M68000 CPU halt on power up

Hi guys,

I'm fixing up an F-1 Dream PCB. After replacing a few 74x chips that were bad, I was poking around the 68K when I shorted the reset pin and the game came right up. Did some more testing and found that when I apply power, the 68K starts up in /HALT until I reset it via the /RESET pin and then it comes out of halt and started up.

Wondering if anyone would know off hand why the 68K would start up in halt?

That would mean the reset circuit isn't working. Usually when you power on a board with a 68k it will trip the reset as soon as it's powered on then everything boots up. If you probe the reset pin and it isn't activating low for a split second then the reset circuit isn't working.

Like James said it's a reset circuit problem. /Reset and /Halt will often share the same buffer input. (7407 or similar open collector buffer)

Thanks guys. Found a capacitor missing on the input of that 7407 so I suppose the RC time constant was 0! Popped a 10uF in there and she's alive again.