Re: Franklin Ace 1200 -odd little jumper

["Michael J. Mahon" <mjmahon@aol.com>]

Ernest wrote:
> There is a little jumper wire on my Franklin Ace 1200 motherboard, and I
> have no idea what it is for. Here is a picture of it:
>
> http://www.apple2clones.com/images/jumper-981.jpg
>
> Does anyone know what this odd little jumper/short is for?
>
> Here is a sketch of where the wires go to, with the chip type listed next to
> it:
>
> http://www.apple2clones.com/images/chips2-982.jpg
>
> I don't know what the pin numbers are but...
>
> If you hold the SN74LS20N chip with the notch facing left, the wire connects
> to the second pin from the left on the top.
>
> If you hold the SN74LS08N chip with the notch to to left, the wire connects
> to the sixth pin from the left on the top.
>
> I'm not sure what these two chips are for, but I've run the computer with
> the wire plugged in and out, and I can't see any difference in how the
> system performs.
>
> Any guesses as to what this jumper is for?

I think we can figure this out with a couple more pieces of information:

1) the location numbers of the two chips mentioned above (on the main board)
2) the schematic, which should have the gates labelled with the location
   numbers, and, hopefully, with pin numbers.

The pins of DIP chips are numbered consecutively, going around the
chip, starting with "pin 1" as the pin nearest the dot on the top of the
plastic case.  If  no dot is visible, then, if you look down on the chip
with the "notch" facing left (as they are in your photos), then pin 1 is
the leftmost pin on the bottom.  So the numbers on a 14-pin DIP run:

14 13 12 11 10  9  8

(notch)

1  2  3  4  5  6  7

From your description, it sounds like the wires go to
pin 9 of the 74LS08 and pin 13 of the 74LS20.

Both of these pins are inputs to gates, so the wires must
continue to other IC's, one of which drives the wire.

The location number (e.g. H1, for the 74LS08, since it is
in column H, row 1 (I think)) should appear next to the
corresponding gates on the schematic.  The 74LS20 seems
to be in location F6.

The 74LS08 has four 2-input AND gates in one package, so its
location number should occur next to four gates, with different
pin numbers next to the gate inputs and output.  The 74LS20
is a dual 4-input NAND gate, so its location number should
appear next to two gates.

Does your schematic have this information?

-michael

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Home page:  http://members.aol.com/MJMahon/