Re: option ROM into a 3032

From: Francesco Messineo <>
Date: Fri, 29 Sep 2017 19:30:23 +0200
Message-ID: <>
On Fri, Sep 29, 2017 at 7:19 PM, Ethan Dicks <> wrote:
> On Fri, Sep 29, 2017 at 4:20 AM, Francesco Messineo
> <> 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.

it was a 1uF tantalum capacitor and it's now a ceramic one. Reset
worked flawlessly since the substitution. The 1M resistor was good
enough and I left it alone.

> 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?

I've checked the main clock input to the CPU and it's there. I will
check the clock output and the video and sync signals going to the
monitor too. I just need to find the next free time to do it.


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Received on 2017-09-29 18:03:09

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