Fake 4n33?

My 100 4n33 optocouplers from AliExpress seem to be defective or fake. First, no good pin 1 markings, so I assumed bottom left when the label is upright but they never let the Arduino pin go higher then 0.7 volts. Take it out and the Arduino pin goes HIGH. I double checked my resistors and they seem correct.

Grind or crack one open to see if there is anything inside.

Did you try them, turned 180 degrees?

Yes, 180 deg made no difference. With a multimeter in diode check mode, there seems to be a LED from pin 1 to 2, and two diode drops from pin 6 to 4 as expected according to the datasheet.

I setup a breadboard to test my 4N33 chips. They work fine on the breadboard but in the pcb the unconnected pin 6 (output transistor base) is left floating and somehow picks up stray voltage which partially turns on the 4N33’s output transistor(s). The only source for this stray voltage I can think of is the left behind solder resin. Adding a 5K pullup on the Arduino’s input helps (10K didn’t work yet) but better yet is to add a large (>100K) pull down resistor on the 4N33’s pin 6. Am I the only one with this issue? Wondering if the PCB designers want/should add this pull down R.

1 Like

Hi, 4n33 didn’t work no matter what I did. I set up the 4n33 test circuit and it was solid in the test. All pcb is perfect. The pcb I used in the test is working normally. I’m changing arduno, it doesn’t work. Arduino nano v3 picks 4n33?

Did you read the solution for my china 4n33 optos?

To Arduino nano input (5v pin). I had to install a 5k resistor. Did I get right.

I need to connect 6 Pin 5k resistor to 4n33. It’s not an Arduino.

this way?


1 Like

Brother, you are great, the picture was very explanatory. I guess the leakage voltage connected to the diode on the 6 pin pcb. I noticed but it’s a little late

I connected a 100k resistor to 6 pins. there is no solution. where could i be doing wrong. I also tried different circuits.

These same optos work in a test breadboard?

I collect new PCB does not work well. I had previously happened to me, I changed the Arduino and I found the solution. There are 3 different Arduino, none of them solutions. I’ve added a 100k resistor 6-pin and still did not work.