Re: unknown circuit in a C64

Mike wrote:
Pin 1 is ground, pin 3 is reset. It looks like there is a cable
extending from the "circuit", perhaps going to a reset button?
The resistor, capacitor and diodes may be in order to prevent an
overload of some sort if the reset button is hold for too long.

--
Anders Carlsson

Anders, if you mean the 2 grey wires that go out of the picture those
are going to pins 1 & 3 on the user port, the componants in the photo
were taped to the motherboard in the open space between the rom & ram
chips and the wires went between the CIA's to the user port, that is
what is confusing the diodes are piggyback but why? if they were
opposite to each other they would cancel each other out, but they are
the same way so why 2?
and the resistor and cap are piggyback as well but go nowhere.

I wondered about a reset as well but the dead end with no external way
to use this is what puzzles me.


One of the diodes looks like it may be a Zener diode- the other, a switching diode. In a reset circuit, the capacitor/resistor combo charges, until the forward voltage exceeds the Zener's rating. It conducts, discharging the capacitor, which is probably slowed by the resistor- a one shot mulivibrator that makes a long enough reset pulse to reset the machine.

That's my $0.02.

-Urson Bear
.

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