Re: Mockingboard Schematic in GIF form

["a" <a@aol.com>]

"Michael J. Mahon" <mjmahon@aol.com> wrote in message
20040822192357.12124.00003851@mb-m01.aol.com">news:20040822192357.12124.00003851@mb-m01.aol.com...
> Bill Garber wrote:
>
> >"Bill Garber" <willy46pa@comcast DOT net> wrote in message
> >QPKdnX7iDI_hILrcRVn-iA@comcast.com">news:QPKdnX7iDI_hILrcRVn-iA@comcast.com...
> >:
> >: Here is one for you to do. Enjoy!
> >:
> >: http://garberstreet.netfirms.com/Mockingboard_Schematic.gif
> >:
> >: Feel free to download it. It's linked to the Downloads page.
> >
> >A small error was pointed out and was repaired. Thanks Michael.
>
> You're welcome, Bill--here are the details as you requested:
>
> : One note--the component you show as crystal X1 is actually
> : a capacitor.  I believe its value is 5pf, which, with the 4.7k
> : resistor, causes about a 25ns delay in the Phase 0 signal.
> : (The "K" suffix on the "5" indicates +/-10%.)
>
> -michael
>

Bill and Michael,
this is a great help.  However, I'm confused over the part of the
schematic that I'm most interested.

If you take a look at your schematic it appears that the output
at pin 12 of U5 is directly wired to the input at pin 11 of U5.
It would seem that this would bypass the middle inverter.
Also, is it correct to read your schematic as having the +5V
tied to pin 14 of U5 and it is not directly tied to R1 and R2?
I read it this way since there is not a dot at the intersection
just below the +5V flag.

Now, a previous thread "Apple II mistery card..." had the
following link:
http://apple2.org.za/gswv/a2zine/Docs/MockingboardSchematic.jpg
It shows that (like yours) there are three inverters in series with
a cap straddling the inner one.  But, the arrangement of the resistors
is a little different.  In this case, it appears that the resistors
are pullup on either side of the cap.

I need to admit that I'm an electronics novice.  So, I'm not
trying to point out errors - just understand and learn before
I fire up the soldering iron.

If you have the time, could you check this other drawing and
help me clarify the arrangement of this delay circuit.

If you have an actual mocking board, a good close up photo
of both sides might help too.

I really appreciate this discussion and hope to hear from
you (both).

thanks again