On Fri, Sep 29, 2017 at 4:20 AM, Francesco Messineo <francesco.messineo@gmail.com> wrote: >> I will also change the timing resistor and tantalum capacitor on the >> 555 reset circuit, I've noticed the reset signal isn't very well >> behaved (it resets randomly and sometimes doesn't release the reset >> line). I think the tantalum capacitor is shorting randomly to ground >> or the 1M resistor is intermittent. It _should_ be a ceramic cap there (not all hard-shell shiny caps are tantalums) but if it's a large value and electrolytic, it's probably a tantalum. I'd be less worried about the resistor failing, but that's an easy test. Either way 555-based reset circuits do age poorly. > update: changing the UD8 socket, did bring the system to the basic > prompt, with correct bytes free count. Nice. Yes. Multiple bad sockets - not surprising. > I then restored the two CAS resistors (I had lifted them to swap RAM > banks) and now I have a completely black screen, not even the garbage > screen if I remove the UD9 ROM :( Hmm... that's really odd. > Looks like I now have to debug the video signal path. Yep. Check Φ2. I am pretty sure you don't get video if the CPU is not installed and cranking Φ2 out. Maybe you also have a bad CPU socket? You don't have to be running good code - which is why you get random chars when the KERNEL ROM us pulled, but you _do_ have to have something generating Φ2 to feed into the video circuit. It's also possible something failed in the primary timing circuit? Rather than bad/missing output from CPU, the input clock is bad? -ethan Message was sent through the cbm-hackers mailing listReceived on 2017-09-29 18:00:03
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