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Main Question: How can I check a ADC0808 chip to determine if it needs to be replaced or if my issue is something else? Any advice you can offer is SO appreciated!

ADDITIONAL INFO When the arcade is in "Test Mode" (see test mode picture below for context) the output values for the X and Y axis data are not smooth and it only registers a couple of HEX values. Accordingly, it appears that the cursor\crosshair follows the behavior and moves to a different point on the screen when the HEX value changes.

X axis (VRP1X: right to left) - 0080 00C0 00E0 00F0 00F8

Y Axis (VRP1Y: top down) - 0080 00C0 00E0

enter image description here

Here is a link to the full schematics

(Overview) I am working on a Operation Thunderbolt arcade game. It has two guns (player 1 and 2) that use two 5v potentiometers (2 each gun) to send X and Y signals to a ADC0808 chip which appears to convert the analog signal to digital. The digital value is then used by the game to control the crosshairs of the guns on the screen.

(Issue) The crosshairs are way off in the upper right corner and they are not very responsive and jittery.

(Troubleshooting)

  • Found the schematics and found where the potentiometer signal is coming into the arcade PCB. I traced the signal to the ADC0808 chip (FYI: the chip on the board is actually a ADC0809N chip). I tested the VCC pin and it was 5v as expected. The input pins 26, 27, 28 and 1 and could see the voltage from the potentiometer within the 5v range. enter image description here enter image description here enter image description here

  • I put the arcade into test mode and went to the calibration screen. I could see that the X and Y values were responding. Also, while checking voltages (see #1) i noticed that the crosshair was still not behaving correctly, but jumped to an area closer to the middle of the screen enter image description here

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    You write that you "could see the voltage from the potentiometer within the 5v range", but did you actually check the full range of each pot? Can you the the voltage from the pot going to the ADC vary through a nice smooth 0-5V range as you adjust the pot? – brhans Jun 10 '20 at 22:21
  • Thanks for the quick reply brhans! I'll try to get an extra hand and provide additional feedback on the pot voltage while someone else is turning the guns while I monitor the multi-meter. I was having to wedge the gun in place and then take measurements when troubleshooting by myself. – Chuck Mathis Jun 10 '20 at 23:41
  • I did another round of voltage tests on the player 1 gun. The voltage seemed smooth when the guns were moved slowly. ADC0809N's Pin 26 ranged from 1.5 - 3.4 volts for player 1's X axis. Pin 27 ranged from .5 - 4.0 volts for player 1's Y axis. – Chuck Mathis Jun 10 '20 at 23:59
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    "The voltage seemed smooth when the guns were moved slowly" - What diagnostic readings did you get for 0.5 - 4.0V? Do you have an oscilloscope? – Bruce Abbott Jun 11 '20 at 5:29
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    It looks like someone has scribbled notes on the schematic, mostly in Korean. But I notice "N/C" on several of the data lines of the ADC0808. That could explain a few things, couldn't it? – Chromatix Jun 15 '20 at 21:18

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