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Thread: Sprint 2 /Indy 2 Repair Log newbie

  1. #11
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    Quote Originally Posted by BorntoFly View Post
    I'm still concerned about the high on PIN 40. A logic probe shows RED but on osciliscope, it looks like a floating or weak signal? Any thoughts would be greatly appreciated.
    Until you get video the watchdog will bark. It’s how the board works

  2. #12
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    Quote Originally Posted by BorntoFly View Post
    Great. thank-you for this advise. I was using the Fluke incorrectly. (Noob). The VBLANK*, /VBLANK*, VRESET, VBLANK, or VSYNC all appear to be showing correct signals. And I can read the ROMs.
    Then those 2 PROMs should be fine.

    Quote Originally Posted by BorntoFly View Post
    I've ordered some new RAM, could the 0000- 07ff at bit 7 error cause no boot?
    Yes. Since you can read the ROMs OK, your data bus overall (/DBUS0-7) should be fine. Focus on the RAM at K3 (/DBUS7 input and the output going through the 74LS04 at J5 - pins 5 and 6 then through the LS367 at pins 6 and 7 to the data bus)

    Quote Originally Posted by BorntoFly View Post
    I'm still concerned about the high on PIN 40. A logic probe shows RED but on osciliscope, it looks like a floating or weak signal? Any thoughts would be greatly appreciated.
    If you're referring to pin 40, the CPU, you need to be concerned with the transition from low to high. the /RESET signal is active low - which is what the bar over the signal name means. It should stay low for at least 50ms when powering on the system the go and stay high when running normally. If the /RESET signal is pulsing repeatedly then the CPU cannot boot and the system is repeatedly activating the /RESET signal by means of a watchdog timer. This timer gets reset repeatedly by the CPU when it is running normally. You only see it in action when the CPU can't reset the timer and the timer hits its mark then resets the CPU.

  3. #13
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    Nice work. Clearly your approach is the way to go... my approach was logic probe/ttl based as my budget was about a third of yours. A lot of hair was pulled too!
    Hope you smash it soon! Good luck!

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