Tektronix 2440, User Manual

Page: 211 / 531

Maintenance— 2440 Service
operating temperature since the last SELF CAL was done,
or hard failures caused by component problems in the
instrument’s circuitry that prevent calibration.
S o ft E rro rs
These errors appear as a loss of SELF CAL and are
noted by the UNCALD label appearing above the SELF
CAL choice in the main CAL7DIAG menu. Running the
SELF CAL routine and obtaining a PASS status clears up
any soft calibration errors and revalidates the instrument
calibration.
Hard Failures
A hard failure affecting calibration may also be indicated
by the loss of SELF CAL, but running the SELF CAL rou­
tine does not produce a PASS status for SELF CAL or
any failed test in EXT DIAG. Loss of ATTEN or external
TRIGGER calibration is noted by the UNCALD label
appearing above those choices in the EXT CAL menu. A
loss of calibration for either ATTEN or TRIGGER indicates
a possible nonvolatile memory failure. In either case,
instrument calibration should be considered void, and the
scope must be referred to a qualified service person for
servicing.
STATIC-SENSITIVE COMPONENTS
The following precautions apply when performing any
maintenance involving internal access to the instrument.
S ta tic d is c h a rg e c a n d a m a g e a n y s e m ic o n d u c to r
c o m p o n e n t in th is in s tru m e n t.
This instrument contains electrical components that are
susceptible to damage from static discharge. Table 6-1
lists the relative susceptibility of various classes of semi­
conductors. Static voltages of 1 kV to 30 kV are common
in unprotected environments.
When performing maintenance, observe the following
precautions to avoid component damage:
1. Minimize handling of static-sensitive components.
2. Transport and store static-sensitive components or
assemblies in their original containers or on a metal rail.
Label any package that contains static-sensitive com­
ponents or assemblies.
3. Discharge the static voltage from your body by
wearing a grounded antistatic wrist strap while handling
these components. Servicing static-sensitive components
or assemblies should be performed only at a static-free
work station by qualified service personnel.
4. Nothing capable of generating or holding a static
charge should be allowed on the work station surface.
5. Keep the component leads shorted together when­
ever possible.
6. Pick up components by their bodies, never by their
leads.
Table 6-1
Relative Susceptibility to
Static-Discharge Dam age
Semiconductor Classes
Relative
Susceptibility
Levels8
MOS or CM O S microcircuits or
discretes, or linear microcircuits
with MOS inputs (Most Sensitive) 1
ECL 2
Schottky signal diodes 3
Schottky TTL
4
High-frequency bipolar transistors 5
JFET 6
Linear microcircuits 7
Low-power Schottky TTL 8
TTL (Least Sensitive) 9
‘ Voltage equivalent for levels (voltage discharged from a
100 pF capacitor through a resistance of 100 ohms):
1 = 100 to 500 V 4 = 500 V 7 = 400 to 1000 V (est)
2 -= 200 to 500 V 5 = 400 to 600 V 8 = 900 V
3 - 250 V 6 = 600 to 800 V 9 = 1200 V
6-3