Re[2]: Tech: Tempest (not)reset line & WD

-----Original Message-----
From: "Roger Smith" <whooshdoo@hotmail.com>
To: vectorlist@vectorlist.org
Date: Fri, 02 Apr 2004 19:44:08 -0600
Subject: Re: VECTOR: Tech: Tempest (not)reset line & WD

>
> Hi Mark. Thanks for the info. Are the (not)reset circuit and the watchdog
> circuit the same thing? Looking at the schematics I can't figure out where
> the output is located, or the input for that matter. The game does not play,
> there is no self-test or picture, the player select button LEDs do not light
> up, and the (not)reset signal works except for a section of the circuit that
> is dead. To be specific, pins 9 and 15 of E4, pins 12 and 13 of E3, and pin
> 3 of D3 are all pulsing with the WD grounded. Other than that, the signal
> works fine in the other sections of the circuit.
>
> I've still got alot to learn, but I want to see if I can repair this myself.
> Basically, I looked over the schematics and pinpointed every place that was
> labeled as (not)reset. From what I could tell, this included the
> aforementioned chips along with A4, pin V of the Main edge conn., pin F of
> the Aux edge conn., and and J3 and H4 on the Aux board. I replaced all the
> chips and checked all the traces but nothing has changed. I'm baffled!
>
> Any ideas? Thanks again!
>
> Roger
>
here is a generic description of watchdog for you,

a timer counts up or down, if it reaches it's ultimate end it trips the reset line.

the game regularly resets the timer *before* it can reach the end, thereby preventing the reset.
if you look at the counter-reset line you will see how a specific game keeps it running.
some use address lines, some use a specific memory address or i/o pin.

the basic idea is that if the hardware cant run properly the counter times out and resets the game.

if you look at how the counter is reset and follow it back it may help you work out whats not running.

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Received on Sat Apr 3 04:21:49 2004