(Topic ID: 300822)

System 11a no blanking at 1j22 and 1j21

By JT-Pinball

36 days ago

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    #1 36 days ago

    Hello all, I’m finally getting around to fixing this Road Kings I have no matter what. This is partially from an older post but most of that stuff was resolved and I’m just want to try to boil this down to the core issue. Board is on branch, with ground, 5v and +12 board boots and shows a 0 on the display. When I push the cpu diagnosis button the board flashes 8 and goes back to 0. This according to the manual and repair guide says this is normal operation and the blanking signal is working correctly. When I check the blanking at 1j3 12 I have 4.26v. As I follow this back on the schematic I see that the signal for the blanking to those pins originated from U50 pin 12. I see pin 11 and 12 on the 7402 are inputs. 11 shows high 12 shows low and pin 13 shows high. This violates the truth table for the chip. But since both are inputs? I still think u50 is dead. When I follow this back to the PIA at u10 I have the same high signal on pin 19 of u10. What’s interesting is I have no signal or voltage on pin 21. U10 dead?

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