NorthStar HORIZON Manual page 51

G2. This step will check the write circuitry while simulating
writing a continuous stream of "one" data bits in single-
(lensity format during each sector.
A. With the computer power off, remove the disk controller
Iloard from the motherboard.
B. Eemove the 74LS74 IC from location 14C, bend out pin 9 of
I:he IC, and re-insert the IC so that pin 9 is outside the IC
'locket and does not make contact with IC socket pin 9.
C. Connect
pin 30.
''lire on
148 pin
a clip lead between cable connector (J2) pin 22 and
If you do not have a clip lead, then tack solder a
the solder side of the board between 138 pin 11 and
13 .
o.
I~ith
the computer power off, install only the disk
I:ontroller board and the processor board into the
motherboard, and turn the ,computer power on.
E. ':heck the following signals while the computer reset switch
is depres'led (hold depressed with a rubber band):
:3IGNAL LOCATION DESCRIPTION
I~R-SHIFT/ 60 pin 6 AC, (-Ius, Bus)·
~D-WSR/
60 pln 15 AC, (-Bus,64u's)
I~S7
50 pin 13 AC, (-'-96us,32ms)
1.
e. mostly HIGH
I~S10
5C pin 15 AC,
(-96us,32ms)
1.
e . mostly HIGH
I,RITE PULSE 3C pln 5 AC, (+approx 600-700ns,4us)
(no name)
3C pin 13
AC,
(+approx 600-700ns,4us)
".EAD DATA
148 pln 12 AC,
(+approx 500-700ns,4us)
If
the signals are not as listed then refer to the schematic
,lrawings and trace backwards to locate and correct the
)roblem.
G3. rhis step will check the read circuitry while simulating
reading
c
continuous stream of zero" data bits in double-
density format during each sector. If using a scope to
:heck signals then sync positive on 13C pin 9. Continue
~ith
the same setup as
i~
the previous step. Check the
following signals while the computer reset switch is
depressed.
SIGNAL
WINDOW
RE
ACQUIRE
51
LOCATION DESCRIPTION
13C pln
9
"Window" ,
HIGH for 96us then LOW
58 pln 6
" Read Enable
ll
,
goes HIGH at 430us
SA pin 5
"Acquire Phase of Incoming Signal" ,
goes HIGH with RE, duration 100-150us
North Star HORIZON Computer