SERVO SYSTEM ADJUSTMENTS AND CHECKS
VE LOCITY GAIN CHECK
TROUBLE ANALYSIS AIDS 3C
GENERAL
Various types of malfunction can occur dur-ing the course of drive operation. No at-tempt has been made to correlate the many possible malfunctions to their most likely cause. However, as a troubleshooting aid on the broad subject of accessing errors, these four categories are definable:
• Seek errors
•
Address errors• On cylinder errors
• Seek monitor checks
Prior to beginning detailed tests or adjust-ments, perform the procedures in Drive Tests and Adjustments. If these tests and adjust-ments do not correct the malfunction or re-veal a correctable problem, proceed with the Power System Checks.
POWER SYSTEM CHECKS
OUTPUT VO L TAGES CHECK
Perform the following check with the drive performing continous 128-track seeks. The +SV and -SV adjustment procedures are locat-ed in the Drive Tests and Adjustments para-graphs of this section. All measurements should be made by connecting a digital volt/
ohmmeter at the logic chassis connection or at the capacitor in the case of -42V. The following voltages shall be present:
1. Ground to +20 (+20±2 vdc).
2. Ground to +S (+S.l±O.OS vdc).
3. Ground to +42 (+42±2 vdc).
4. Ground to -20 (-20±2 vdc).
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S. Ground to -42 (-42±2 vdc).
6. Ground to -S (-S.l±O.OS vdc).
EMERGENCY RETRACT TEST 1. Raise case assembly.
2. Press drive START switch to start drive motor and load heads.
3. Apply a ground to A13-14B and observe that heads unload.
4. Sync an oscilloscope negative on A13-l4B and observe the output at the -LQV card, location A12, TPF. The output at TPF should peak at 2.0 (±O.
5) volts during the retract.
S. Prepare drive for on line operation.
SERVO SYSTEM ADJUSTMENTS AND CHECKS
GE NERAL
The following procedures check the logic as-sociated with the servo. These procedures are applicable only if adjustments could not be made or if troubleshooting a malfunction-ing drive.
All servo system checks are written as inde-pendent procedures. If more than one check is being made, drive preparation steps may be omitted for subsequent checks.
VE LOCITY GAIN CHECK
Refer to the Velocity Gain Adjustment pro-cedure in the Drive Tests and Adjustments section for instructions on checking veloc-ity gain.
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FINE POSITION AMPLITUDE CHECK
1. Prepare drive for use with test soft-ware or field test exerciser.
2. Trigger oscilloscope negative external on wirewrap pin A04-07A (Not Forward) . 3. Connect oscilloscope channell to test
point F on card All (Fine Position Analog) .
4. Set oscilloscope volts per division control to 2 volts per cm and time per division control to 1 ms per cm.
5. Command continuous seeks between cylin-ders 000 and 001.
6. Amplitude of waveform (refer to figure 3-4) should be between 8.6 and 12.6 volts peak to peak. If voltage exceeds tolerance, replace card at All. If tolerance is still not met, replace card at AIO.
7. Prepare drive for on line operation.
ON CYLINDER DELAY CHECK
1. Prepare drive for use with test soft-ware or field test exerciser.
2. Trigger oscilloscope positive external at wirewrap pin A04-15A (On Cylinder Sense) .
OSCILLOSCOPE SETTINGS LOGIC GND TO SCOPE GND
VOLTS/DIY CH I - 2V/CM CH 2 - NOT USED
3. Connect oscilloscope channell to wire-wrap pin A04-03A (On Cylinder) .
4. Command continuous seeks between cylin-ders 000 and 001.
5. Observe that On Cylinder pulse occurs between 1.40 and 2.10 ms from start of the trace. If not, replace card A04.
6. Prepare drive for on line operation.
COARSE VELOCITY INTEGRATOR CHECK
This procedure checks operation of Desired Velocity Function Generator. Function Gener-ator smooths steps in coarse position error signal which are present during last 256 cylinders of a seek.
1. Prepare drive for use with test soft-ware or field test exerciser.
NOTE
Insert spare wirewrap pin (or equivalent) into back of con-nector attached to backpanel so oscilloscope probe can be attached.
2. Trigger oscilloscope positive external at wirewrap pin A09-26B (T~7).
3. connect oscilloscope channell to test point D on card A12.
TIME / DIY
IO.6(±2)V
p_p ~~HHHHHHYH~~~~a+++++++++~~~~~HHHH~~OV A-IMS/CM
B - NOT USED TRIGGERING
A- EXT NEG, A04-07A B- NOT USED
PROBE CONNECTIONS CH I TO AII-TPF CH 2 NOT USED
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9D48
Figure 3- 8. Fine Position Amplitude Waveform
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I .",
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,---4. Command continuous seeks between cylin-ders 000 and 256.
5. Adjust oscilloscope controls to display two sloped curves (refer to figure 3-9).
6. The amplitude of the last discontinuity (see figure 3-9) should be from .03 to .05 volts (ignore spike). If i t does not meet these specifications perform Digital to Analog Converter and Velocity Transducer Gain Uniformity Checks.
7. Prepare drive for on line operation.
DIGITAL TO ANALOG CONVERTER CHECK
The position converter output should be clamped at "negative saturation until tracks to go is less than 256 (T<256). During re-mainder of seek position converter output is under control of digital to analog con-verter.
1. Prepare drive for use with test soft-ware or with field test exerciser.
2. Trigger oscilloscope negative external at wirewrap pin A04-0BA (Not Rev Seek).
3. Connect oscilloscope channell to test point C on Card A12 (D/A Converter) . 4. Command continuous seeks between
cylin-ders 000 and 260.
ascI LLascaPE SETTINGS
LOGIC GND TO SCOPE GND VOLTS/DIY
CH I -.2V/CM CH 2 -NOT USED TIME / DIY
A-.5 MS/CM B - NOT USED TRIGGERING
A-EXT POS, A09 - 268 B- NOT USED
PROBE CONNECTIONS CH I TO AI2-TPD CH 2 NOT USED
5. Observe waveforms and evaluate them as follows (oscilloscope settings and wave-forms are shown on figure 3-l0):
a. Ensure that top waveform on figure
3~10has an amplitude of -10.5 volts maximum.
b. Ensure that steps on the bottom wave-form (except for the last two) have height between 20 and 60 mV. Last two steps should each have height of 40 mV.
6. If requirements of step 5 are not met, replace cards in A12 or A13.
7. Prepare drive for on line operation.
VELOCITY TRANSDUCER GAIN UNIFORMITY CHECK 1. Prepare drive for use with test
soft-ware or field test exerciser.
2. Trigger oscilloscope positive external at wirewrap pin A09-26B (T~7).
3. Connect oscilloscope channell to test point B on card A12 (velocity integrator output) .
4. Command continuous seeks between cylin-ders 000 and 007.
LAST DISCONTINU ITY (IGNORE THE SPIKE)
CH I
CH2
9049
Figure 3-9. Coarse Velocity Integrator Waveform
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OSCILLOSCOPE SETTINGS
LOGIC GND TO SCOPE GND VOLTS/DIV
CH I - 2V CH 2 - NOT USED TIME / DIV
A- 5MS B - NOT USED TRIGGERING
A-EXT NEG, A04-08A B- NOT USED
PROBE CONNECTIONS CH I TO AI2-TPC CH 2 NOT USED
-0- -- --- - --1
10.5V MAX
~~--J
OSCILLOSCOPE SETTINGS
LOGIC GND TO SCOPE GND VOLTS IDIV
CH I - 0.05V CH 2 - NOT USED TIME / DIV
A- 5 MS B - NOT USED TRIGGERING
A- EXT NEG, A04 -08A B- NOT USED
PROBE CONNECTIONS CH I TO AI2-TPC CH 2 NOT USED
- -r- -r- -... - r -r- -I-- -r- -r- - r -GROUND ~ - - - - - - - ----"if
REFERENCE 40 MV
~~~--~~--~-+--+--+--+-~-t
40 MV
~
I
. .
t- -I- -t- -r- -t- -+- -r -t- -r -t-
-NOTE
CD
LOWER WAVEFORM IS EXPANDEDVIEW OF THIS SECTION. 9050
Figure 3-10. Digital to Analog Converter Output Waveform
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5. Decaliprate horizontal sweep and adjust triggering control to observe both positive and negative ramps (see figure 3-11). Ramps represent integrated velocity sawtooth during last sev~~
cylinders of seek. Positive ramps are forward seek, negative ramps are re-verse seek.
6. Check voltages of second to last posi-tive and negaposi-tive ramps (refer to figure 3-11). Amplitude of each ramp should be 2.2 to 2.8 volts and difference in amplitudes between two ramps should be less than 0.4 volts. If these require-ments are not met, either card A12 or velocity transducer is defective.
7. Prepare drive for on line operation.
FINE ENABLE SWITCHING LEVEL CHECK
This procedure verifies that Fine Enable switches in at proper level. This signal, along with T~l, set Fine FF.
1. Prepare drive for use with test soft-ware or field test exerciser.
2. Trigger oscilloscope negative external at wirewrap pin A04-07A (Not Forward Seek) .
3. Connect oscilloscope channel 2 to test point B on card A12 (velocity integra-tor output).
4. Connect oscilloscope channell to wire-wrap pin A04-l6B (FINE).
CSCI LLCSCCPE SETTINGS LOGIC GND TO SCOPE GND
VOLTS/DIV CH I - IV/CM CH 2 - NOT USED TIME / DIV
A- .5 MS/CM B - NOT USED TRIGGERING
A- EXT POS, A09-26B B- NOT USED
PROBE CONNECTIONS CH I TO A12- TPB
5. Set oscilloscope trigger mode to chop.
6. Command continuous seeks between cylin-ders 000 and 001.
7. Check that Fine signal switches to a logical 1 when positive or negative velocity signal is between 1.3 and 1.5 vol ts (refer to figure 3-12). If 'these requirements are not met replace card in All.
8. prepare drive for on line operation.
TRACK SERVO AMPLITUDE CHECK
This test checks the amplitude of track servo signal output of servo preamp.
1. Prepare drive for use with test soft-ware or field test exerciser.
2. Trigger oscilloscope internal positive.
NOTE
Insert spare wirewrap pin (or equivalent) into back of con-nector attached to backpanel so oscilloscope can be attached.
3. Connect oscilloscope channell to wire-wrap pin AlO-25B (dibit signals from servo preamp) .
4. Connect oscilloscope channel 2 to wire-wrap pin AlO-23B (dibit signals from servo preamp).
SECOND LAST RAMP
_~ ______ 1~~_~~M~ _______ _
CH 2 NOT USED 9051
Figure 3-11. Integrated Velocity Waveform
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OSCILLOSCOPE SETTINGS
PROBE CONNECTIONS CH I TO A04-168
Figure 3-l2. Fine Enable switching Waveform
5. Set oscilloscope trigger mode to add
OSCILLOSCOPE SETTINGS
9. If one side of servo head is shorted to ground, a waveform similar to that shown in figure 3-14 will be displayed. The servo will continue to function, but intermittent seek errors occur.
10. If track servo amplitude is not as PROBE CONNECTIONS
CH I TO AIO-258
(
\ '-.
OSCILLOSCOPE SETTINGS LOGIC GND TO SCOPE GND
VOLTS IDIV CH 1- .lV/CM CH2-.IV/CM TIME I DIY
A- .5fLS/CM B - NOT USED TRIGGERING
A- INT NEG B- NOT USED PROBE CONNECTIONS
CH I TO AIO-258
CH 2 TO AIO- 238 9054
Figure 3-14. Shorted Servo Head Waveform
CYLINDER PULSE SWITCHING LEVEL CHECK 9. Connect oscilloscope channel- 1 to wire-NOTE
If requirements of steps 1 through 7 are met i t is not necessary to perform remainder of this procedure.
1. Prepare drive for use with test soft-ware or field test exerciser.
2. Trigger oscilloscope positive internal.
3. Connect oscilloscope channell to wire-wrap pin A04-22A (Cy~inder Pulses).
4. Command continuous seeks between cylinders 000 and 004.
5. Check for series of positive-going 10 (±2.5) ~sec cylinder pulses.
6. Trigger oscilloscope external positive at A04-03A (On Cylinder).
7. Check that last cylinder pulse (gener-ated from leading edge of On Cylinder) is present and has pulses width of approximately 0.2 ~sec.
8. Trigger oscilloscope negative external at wirewrap pin A04-28B (Cylinder Detect A) •
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wrap pin AIO-09B (Track Servo Signal) . IV. Command continuous seeks between
cylin-ders 000 and 004.
11. Set oscilloscope time per division to 50 ~sec per cm and volts per division to 0.2V per cm.
12. Check that Track Servo signal is be-tween -0.3 and -0.5 volts at beginning of sweep.
13. Trigger oscilloscope positive external at A04-28B (Cylinder Detect A) and check that track servo signal is be-tween -0.1 and +0.1 at beginning of the sweep.
14. Trigger oscilloscope negative external at wirewrap pin A04-27B (Cylinder Detect B). Check that Track Servo signal is between +0.3 and +0.5 volts at beginning of sweep.
15. Trigger positive external and check that Track Servo signal is between -0.1 and +0.1 at beginning of sweep.
16. If levels are not met replace card AIO.
17. Prepare drive for on line operation.
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