| |
| Running these tests
assumes that these areas of the circuit function > |
A: The +16
volts power supply. |
| B: The audio
amplifier section. |
| To troubleshoot one of these
sections > |
<in
progress> |
| |
| Controlling
the digital sound
generation areas of the circuit: |
| |
The purpose of the interface shown below is to troubleshoot the music
and sound circuitry on a Ms Pacman PCB. It is used to place data into
the 7489 (82S25) chips located at 2K and 2L.
Because the output pins of this type of ram are not
also the input pins, it is not possible to read back data from this area
of the circuitry. In order to verify these ram chips, it becomes
necessary to view their output data with an oscilloscope. To have the
ability to clear these ram chips, and then test each output individually, is
why this interface was designed.
|
 |
| In order to provide the
required write pulses for the ram, watchdog reset, and the 8-bit
addressable latch, this control over the address decoding 7J and 7M is
built into the sound test module. |
 |
|
For the sound to be heard, pin
1 of the 74LS273 at location 2M must be turned on. This is accomplished
by controlling the 74LS259 chip at location 8K. This
process
can be turned on or off. |
 |
| This interface was designed to
write values into the music ram circuitry, without the game having to be
played.
7489 music and sound tests. Each of the 16 locations
of the 7489 chip can be programmed with any one of the 16 possible
variables, by selecting the appropriate slider bar for that
location.
Most combinations of the
slider bar adjustments yield bizarre sounding results. However, during
troubleshooting, this area of the circuitry, single pins on the 7489 IC
can be targeted and followed through using an oscilloscope. |
 |
|
For an example of the actual software used to
troubleshoot sound and music problems at GLS1 Electronics, refer to the Ms
Pacman Troubleshooting Tool page. A link is provided there to
download the module. The file is a program, which contains several
interface screens used for live in-circuit testing of IC's while
troubleshooting the Ms Pacman circuitry. It also provides other useful information
for diagnosing and solving problems found while servicing Pacman or Ms
Pacman circuit boards.
The software can also be used as a tool to
understand the operation of digital IC's, and how different sections of
the circuitry function together. Logical conditions can be introduced
and "stepped through", while examining the expected results
displayed as highs and lows on simulated LED's.
|
| All sound problems can be found and corrected, and all
boards submitted for repair will undergo these tests, providing the customer
with assurance that
all sounds will be correct during game play. |
Contact me at greg@gls1electronics.com
on how to troubleshoot different sections of the Ms Pacman circuitry, or for
Pacman repair or Ms Pacman repair.
|
