Troubleshooting - Testing The CR8 (Optocoupler)
HINT: These components die with age. If you have an older VideoCipher board
then there's a good chance this needs replacing or will need replacing in
the next while.
CR8 - Is an optocoupler
WHAT IS AN OPTOCOUPLER?
An optocoupler is a device that totally isolates an input circuit and an output circuit. The most common use is protection from high-voltage transients, surge voltage, or low-level noise that could possibly result in an erraneous output or damage the device.
Optocouplers also allow interfacing other circuits with different voltage levels.
* Photo Courtesy of BUZZ, thanx man! *
The input circuit of an optocoupler is an LED, the output is a phototransistor as seen above.
When the LED is on there is current flowing through the phototransistor, when the LED is off then no current is flowing through the phototransistor and the component is in it's off state. Optocouplers usuall turn on and off thousands of times per second.
ok enough theory, now lets fix the damn thing :)
TESTING AN OPTOCOUPLER
In order to test CR-8 you MUST remove the component from the circuit board.
You will need the following to test an optocoupler:
A Variable DC power source (A 9 volt battery with a potentiometer will do fine)
- 1 Kohm resistor ( This is a current limiting resistor for the internal LED)
- 1 Kohm Potentiometer (Not Needed if you have a variable DC power supply)
- DMM (Digital Multi-meter)
0. Measure the resistance of your potentiometer and set it to 0 ohms
1. Hook up the circuit as follows:
- hook the NEGATIVE terminal of your power supply to the negative terminal of the optocoupler, this would be the side marked LED and a minus (-) sign
- hook one of the outside legs of the potentiometer the negative terminal of the battery
- hook the other outside leg of the potentiometer to the positive terminal of the battery
- wire the center leg of the potentiometer to one side of the 1Kohm resister
- the other side of the 1kohm resistor should be conencted to the (+) LED side of the optocoupler
2. Place your ohm meter across the opposite side of the optocoupler, polarity does not matter when measuring resistance
3. Start with the voltage on the wiper (center leg) at 0 volts and slowly increase, watching your ohm meter the higher your voltage gets the the smaller the value of resistance will be:
EG: at 9 volts on the wiper I got a resistance value of about 1.15 kohm's across the optocoupler
!!! WARNING !!!
Do not turn your voltage too high as you can cause damage to the CR8
If you vary the voltage and still get infinite ohms or out of range values then your CR8 is defective and should be replaced
* Your resistance value at around 9 volts should be in the kilohms, if higher CR8 is defective or becoming defective and should be replaced *
I have tried this and works like a charm :) one of my own test circuits to help people with possible CR8 problems hope it makes yer lives easier hehe considering some problems are blamed on CR8 but CR8 is not always the real problem
use this method to test for a bad CR8, if this method turns out that the CR8 is good then look elsewhere for the problem.
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