LCD from Aloft and same. Not knowing, I should of bought the main board.
I also tried reseating the LCD ribbon cable, no love. It must be something on the main board. I am pretty good with electronics and excellent soldering, I just don't have the schematic to start troubleshooting. Any suggestions where to start looking on the main pcb? Even a p/n to the LCD would help with the LCD pinout or pin numbers driving the LCD. Another thread to ask in? TIA!!!
Taranis LCD, no or very low contrast
Re: Taranis LCD, no or very low contrast
Taranis or Taranis Plus? They use different (and incompatible) LCDs. Make sure you ordered the right one.
Re: Taranis LCD, no or very low contrast
Regular Taranis, I already swapped it, and it works the same, barely readable.
Re: Taranis LCD, no or very low contrast
More info, not solved yet. I scoped and pinned out the LCD connector. I was hoping to find an analog signal to adjust the LCD contrast (I have seen this before on a digital goto telescope (LX200GPS-14"). The LCD pin number #3 is a strange voltage, I adjusted the contrast while watching this pin, and it does not change voltage levels, even on a good Taranis. Four other pins are switching 0-3v. Any ideas or suggestions welcome.
LCD Pin#
1 3v
2 0v
3 Switching 1.4v to 1.6v ??? Unknown where this connects.
4 0v
5 Switching 0-3v Connects to STM32 pin#5
6 Switching 0-3v Connects to STM32 pin#6
7 0v
8 0v
9 3v
10 Switching 0-3v Connects to STM32 pin#58
11 3v
12 3v
13 3v
14 3v
15 3v
16 3v
17 3v
18 Switching 0-3v Connects to STM32 pin#57
19 0v
20 3v
LCD Pin#
1 3v
2 0v
3 Switching 1.4v to 1.6v ??? Unknown where this connects.
4 0v
5 Switching 0-3v Connects to STM32 pin#5
6 Switching 0-3v Connects to STM32 pin#6
7 0v
8 0v
9 3v
10 Switching 0-3v Connects to STM32 pin#58
11 3v
12 3v
13 3v
14 3v
15 3v
16 3v
17 3v
18 Switching 0-3v Connects to STM32 pin#57
19 0v
20 3v
Re: Taranis LCD, no or very low contrast
All your measurements match what I can see. Pin 3 is unconnected.
The only thing that looks strange is your supply voltage, should be 3.3V, not 3V, would be looking at that first.
The only thing that looks strange is your supply voltage, should be 3.3V, not 3V, would be looking at that first.
Re: Taranis LCD, no or very low contrast
Good point, I looked closer at the voltage levels.
Looking at the Ti TPS5401 (U3) buck regulator,
R76=29.4K
R77=10.0K
Vfb=0.8V
Vout calc = 3.152V
I measured on my good Taranis:
R76=29.33K
R77=9.97K
Vfb=0.8
Vout calc = 3.146V.
I measured my good and bad Taranis LCD voltage = 3.124V and 3.129V. ~23mV should not be out of spec.
Any other ideas to look at? Thanks.
Looking at the Ti TPS5401 (U3) buck regulator,
R76=29.4K
R77=10.0K
Vfb=0.8V
Vout calc = 3.152V
I measured on my good Taranis:
R76=29.33K
R77=9.97K
Vfb=0.8
Vout calc = 3.146V.
I measured my good and bad Taranis LCD voltage = 3.124V and 3.129V. ~23mV should not be out of spec.
Any other ideas to look at? Thanks.