Tektronix 11A52 Service Manual page 85

Insert on page 4-17 of 11A52* manual and similarly on 11A34 (pg 4-11), 11A32, and 11A33
manuals:
Note: Although specific data about extended diagnostic routines may be obtained through the use of
EXPLAINCAL, trouble shooting a defective instrument is most easily performed using normal trouble
shooting techniquesin corifunction with the EXPLAINCAL ..
In rare instances, trouble shooting may be performed by installing default calibration constants
(ca/constants) and observing amplifier performance. The reason for installing default cal constants is that
the calibration process will otherwise attempt to cover up amplifier faults. Except for de balance
errors(generally less than J 5m
V)
and gain errors (usually less than 2%), the amplifier will behave quite
normally with default ca/constants.
For example, suppose the STEP GAIN diagnostic shows a failure. Operating the amplifier with
default calconstants will show which M377 step gain or combination of step gains are at fault when a
calibrated test signal is applied to the input. From these observation_s it is
possible to logically diagnose
signal path problems. Again, this can usually be discovered through normal trouble shooting techniques
without installing default calconstants.
Uncorrected de balance errors may place the trace off screen at lmV or 2mV/div in even a correctly
operating amplifier, but the DC Offset control may be used to restore the trace to the screen area.
Default calconstants are installed by the following procedure:
1.
Set the oscilloscope ON/STANDBY switch to STANDBY and remove the amplifier from the
oscilloscope.
2. Remove the left side cover from the amplifier
3. Remove and rotate Jumper J611 (see Figure 3-9) 90 degrees to the horizontal position and reinsert
J611 connecting the two horizontal pins together.
4. Reinstall the amplifier in the oscilloscope.
5. While
de~ressing
the Channel 2 button, set the oscilloscope ON/STANDBY switch to ON. Continue
to hold the Channel 2 button for approximately 5 seconds.
After the amplifier is repaired, be sure to rotate J611 back to the vertical position. New calibration
constants are installed by performing calibration (pressing EA).
* The 11A52 is a noteable exception to this procedure as its calibration constants for the transient
response are stored in memory for each setting of the M377 amplifier's six V/div settings per channel.
Unless the values for these 12 calibration constants are manually recorded and re-entered after entering the
default values (by pressing and holding CH2 INPUT at turn-on), they must later be reset by observing the
transient response with a fast pulser. This is rarely worth the effort.
The l 1A52 calconstants for high frequency adjustments are as follows:
S3: CHI HFadj at ImV/div
S4: CHI HFadj at 2mV/div
SS: CHI HFadj at Sm V /div
S6: CHI HFadj at lOm V /div
S7: CHI HFadj at20mV/div
S8: CHI HFadj at SOmV/div
I8I: CH2 HFadj at ImV/div
I82: CH2 HFadj at 2mV/div
I 83: CH2 HF adj at Sm V /div
I84: CH2 HFadj at lOmV/div
I8S: CH2 HFadj at 20mV/div
I86: CH2 HFadj at SOmV/div