(Topic ID: 157714)

Test opto out of circuit


By dri

4 years ago



Topic Stats

  • 11 posts
  • 5 Pinsiders participating
  • Latest reply 4 years ago by Pin_Guy
  • Topic is favorited by 1 Pinsider

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IR_On_(resized).jpg
IR_Test_Setup_(resized).JPG

#1 4 years ago

Is it possible to test an opto out of circuit? For the sake of the discussion lets pretend it's a TZ clock opto (it's a hyperball opto, which is similar). I can't find the optos in the HB schematics and have no clue how to rig this. I have a lab voltage supply. Is it just order new ones? (my main boards are a k's and I can't game test them at the moment)

#2 4 years ago

If it's in the game and getting power, your phone camera will show IR light.

If you mean bench test, that's different.

#3 4 years ago
Quoted from jwilson:

If you mean bench test, that's different.

I want to bench test them, but I'll just order new ones as it will be less time consuming I'd imagine.

#4 4 years ago
Quoted from dri:

I want to bench test them

The max forward voltage is 1.7v, in game they typically see around 1.5v. The photo transistor is going to be a little tougher to check, you will need to put a source voltage on the collector, and you will want to put a load resistor to ground on the emitter. To see that its on, you can add a current limiting resistor and LED to the emitter as well.

#5 4 years ago

You can make something like this for the transmitter ...

IR_Test_Setup_(resized).JPG

Without camera flash ...
IR_On_(resized).jpg

#6 4 years ago
Quoted from Pin_Guy:

You can make something like this for the transmitter ...

Thanks for putting this together. I need to start being handier with these kind of things. I took the shortcut and bought new ones.

#7 4 years ago

The key point to remember is that ANY LED will require a current limiting resistor in series with any power you connect to it or it will fry in micro seconds.

Exact value is determined by the voltage applied and the circuit in which it is used BUT a rule of thumb that is good enough for a quick bench test is 220R for 5V and 1K2 for 12V.

A 1/4 watt resistor will be adequate for most tests.

Testing the RX transistor is a little more complex as stated but they are usually quite reliable.

#8 4 years ago

I just used the resistors I had on hand; but, those are the same value/size used in the Williams 16 opto board for the transmitter load resistors.

Quoted from Homepin:

The key point to remember is that ANY LED will require a current limiting resistor in series with any power you connect to it or it will fry in micro seconds.

Not to be argumentative; but, I have to disagree with this statement as you can drive an LED with a 5V forward voltage, powered by a 5V source for a very long time. I have some that have been running 24/7 for at least 5 years like that.

#9 4 years ago
Quoted from dri:

Thanks for putting this together. I need to start being handier with these kind of things. I took the shortcut and bought new ones.

Nothing wrong with that, I usually just check the voltage drop across the LED to determine if they are on or not.

#10 4 years ago
Quoted from Pin_Guy:

Not to be argumentative; but, I have to disagree with this statement as you can drive an LED with a 5V forward voltage, powered by a 5V source for a very long time. I have some that have been running 24/7 for at least 5 years like that.

Interesting. What is the measured voltage drop across the LED? What is the measured forward current? One would suspect that the voltage source has appreciable internal resistance or that there are other relevant circuit elements (for example, two LEDs in series or an internal current limiting resisitor or an FET with significant on resistance).

#11 4 years ago

In a WPC machine there is an opto board mounted under the playfield that contains the current limiting resistors providing the necessary voltage drop. I would say 1.5V +/- 10% is a good working voltage across the LED.

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