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

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 . SAFETY CONSIDERATIONS
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 should be 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) The more 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 same way as
open-collector TTL outputs. Thus, they may be
wire-ANDed or wire-ORed .