ZX Spectrum Z80 Keeps Resetting

Rob Jarratt robert.jarratt at ntlworld.com
Mon Jan 1 12:34:30 CST 2018

> -----Original Message-----
> From: Jon Elson [mailto:elson at pico-systems.com]
> Sent: 01 January 2018 18:07
> To: rob at jarratt.me.uk; Rob Jarratt <robert.jarratt at ntlworld.com>; General
> Discussion: On-Topic and Off-Topic Posts <cctalk at classiccmp.org>
> Subject: Re: ZX Spectrum Z80 Keeps Resetting
> On 01/01/2018 11:22 AM, Rob Jarratt via cctalk wrote:
> > I just replaced the last of the electrolytics, but the spikes on the
> > Z80 5V rail have not gone away. They only exist on the 5V rail in
> > close proximity to the Z80, other chips with a 5V supply don't have
> > the spikes on the 5V rail.
> >
> It could be caused by bus contention, which may also be the cause of the
> resetting.  Possibly some of the decode logic has failed, and is allowing
> devices to drive the data bus at the same time.  I've seen this before,
and it
> does cause spikes on the 5V rails.

That is interesting, I hadn't considered that. Given that it gets a fair way
into the boot sequence it would have to be an intermittent failure.



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