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How can I find out if the CNY70's receiver is fried?

The other day I was trying to reprogram my old bot's line follower and I think I have a CNY70 (http://www.vishay.com/docs/83751/cny70.pdf) that is fried.

The line follower schematics is http://www.adrirobot.it/robot_deagostini/line_follower/line_follower.htm (Fascicolo n°49) and the program I used is described in Fascicolo n°57

The problem is that 1 of the CNY's in the program is always showing that is has a line under it even if it has none. The others work fine. Is there a way to check if the CNY's receiver part is fried?


P.S.: all five IR led light up. checked with my mobiles camera.

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You can troubleshoot like so;

1) Look at the module through a camera ( cellphone cam or handheld one). IR light shows up purple on camera. If the light is there you know the problem is in the receiver. You already did this step.

2) To troubleshoot the receiver cover the emitter with tape and measure the resistance of the receiver with a multimeter. Shine light on it with a flashlight or another IR light source. If the resistance changes drastically (at least two orders of magnitude) then the receiver works.

3) Other than that inspect your soldering for shorts or missing connections. Appearing to always be on is characteristic of an collector that is not receiving power.

Thanks for the answer.

Test results:
1) step already done. all 5 CNY LEDs shine just fine.
2) didn't troubleshoot it exactly this way. I changed the program to have only the CNY in question always on and connected it to my multimeter and check for the output voltages with and without black line under it. The results were bad. With and without the line the CNY returned almost 4.8V. All the others returned 2.8V (no line) or 3.6V (with line).
3) the board came presoldered. I wouldn't have thought of checking it.

I don't know why, bu after step 2 I thought of swapping the position on the board of 2 CNYs (one the suspect one and the one next to it) and ... the "fried" CNY started working just fine. Didn't changed it back to its starting position. I'm going to leave it this way now that all 5 are working ok.


I think you can hook it up to an oscilator??