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Page 21
1N1UCH CAN BE EXCHANGED ONE BY ONE.
THE VECTORED INI'ERRUFT AND REAL TIME a..oCK
COMroNENrS, IC Al, ARE
I:iOT
NECESSARY IN THE BOARD AT THIS TIME AND SHOULD BE
REMOVED.
USING A SCOPE, EXAMINE THE OUTPUT PINS OF ALL CHIPS.
LCW LCGIC LEVELS
ARE NJRMALLY LESS THAN
0.2 VOLTS AND HIGH GREATER THAN 3.0 VOLTS. A LEVEL OF
0.4 VOLTS MAY INDICATE SHORI'S BE'lWEEN OUTPUTS WHERE ONE IS TRYING TO PULL HIGH
AND THE GrHER LOW.
A LEVEL OF
1.
2 VOLTS INDICATES AN OPEN CIRCUITED INPUT.
NMOS CHIPS HAVE SIMILAR LOGIC LEVELS, WHILE PMOS CHIPS CAN PULL
TI'L
INPUTS TO
-0.6V WHERE WE INPUT CLAMP DIODE LIMITS 'IRE VOLTAGE.
00 NOT BE SURPRISED AT
HOW STRANGE SOME OF THE WAVEFORMS CN THE BUS LOOK, SUCH AS THE DI LINES.
THERE
ARE PERIODS OF TIME DURING WHICH THE BUS IS
IDr
BEING ACTIVELY DRIVEN, AND THE
VOLTAGE MAY DRIFT DUE TO RECEIVER INPUT CURRENT.
ABNORMAL OPERATION IS
INDICATED PRINCIPALLY BY ABNORrJ.AL LCGIC LEVELS MAINI'AINED CONSTANT FOR AT LEAST
ONE CLOCK PERIOD (500 MICROSECONDS) •
ONCE YOUR BASIC SYSTEM IS WORKING, CHECK OUT OF MEMORY BOARDS AND OTHER
INTERFACES IS RELATIVELY STRAIGHTFOIMARD USDiG THE MEMORY TEST PROGRAM IN THE
MONITOR, OR SIMPLE DIAGNOSTIC roUTINES YOU CAN PROGRAr4 IN MEMORY ON THE PROM/RAM
BOARD.
AFTER YOUR SYSTEM IS UP AND RUNNING, IT SHOULD BE QUITE RELIABLE.
SINCE
MOST MICROCOMPUTER SYSTEMS ARE MEMORY INI'ENSlVE, THE MEMORY IS THE MOST LIKELY
SOURCE OF COMPONENr FAILURE.
A SYSTEM WITH 32K OF STATIC MEMORY MAY CONTAIN 75%
OF ITS COMPONENI'S CN THE MEMORY BOARDS.
IF A PROBLEM IS EXPERIENCED RUNNING A
PRCGRAM, FIRST SUSPECT THE MEMORY AND USE THE MONITOR TEST PR0GRAr4.
WE HAVE 'Y"ET
TO EXPERIENCE A PROBLEM WITH CUR 8K MEMORY BOARDS THAT WAS NOT REVEALED BY THE
TEST PROGRAM.
IF YOU
IX)
MUCH REARRANGniK3 OF YOUR SYSTEM, IT IS A GOOD PRACTICE
TO TEST MEMORY FOR A FEW SECONDS \·VHEN YOU FIRST TURN ON THE COMPUTER TO MAKE
SURE THE BOARDS ARE ADDRESSED PROPERLY OR THAT THEY ARE IN THE COMPUTER.
THIS
MAY SAVE SOME HEAD SCRATCHING WHEN THE PROGRAM YOU HAVE JUST LOADED FAILS TO
RESPOND TO YOUR EAGER KEYBOARD TOUCH.
IF YOU SUSPECT TEMPERATURE SENSITIVE
CHIPS, REMOVE THE COVER OF THE CCMPurER 'ill INI'ERRUPT AIR FLOW BETWEEN BOARDS.
WE 00 NOT RECOMI"1.END OBSTRUCTING THE AIR FLCW THROUGH THE COMPUTER BY PLACING A
SHEET OF PAPER OVER THE LEFT SIDE.
A FULL COMPUTER MAY DISSIPATE OVER 300 WATTS
AND REACH UNACCEPTABLE TEMPERATURES IF NO AIRFLCW IS PERMITTED.
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