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Page 19
8K MEMORY USERS GUIDE
HOW TO LCX:ATE BAD MEMORY CHIPS
DEFECTS IN MEMORY COMPONENTS CAN REVEAL THEMSELVES EITHER WHEN THE BOARD IS
FIRST TESTED, OR AFTER HOURS OF OPERATION.
THERMALLY INTERMITTENT PROBLEMS MAY
OCCUR WHEN THE BOARD IS HOT, OR ONLY WHEN THE SYSTEM IS FIRST TURNED ON.
DEFECTS IN THE ON CHIP ADDRESS DECODERS OR ADJACENT MEMORY CELLS CAN OCCUR SUCH
THAT EACH MEMORY LOCATION APPEARS
'ill
ViORK PROPERLY WHEN TESTED BY ITSELF, BUT
WRITING IN ANOTHER MEMORY LOCATION WILL CAUSE IT
'ill
CHANGE.
INPUT SHORl'S MAY
CAUSE CNE BAD CHIP
'ill
DISABLE 'IRE ENTIRE BOARD.
m1ALL BLOCKS OF MEMORY THAT
TEST BAD IN ONLY ONE BIT CAN BE READILY ISOLATED WITH THE FOLLOw""I:NG CHART.
80
40
20
10
08
04
02
01
0000
0400
0800
OCOO
><
1000
1400
1800
1COO
~starting
addresses if board is addressed at 0000
D
D
o
D
RUN 'IRE MACHINE LANGUAGE MEMORY TEST POClGRAM WITH THE BOARD ADDRESSED AT SOME
CONVENIENT LOCATION SUCH AS 2000, OR IF YOU HAVE THE VECTOR 1 MONITOR, TYPE T
2000 3FFF.
IF ERRORS ARE DETECTED, 'IHEY WILL BE PRINTED CUT IN A FEW SECONDS.
BY WAY OF EXAMPLE, ASSUME THE FOLLCMI:NG IS OBTAINED:
*
T 2000 3FFF
2C02
47
87
2C04
D3
93
2D05
13
53
2E08
89
C9
2F15
32
72
ALL OF 'IRESE LOCATIONS ARE IN 'IRE SAME lK BLOCK, 'IRE FDURI'H row OF CHI PS ON THE
DIAGRAM, SINCE THE BOARD ADDRESS IS 2000. IT IS ALSO APPARENT THAT THE ABSOLUTE
DIFFERENCE BETWEEN THE NUMBER WRITTEN INTO MEMORY AND THAT READ FROM MEMORY IS
40 HEX.
THIS MEANS THE DEFECTIVE CHIP IS IN THE COLUMN OF CHIPS LABELED 40 AS
INDICATED BY 'IRE X.
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