Hello all,

my friend has a broken tire balancing machine that we're trying to fix. The problem is with the rotation positioning of the tire. The machine measures the rotational position with 3 optical sensor and a circuit as depicted below:

Measurement circuit schema
2 out of the 3 channels work as expected, but the third channel (red net) is constantly pulled to ground, no matter of the position of the tire. We've managed to trace the problem down to the unmarked 8-pin IC, but due to the manufacturer erasing any markings on it, we are unable to search for a replacement.

Does anyone have an idea of what the mysterious component could be? Maybe a buffer before the microcontroller?

The tire balancing machine is labeled Torin Big Red, but it is probably sold under many names. Google reverse image search of the control board gave out many identical cards.

Below are a few photos of the control card and a close-up of the faulty IC (U11) on the lower right side of the board:

Close-up of the cardClose-up of U11Backside of U11
Any help is appreciated

 

Could it possibly be a 555? The inputs go to trigger, reset and threshold, and the outputs to the micro come from output and discharge. I can't think of anything else with the power on 1 and 8. The connection to pin 5 is harder to explain.
The micro is an 8051 or an ATMEGA judging by the position of the crystal.

 

Several 8 pin PIC chips, like the 12F683, have VDD on pin 1 and Gnd on pin 8.

Thus, if I allowed to guess, it is a Microchip microcontroller.
And this is ONLY A GUESS. Don’t become upset at me.

 

A suggestion,
U13 above this chip, is labeled 4024, which is probably a cd4024 cmos counter.
I'm wondering if under this chip there is a number printed,

 

I know the ground pin is wrong but I think something like this.

I looked at 400 buffers, inverters and Schmitt but none had pin1=gnd.
I see why Schmitt Trigger thinks it is a 12Fxxx.

 

A suggestion,
U13 above this chip, is labeled 4024, which is probably a cd4024 cmos counter.
I'm wondering if under this chip there is a number printed,

Good observation.

@Naabi, if you know that that IC is faulty (and how did you determine that the problem isn't with U2's output failing as a short?), you need to remove it anyway, so see if there's a number under it.

 

and how did you determine that the problem isn't with U2's output failing as a short

I would test the IC like it is a 3x inverter or buffer.
Test to see of pins 2,4,6 are near 5V.
Test to see of pins 3,5,7 are at 0V or 5V.
Short out pin 3,4 on U1, 2 or 3 and see of one of the output pins changes state.

 

Agree with schmitt trigger the chip is a micro. I use several different 8 pin pic chips and the power pins are 1=+ Vcc, 8= Gnd.
If actually defective then probably SOL