A simple way to test optocouplers was needed. I don’t often “communicate” with them, but there are times when I need to determine whether the optocoupler is to blame?.. For these purposes I made a very simple probe. "Construction of the Weekend Hour."
Probe appearance: 
The circuit diagram of this probe is very simple: 
Theory:
Optocouplers (optocouplers) are installed in almost every switching power supply for galvanic isolation of the feedback circuit. The optocoupler contains a conventional LED and a phototransistor. To put it simply, this is a kind of low-power electronic relay with short-circuit contacts.
The principle of operation of the optocoupler: When an electric current passes through the built-in LED, the LED (in the optocoupler) begins to glow, the light hits the built-in phototransistor and opens it.
Optocouplers are often available in Dip package
The first leg of the microcircuit, according to the standard, is designated by a key, a dot on the body of the microcircuit, which is also the anode of the LED, then the numbers of the legs go along the circumference, counterclockwise.
The essence of the test: Phototransistor, when light from the internal LED hits it,
goes into an open state, and its resistance will decrease sharply (from a very high resistance, to about 30-50 Ohms).
Practice:
The only disadvantage of this probe is that to test it is necessary to unsolder the optocoupler and install it in the holder according to the key (my role as a reminder is the test button - it is shifted to the side, and the optocoupler key must face the button).
Next, when you press the button (if the optocoupler is intact), both LEDs will light up: The right one will signal that the optocoupler LED is working (the circuit is not broken), and the left one will signal that the phototransistor is working (the circuit is not broken). 
(I only had a DIP-6 holder and had to fill the unused contacts with hot glue.)
For final testing, it is necessary to turn the optocoupler “off key” and check it in this form - both LEDs should not light up. If both or one of them are on, then this tells us about a short circuit in the optocoupler.
I recommend this probe as a first one for beginning radio amateurs who need to check optocouplers every six months or a year)
There are also more modern circuits with logic and signaling of “out of parameters,” but these are needed for a very narrow circle of people.
I advise you to look in your “bins”, it will be cheaper, and you won’t waste time waiting for delivery. Can be removed from boards.
Add to favorites Liked +73 +105Description, characteristics, Datasheet and methods for testing optocouplers using the example of PC817.
Continuing the topic “Popular radio components for repairs of switching power supplies,” we will analyze one more part - optocoupler (optocoupler) PC817. It consists of an LED and a phototransistor. They are not electrically connected to each other, due to which, based on PC817 it is possible to implement galvanic isolation of two parts of the circuit - for example, with high voltage and with low voltage. The opening of the phototransistor depends on the illumination of the LED. I will discuss how this happens in more detail in the next article, where in experiments, by feeding signals from the generator and analyzing it with an oscilloscope, you can understand a more accurate picture of the operation of the optocoupler.
In other articles I will talk about the non-standard use of optocouplers, first in the role, and in the second. And using these circuit solutions I will build a very simple optocoupler tester. Which does not need any expensive or rare devices, but only a few cheap radio components.
The item is not rare and not expensive. But a lot depends on it. It is used in almost every popular (I don’t mean any exclusive) switching POWER SUPPLY and plays the role of feedback and most often in conjunction with the very popular radio component TL431
For those readers who find it easier to perceive information by ear, we recommend watching the video at the very bottom of the page.
Optocoupler (Optocoupler) PC817
Brief characteristics:
Compact body:
- pin pitch – 2.54 mm;
- between rows – 7.62 mm.
The PC817 is manufactured by Sharp; there are other manufacturers of electronic components that produce analogues, for example:
- Siemens – SFH618
- Toshiba – TLP521-1
- NEC-PC2501-1
- LITEON – LTV817
- Cosmo – KP1010
In addition to the single PC817 optocoupler, other options are available:
- PC827 - dual;
- PC837 – built;
- PC847 – quadruple.
Checking the optocoupler
To quickly test the optocoupler, I conducted several test experiments. First on the breadboard.
Option on breadboard
As a result, we were able to obtain a very simple circuit for testing the PC817 and other similar optocouplers.
First version of the scheme
I rejected the first option for the reason that it inverted the transistor markings from n-p-n to p-n-p
Therefore, to avoid confusion, I changed the diagram to the following;
Second version of the scheme
The second option worked correctly, but it was inconvenient to solder the standard socket
for a microcircuit
Panel SCS-8
Third version of the scheme
The most successful
Uf is the voltage on the LED at which the phototransistor begins to open.
in my version Uf = 1.12 Volts. 
The result is a very simple design.
Using the proposed probe, you can check NE555 (1006VI1) microcircuits and various optodevices: optotransistors, optothyristors, optosimistors, optoresistors. And it is with these radioelements that simple methods do not work, since simply ringing such a part will not work. But in the simplest case, you can test the optocoupler using the following technology:
Using a digital multimeter:
Here 570 is the millivolts that drop at the open junction of the optotransistor. In the diode continuity mode, the drop voltage is measured. In the “diode” mode, the multimeter outputs a pulse voltage of 2 volts, rectangular in shape, to the probes through an additional resistor, and when the P-N junction is connected, the ADC of the multimeter measures the voltage dropping across it.
Optocoupler and IC tester 555
We advise you to spend a little time and make this tester, since optocouplers are increasingly used in various amateur radio designs. And I’m generally silent about the famous KR1006VI1 - they install it almost everywhere. Actually, the 555 chip under test contains a pulse generator, the functionality of which is indicated by the blinking of LEDs HL1, HL2. Next comes the optocoupler probe.
It works like this. The signal from the 3rd leg 555 through resistor R9 reaches one input of the diode bridge VDS1, if a working emitting element of the optocoupler is connected to contacts A (anode) and K (cathode), then current will flow through the bridge, causing the HL3 LED to blink. If the receiving element of the optocoupler is also working, then it will conduct current to the base of VT1, opening it at the moment of ignition of HL3, which will conduct current and HL4 will also blink.
P.S. Some 555s do not start with a capacitor in the fifth leg, but this does not mean they are faulty, so if HL1, HL2 do not blink, short-circuit c2, but if even after that the indicated LEDs do not blink, then the NE555 chip is definitely faulty. Good luck. Sincerely, Andrey Zhdanov (Master665).
Instructions
If an optocoupler, the serviceability of which is specified under, is soldered into the board, it is necessary to disconnect it, discharge the electrolytic capacitors on it, and then unsolder the optocoupler, remembering how it was soldered.
Optocouplers have different emitters (incandescent lamps, neon lamps, LEDs, light-emitting capacitors) and different radiation receivers (photoresistors, photodiodes, phototransistors, photothyristors, phototriacs). They are also pinned. Therefore, it is necessary to find information about the type and pinout of the optocoupler either in a reference book or datasheet, or in the circuit diagram of the device where it was installed. Often, the pinout of the optocoupler is printed directly on the board of this device. If the device is modern, you can almost certainly be sure that the emitter in it is an LED.
If the radiation receiver is a photodiode, connect an optocoupler element to it and connect it, observing the polarity, in a chain consisting of a constant voltage source of several volts, a resistor designed so that the current through the radiation receiver does not exceed the permissible value, and a multimeter operating in measurement mode current at the appropriate limit.
Now put the optocoupler emitter into operating mode. To turn on the LED, pass through it in direct polarity a direct current equal to the rated one. Apply the rated voltage to the incandescent lamp. Using caution, connect the neon lamp or light-emitting capacitor to the network through a resistor with a resistance of 500 kOhm to 1 MOhm and a power of at least 0.5 W.
The photodetector must react to the inclusion of the emitter with a sharp change in mode. Now try turning the emitter off and on several times. The photothyristor and photoresistor will remain open even after the control action is removed until their power is turned off. Other types of photodetectors will react to every change in the control signal. If the optocoupler has an open optical channel, make sure that the reaction of the radiation receiver changes when this channel is blocked.
Having made a conclusion about the state of the optocoupler, de-energize the experimental setup and disassemble it. After this, solder the optocoupler back into the board or replace it with another one. Continue repairing the device that includes an optocoupler.
An optocoupler or optocoupler consists of an emitter and a photodetector separated from each other by a layer of air or a transparent insulating substance. They are not electrically connected to each other, which allows the device to be used for galvanic isolation of circuits.
Instructions
Connect the measuring circuit to the photodetector of the optocoupler in accordance with its type. If the receiver is a photoresistor, use a regular ohmmeter, and the polarity is not important. When using a photodiode as a receiver, connect the microammeter without a power source (positive to the anode). If the signal is received by a phototransistor of the n-p-n structure, connect a circuit of a 2 kilo-ohm resistor, a 3-volt battery and a milliammeter, and connect the battery with the positive side to the collector of the transistor. If the phototransistor has a p-n-p structure, reverse the polarity of the battery connection. To check the photodinistor, make a circuit of a 3 V battery and a 6 V, 20 mA light bulb, connecting it with the positive side to the anode of the dinistor.
In most optocouplers, the emitter is an LED or an incandescent light bulb. Apply the rated voltage to an incandescent light bulb in either polarity. You can also apply alternating voltage, the effective value of which is equal to the operating voltage of the lamp. If the emitter is an LED, apply a voltage of 3 V to it through a 1 kOhm resistor (positive to the anode).
Tester for checking optocouplers
Failure of an optocoupler is a rare situation, but it does happen. Therefore, when soldering a TV for parts, it would not be superfluous to check the PC817 for serviceability, so as not to later look for the reason why the freshly soldered power supply does not work. You can also check the optocouplers that came from Aliexpress, not only for defects, but also for compliance with the parameters. In addition to dummies, there may be specimens with inverted markings, and faster optocouplers may actually turn out to be slow.
The device described here will help determine both the serviceability of the common optocouplers PC817, 4N3x, 6N135-6N137, and their speed. It is based on the ATMEGA48 microcontroller, which can be replaced with ATMEGA88. The parts being tested can be connected and disconnected directly into the included tester. The test result is displayed by LEDs. The ERROR LED lights up when there are no connected optocouplers or their malfunction. If the optocoupler, when installed in its socket, turns out to be working, then the corresponding OK LED will light up. At the same time, one or more TIME LEDs corresponding to the speed will light up. So, for the slowest one, PC817, only one LED will light up - TIME PC817, corresponding to its speed. For fast 6N137, all 4 speed LEDs will be lit. If this is not the case, then the optocoupler does not correspond to this parameter. The speed scale values of PC817 - 4N3x - 6N135 - 6N137 have a ratio of 1:10:100:900.
The tester circuit for checking optocouplers is very simple:
click to enlarge
We connected the printed circuit board for power via a micro-USB connector. For the parts being tested, you can install collet or regular DIP panels. In the absence of such, we simply installed collets.
Microcontroller fuses for firmware: EXT =$FF, HIGH=$CD, LOW =$E2.
Printed circuit board (Eagle) + firmware (hex).
