HP 9845B/C CE Handbook page 55

9845B/C
Mainframe Troubleshooting 4-11
Memory Troubleshooting
Memory errors in the read/write memory tests or the ROM checksum test can be translated to give
the physical location of the memory error. Generally mUltiple failures indicate that the memory
control logic is defective.
ReadIWrite Memory Errors
ReadlWrite memory errors are displayed slightly different for the two RAM boards used in the HP
9845B/C computer. The display will be in one of the following forms:
a. For the 128k byte RAM board (HP pin 09845-66526):
MEMORY ERROR BLOCK 04 ADDRESS 002052 HAS 000400 NOT 000000 or
..
..
..
. .
b. For the 512k byte RAM board (HP pin 09845-66590):
MEMORY ERROR BLOCK 24 ADDRESS 002052 HAS 000400 NOT 000000
..
..
..
..
Block Octal
Actual Expected
(Octal) Word
Octal Octal
Address Data
Data
1. First determine which memory assembly contains the block indicated in the error display.
Refer to the following Figure for help:
Press this side for
LSB
rnB
MSB
JmB
0-------0
0----0
0----0
Block Select Configuration Switches
09845-66526
0 0
BLOCK 14 and 16
BLOCK 10 and 12
BLOCK" and 6
BLOCK 0 and 2
(Do not use)
Blocks
20-36
40-56
60-76
128K byte Boards 512K byte Boards
Block Select Settings
MEMORY ERROR BLOCK 04 ADDRESS 002052 HAS 000400 NOT 000000
..
2. This digit of the octal word address indicates either the upper half (high address) or the lower
half (low address) of a block. Note that this information is not needed for the 512K board.
The Block information is enough to locate the row of
Ie
chips.
a. If this digit is 0 through 3, the low address is indicated.
b. If this digit is 4 through 7, the high address is indicated.
3. Decode the data into binary values and compare the bits:
a. Actual Data
0 000 000 100 000 000
b. Expected Data 0 000 000 000 000 000
A
4. The bits that do not compare indicate a defective RAM location. The follOwing U1ustrations
show the RAM chips that correspond to each bit position.
09845-90039. new
page:
4184
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