Display 1: I followed the tutorial https://docs.arduino.cc/learn/electronics/lcd-displays/ . The display turned on, but nothing was shown on it. Some seconds (or a minute) later I smelled something was burning. I could see some smoke coming from the Vdd pin, or somewhere between the vdd and vss pins, which are connected to 5v (arduino) and GND (arduino), respectively. I disconnected everything and checked the display. I detected with the multimeter that vdd and vss were shorted. Wether this is the cause of the display's failiure or a consequence, I dont know.
I decided to try another display.
Display 2: this time I used the same type of display, but attached an I2C module, so I only had to connect Vcc, gnd, sda and scl. I checked there where no shorts between pins both on the display and on the module. This time I only connected vcc and gnd to arduino's 5v and gnd. I just wanted to check if it turned on. It did. But some seconds later the display turned off (fried, actually), and I saw smoke coming from the same spot. Then I disconnected everything, and checked for shorts, and again, vss and vdd were shorted!
Now I'm thinking that maybe this vss-vdd short is a consequence and something else is causing the failure, but what? Could my Arduino Uno be the problem?
Next, I'm thinking of trying a different Uno, but I dont want to burn another display.
The arduino was powered using the USB.
I have no picture of the the first case, since I just disconnected it without thinking much. The second time I just connected vcc and gnd so, nothing much to show.
If you have a voltmeter, I'd be measuring what the actual voltage is at the device, both AC and DC. Something's terribly wrong, if you're sure you didn't reverse the power connections.
Thanks for your reply. I am sure I didnt mix them up. My voltmeter switches to DC or AC automatically. It shows 5.16 V DC at the 5V pin from Arduino when the display and IC2 module are not connected.
When they are connected, 4.7 V DC (but there is variation of around +- 0.05 V) at the Arduino 5V source, I2C's vcc and display's Vdd.
Never happened to me something like that, and I used a dozen of 1602 LCDs, most of them I2C, but also directly connected to Arduino (but I2C is the best and current solution for me), and even as shields.
So as you don't seem to have power issues from your Arduino, it sounds like a batch of defective displays to me, especially if you got both from the same reseller (can you tell us which one?).
I'd ask for a refund or at least a replacement, but in any case in the meantime I'd buy another one from a different shop/reseller.
