HP 54501A - Section 6. Service; Introduction; Safety Considerations; Logic Convention

6-'1 .
INTRODUCTION
This section provides troubleshooting,
service,
and repair informationfor
the HP 54501A
Digitizing Oscilloscope .
Troubleshooting con-
sists of flowcharts, selt
test descriptions and
instructions for use,
and signal level tables .
The troubleshooting
information is provided to
isolate a
faulty module . When a faulty module
has been located,
the disassembly/assembly
procedures help
direct replacement of the
module .
6-2
. SAFETYCONSIDERATIONS
Read
the Safety Summary at
the front
of
this
manual before servicing the
instrument . Before
performing any
procedure, review it for cau-
tions and
warnings .
WARNING
Maintenance should be
performed by
trained service
personnel aware of the
hazards
involved (for example, fire and
electric
shock) . When maintenance can
be
performed without power applied, the
power
shouldbe removed
from
the
in-
strument .
6-3 .
LOGIC CONVENTION
Where
logic levels are used in this manual,
certain
conventions are used . Logic states are
defined as
follows :
0
False, negated, inactive, or unas-
serted state .
True, active, or asserted state .
HP 54501A SERVICE
SECTION 6
SERVICE
Voltage levels representing logic states are as
follows :
LOW (L)

Themore negative of two voltage
levels .
HIGH
(H)

The more positive of two voltage
levels .
Signals may be either
HIGH
true, or LOW true .
The
HP
54501A
contains both TTL and ECL
ICs . Worst
case voltage levels for
troubleshooting and signature analysis are as
follows (IC data sheet specifications may be
more accurate) :
TTL
VOLTAGE LEVELS
Level

Voltage
LOW

less than 0 .8 V
HIGH

greater than 2 .0 V
ECL VOLTAGE LEVELS
Level

Voltage
LOW

less
than -1
.50
V
HIGH

greater than -1* .10 V
Because
ECL inputs are pulled down inside
the
IC,
an unconnected ECL input is low .
ECL
outputs may be tied together the sameway
as
open-collector TTL outputs . Thus, they may
be
wire-ANDed or wire-ORed .