Re: Tech: Tempest (not)reset line & WD

From: Mark Shostak <xx.vl_at_cinelabs.com>
Date: Thu Apr 01 2004 - 23:35:23 EST

Roger,

On Thu, Apr 01, 2004 at 10:03:11PM -0600, Roger Smith wrote:
> Around what voltage level should the (not)reset line be at normally and when
> the reset button is pressed?

When reset is pressed, the !reset signal should be close to (not)zero volts.
Technically, anything <.75V is fine. When the button is released and everything
is working, !reset should be close to 5V.

> Also, I am trying to figure out how to use the disabled watchdog as a tool
> when troubleshooting. When I'm looking at the faulty (not)reset circuit with
> my logic probe, and the WD is NOT grounded, the entire circuit is barking.

Sounds good.

> When the WD IS grounded, the circuit is at the correct logic levels for the
> most part, with only a small area barking. If I understand correctly,
> grounding the WD makes the program run properly for the sake of

Not exactly. Grounding the WD disable signal only stops the watchdog from
reseting the CPU and the reset of the board (VSM, etc.). It can't make the
program run properly, if, say, you have a bad ram, or a bad rom.

> troubleshooting, so I'm guessing the area that is still barking even with
> the WD disabled is the faulty part of the circuit.

I'm not sure what you mean by "area". The only area of the WD circuit you
should care about, is the output, and to a lesser extent, the input.

> Am I interpreting this correctly? If not, could someone please clear this
> up for me? Thanks.

Not sure what your actual symptoms are (other than a pulsing reset line).
Have you checked your ram?
Have you checked your rom?
RAM is a common failure, and the cheap sockets on that board give
intermittent rom failures.
Of course, be sure to reflow the cracked solder joints on the mathbox
harness (both ends).
Does it self test?
Any picture?

A pulsing watchdog is a common symptom. Search the archives at vectorlist.org.

> Roger

-Mark

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Received on Thu Apr 1 23:45:33 2004

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