Z80 / Z84C Swap (Doh!)

Sean Caron scaron at umich.edu
Mon Aug 17 12:40:39 CDT 2015

You should be able to get a replacement NMOS Z80 from Jameco for four or
five bucks ... if you put a 5V CMOS Z80 in there, I wouldn't expect it to
really hurt anything; it might not run exactly right depending on
tolerances in the system design I would suspect mostly due to (a) logic
threshold differences and (b) fan-out differences especially given one
logic family driving another ... but I wouldn't expect it to really damage

I have a mostly working Executive ... logic is OK but the screen will roll
when the environmental conditions are just right (probably some caps are
getting dodgy, or a cold solder joint) ... it's usable ... I have all the
original media and documentation; plenty of bootable floppies; I've got a
sleeve of 5.25" blanks and I could run off a few duplicates for you ... not
sure if these will work on the Osborne 1 ... if you're in the USA and you
want to give some of the media from the Executive a shot, maybe I could
help you out.



On Mon, Aug 17, 2015 at 1:48 AM, drlegendre . <drlegendre at gmail.com> wrote:

> Thanks for the input, gents..
> Sigh.. and here I sit, yet again, with neither a logic analyzer nor a
> decent digital scope. Unless something comes up, looks like I'll have to do
> it the hard way, as usual - heh.
> At least the machine doesn't have a totally scrambled brain, with the
> correct CPU - so it will be easier to work through things, as I can at
> least partially communicate with the hardware if needed. Well, except for
> the lack of bootable media..
> Anyone have a spare Z-80? Or some bootable media for the Osborne 1? I have
> a few CP/M machines here, but I don't think any of them can write media for
> the Osborne. Even so, I'd need a way to get the Oz disk images to the
> machine of choice.. and that's another huge hurdle.
> Help a brother out.. I need some bootstrap media!! ;-)
> On Mon, Aug 17, 2015 at 12:13 AM, tony duell <ard at p850ug1.demon.co.uk>
> wrote:
> > [Replacement Z80 in an Osborne]
> >
> >
> > > What I did learn is that Z-80 were made in CMOS versions, and the Z84C
> is
> > > one.
> > >
> > > So what did I most likely do, here? Hose the CPU for sure? Collateral
> > > damage on the board? Both / Neither?
> >
> > Most likely neither (unless you put the CPU in the wrong way round or
> > zapped
> > something with static -- CMOS _and_ NMOS parts can be damaged that way).
> >
> > If the CPU is fast enough for the clock speed in that machine then most
> > likely
> > a CMOS one will work without problems.
> >
> > My guess is that the missing CPU was not the only fault. You now have a
> > good
> > CPU but problems elsewhere (clock, ROM, RAM, support logic...). Time to
> > grab
> > the logic analyser :-)
> >
> > -tony
> >

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