Re: option ROM into a 3032

From: Ethan Dicks <>
Date: Fri, 29 Sep 2017 13:19:54 -0400
Message-ID: <>
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.

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.


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?


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Received on 2017-09-29 18:00:03

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