Need help with an Atari Pong board

Thanks everybody for helping me with I,Robot. As soon as I get the
new parts in next week I will respond with an update.

I'm also working on a Pong board. I fixed the power supply circuit
and the clock circuit. I'm stumped with the horizontal counter
circuit.

I will refer to Dan Boris's excellent re-drawing of the Pong
schematic here. http://www.atarihq.com/danb/files/PongSchematic.pdf
[1]

(He gives a nice description of the horizontal counter circuit here -
http://www.atariage.com/forums/index.php?automodule=blog&blogid=52&&st=25
[2] )

1) I've carefully replaced all of the IC's in this circuit and
inspected all the traces.

2) The Problem starts with F8 (7493) which is a 4-bit binary counter.
 Both the Master Rest Inputs are low (Pins 2 and 3) so it should be
couting. The clock on pin 14 looks good to me. However I'm not
seeing any pulses on the output pins 12, 9, 4, and 11. Each of the
output pins have slightly different voltages between 1.5 to 3.5. No
clock
signal though.

I replaced the 7493 IC's with new 74L93 IC's (Not 74LS93). It's
such a simple circuit - I don't really know what else to check. I
might add that when I first got the board, the +5v pull up resistor
(normally soldered to the back of the board with a 250uf capacitor)
was blown. Probably due to a voltage regulator failure - I have since
fixed the power supply and replaced the resistor with a new 4.7k
resistor. I wasn't sure what value was in there before since it was
burnt.

Looking for suggestions. :)

Thanks!

Matt

Links:
------
[1] http://www.atarihq.com/danb/files/PongSchematic.pdf
[2]
http://www.atariage.com/forums/index.php?automodule=blog&blogid=52&&st=25

---------------------------------------------------------------------------
** Unsubscribe, subscribe, or view the archives at http://www.vectorlist.org
** Please direct other questions, comments, or problems to chris@westnet.com
Received on Sat Jul 19 15:39:26 2008