Fake 4n33?

20200728_164602
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.
20200728_165527

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?

@Bestgart
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?

image

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.