Bowling foul detector

[RyanG]

On one of the modules I get 1.1v at pins 5 and 6 and pin 2 is 750mV and pin 3 is ~500mV. On the other module 5 and 6 are at 8.75v, pin 2 is 9.5v, and pin 3 is 9.1v. The photodiode on the one with the high voltages is pretty warm, but not hot. It tests good with a multimeter with a voltage drop of about 0.46v which matches the other one. I checked the resistance of each resistor with a meter and they read what you would expect on both sides and they matched close enough to be within tolerance of the resistors. I wish I had a good one to compare to.

[james_s]

I wouldn't expect a photodiode to get warm, does the voltage across it change depending on the amount of light exposure? Do you have another photodiode you can try? It doesn't have to be an exact replacement, pretty much any photodiode ought to work for testing.

[RyanG]

The voltage doesn't seem to change between darkness and direct sunlight. I do have some other 2 pin IR photodiodes but I don't get how there is 9v at D2(the photodiode) anyways. One side is connected to the voltage divider to get the 1.1v and the other side is connected to an opamp input. I would think it has to be something wrong with the opamp. Maybe V+ is shorted to the inputs since everything reads around 9v on that opamp? Even if that is the case it doesn't really explain why the other one doesn't work when the voltages on that one are what they should be.

[floobydust]

I say the op-amp is shorted for the sensor with the high voltage readings at pin 5,6. The photo-diode is surrounded by high value resistors and normally there is not enough current available to warm it. The op-amp's inputs are probably shorted to power.

For the second sensor board, what is the output voltage (pin 7)? The voltage seems a little bit low on pins 1,2,3.

[RyanG]

The 2nd board has voltage of 750mV on pin 1 and 2. Pin 3 is around 500mV. Pin 7 is 47mV. Pin 5 is 1.1v. Pin 6 is 800mV.

[floobydust]

For the second sensor, I think the dual op-amp IC has also failed.
The op-amp output at pin 7 is not coming up. I think it should, as (+) input 1.1V and (-) input 0.8V, so I think the IC is bad or there is a short on the output line, if it's connected to the main board. Also the second section (+) input pin 3 0.5V and (-) input pin 2 0.75V, and output 0.75V so not working as a voltage follower. Pin 3 and 2 should be very close to the same voltage if that op-amp is working.

I'd cut all the IC's pins to get it out and then use a soldering iron to wipe off the remaining leads and clean up the pads.

[RyanG]

I guess it would make sense for both of those to be no good since the quad opamp went bad with the higher voltage before. If the V+ went up to the 18v when I hooked it up then they are probably bad, which it probably did because they run from the 12v supply that was having problems.

[RyanG]

I got the opamps in for each of the IR modules. I replaced them and everything works great. Thanks for all the help.

[floobydust]

Hey that's great news. It was a lot of work.
Any other hassles and the trimpots may need adjusting.

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