Tektronix 620-0295-00 User manual

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I Tektronix, Inc.
P.O. Box 500
Beaverton, Oregon 97077
MANUAL PART NO.
070-3732-00
COMMITTED TO EXCELLENCE
620-0295-00
LOW VOLTAGE
POWER SUPPLY
SERVICE MANUAL
First Printing FEB 1981 ·

WARNING I
THE FOLLOWING SERVICING INSTRUCTIONS ARE
FOR USE BY QUALIFIED PERSONNEL ONLY. TO
AVOID PERSONAL INJURY, DO NOT PERFORM ANY
SERVICING OTHER THAN THAT CONTAINED IN
OPERATING INSTRUCTIONS UNLESS YOU ARE
QUALIFIED TO DO SO.
Copyright
©
1981 by Tektronix, Inc., Beaverton, Oregon.
Printed in the United States of America. All rights reserved.
Contents of this publication may not be reproduced in any
form without permission of Tektronix, Inc.
This instrument, in whole or in part, may be protected by one
or more U.S. or foreign patents or patent applications.
Information provided on request by Tektronix, Inc., P.O. Box
500, Beaverton, Oregon 97077.
TEKTRONIX is a registered trademark of Tektronix, Inc.

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MANUAL REVISION STATUS
PRODUCT: 620-0295-00 Low Voltage Power Supply
This manual supports the following versions of this product: Part Numbers 620-0295-00 and up
REV. DATE DESCRIPTION
@ FEB 1981 Original Issue
620-0295-00 POWER SUPPLY @

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Section 1
Section 2
Section 3
Section 4
620-0295-00 POWER SUPPLY
CONTENTS
INTRODUCTION Page
About This Manual ..................................... 1-1
Description of the Module ............................... 1-1
General ............................................. 1-1
Physical Description ................................. 1-1
SPECIFICATIONS
Physical ............................................... 2-1
Electrical .............................................. 2-1
Environmental .......................................... 2-3
External Connections ................................... 2-4
MAINTENANCE
Safety Summary........................................ 3-1
General ................................................ 3-1
Changing the Line Voltage .............................. 3-2
Troubleshooting ........................................ 3-2
Equipment Required ................................. 3-3
Preparation .......................................... 3-4
Control Circuit ....................................... 3-4
Primary Circuit ...................................... 3-6
Logical On/Off Switch ................................ 3-7
DCSupplies ......................................... 3-8
Timing Circuit ....................................... 3-8
Assembly/Disassembly ................................. 3-9
Replacing the Line Rectifier .......................... 3-9
Replacing the Switching Transistors .................. 3-9
Removing the Inverter Board ......................... 3-1O
Removing the Regulator Board........................ 3-11
Replacing the+ 5 V Rectifier ......................... 3-12
Access to the Cavity ................................. 3-1 2
PERFORMANCE CHECK
Equipment Required ................................. 4-1
Procedures ............................................ 4-2
NOTE
Refer to the host product service manual for the
adjustment procedure.
DCVoltages ......................................... 4-2
INIT-0 and PWRFL-0................................. 4-2
Maximum and Minimum Line Voltage.................. 4-3
Current Limiting and Maximum Loads ................. 4-3
@ ii

iii
Section 5
Section 6
Section 7
Section 8
Appendix A
Table
THEORY OF OPERATION
Introduction ............................................ 5-1
DC Supplies ......................................... 5-2
System Interface Signals ............................. 5-2
Block Description ...................................... 5-3
Detailed Circuit Description ............................. 5-4
Primary Circuit ...................................... 5-4
Control Circuit ....................................... 5-6
DC Supplies ......................................... 5-8
Timing Circuit ....................................... 5-11
REPLACEABLE ELECTRICAL PARTS
DIAGRAMS AND SCHEMATICS
REPLACEABLE MECHANICAL PARTS
SIGNAL DEFINITIONS AND REFERENCES
TABLES
Description Page
2-1 Line Input................................................. 2-1
2-2 DC Supplies .............................................. 2-2
2-3 TTL Signals ............................................... 2-3
2-4 Environmental Limits ...................................... 2-3
2-5 External Connections ..................................... 2-4
4-1 Power Supply Voltage Limits ............................... 4-2
5-1 Base Drive Circuit States .................................. 5-8
@
620-0295-00 POWER SUPPLY

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Figure
1-1
1-2
2-1
3-1
3-2
3-3
3-4
3-5
3-6
3-7
3-8
3-9
3-10
3-11
3-12
3-13
4-1
4-2
4-3
5-1
5-2
5-3
5-4
5-5
5-6
5-7
620-0295-00 POWER SUPPLY
ILLUSTRATIONS
Description Page
The 620-0295-00 Low Voltage Power Supply ............... vi
Line Voltage Switches ..................................... 1-1
Dimensions ............................................... 2-1
Changing Line Voltage .................................... 3-2
Test Connectors .......................................... 3-3
Connection of Test Load................................... 3-4
Base Drive Test Point ..................................... 3-5
Base Drive Waveform ...................................... 3-5
Inverter Dead Time ........................................ 3-5
Connecting the Current Probe ............................. 3-6
Bypassing Triac ........................................... 3-6
Inverter Waveform ......................................... 3-7
Mounting of Switching Transistors ......................... 3-9
Removing the Inverter Board ............................... 3-1O
Removing the Regulator Board ............................. 3-11
Mounting the Diodes to the Heat Sink ...................... 3-12
Power Supply Test Points.................................. 4-2
Power-Up Waveform ...................................... 4-3
Power-Down Waveform .................................... 4-3
Simplified Inverter Circuit. ................................. 5-1
Configuration for the 115 V Line ........................... 5-4
Configuration for the 230 V Line ........................... 5-5
Logical On/Off Switch ..................................... 5-6
Pulse Width Modulator 1.C.................................. 5-7
Typical Post-Regulator Circuit ............................. 5-9
Foldback Current Limiting Characteristic ................... 5-9
@ iv

DO NOT SERVICE ALONE
SAFETY SUMMARY
POWER SOURCE
Do not perform service or adjustment of this module
unless another person capable of rendering first aid
and resuscitation is present.
USE CARE WHEN SERVICING WITH
POWER ON
Dangerous voltages exist at several points in this
module. To avoid personal injury do not touch exposed
connections or components while the power is on.
Disconnect the power before removing protective pan-
els, soldering, or replacing components.
After the power has been disconnected, the neon
flasher on the Inverter board indicates that dangerous
voltages still are present in the filter capacitors.
620-0295-00 POWERSUPPLY @
This module is intended to operate from a power
source that applies less than 250 volts rms between
the supply conductors or between either the supply
conductor and ground. A protectjve ground connection
by way of the grounding conductor in the power cord is
essential for safe operation.
V

Figure 1-1. The 620-0295-00 Low Voltage Power Supply.
vi
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620-0295-00 POWER SUPPLY

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Section 1
INTRODUCTION
ABOUT THIS MANUAL
This manual provides the technician with service
information for the 620-0295-00 Low Voltage Power
Supply module (Figure 1-1). It includes specifications,
troubleshooting information, performance check pro-
cedures, circuit descriptions, and schematics.
The adjustment procedure is described in the service
manual for the product in which the power supply is
installed.
GENERAL
DESCRIPTION OF THE MODULE
Controls and Indicators
The module is a high-efficiency power supply intended
for installation in a number of Tektronix products. The
product in which it is installed is referred to as the host
product in this manual.
The module occupies approximately 5 by 5 by 9.5
inches within the chassis of the host product. An
external heat sink is approximately 7.5 by 1
O
inches.
Screws through the heat sink attach the module to the
chassis.
PHYSICAL DESCRIPTION
Main Assemblies
The power supply circuits are contained primarily on
four boards:
• A VDE Line Filter board to supplement the chassis-
mounted line filter.
• A Line Voltage Selector board.
• An Inverter board, which rectifies and filters the line
voltage, then chops it at 20 kHz to drive the inverter
transformer. The Control circuit regulates voltages
by varying the width of the 20 kHz pulses according
to the input and output voltages and load current.
• A Regulator board, which rectifies and filters output
of the inverter transformer and provides post-
regulation. It also contains protection circuits and
asserts TTL signals for use by the host product.
AC is available to drive fans and other components.
620-0295-00 POWERSUPPLY
• Two Line Voltage switches allow operation on either
115 or 230 VAC nominal line voltage. These switch-
es are accessible through the heat sink (Figure 1-2).
• A Logical On/Off switch isolates the system switch
from line voltage. The host product turns on the
power supply by grounding the switch s·ignal line
(OFF-1
/ON-0).
This allows the host product to keep
the power on until its operations are complete even
if the operator has turned off the system power
switch.
• A high voltage warning flasher indicates the
presence of dangerou·s voltages on the Inverter
board.
FUSE
LINE
VQLTAGE
SWITCHES
3732•34
Figure 1-2. Line Voltage Switches.
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1-1

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Section 2
SPECIFICATIONS
PHYSICAL
Figure 2-1 gives the dimensions of the module. It
weighs 9.5 lbs (4.3 kg).
ELECTRICAL
Tables 2-1, 2-2, and 2-3 give the electrical specifica-
tions for the Power Supply module. The following
definitions explain the column headings.
Characteristic: Property of equipment.
Performance Requirement: A statement that defines a
characteristic in quantitative terms of performance,
usually in limit form. The Performance Check section of
this manual describes procedures to verify the perfor-
mance.
Characteristic
Line voltage
115 V nominal
230 V nominal
Frequency
Crest factor
Fuses
Maximum power
consumption
Table 2-1
LINE INPUT
Performance
Requirement
90 to 132 V
180 to 264 V
Supplemental
Information
48 to 6!3Hz
1.35 to 1.414
115 V: 6.25 A
medium
230 V: 3 A fast
35owa
aExcludlng AC for fans and disk. If maximum current were drawn from all DC
supplies simultaneously, it would result in Input power of approximately
510W.
620-0295-00 POWER SUPPLY
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Supplemental Information: Statements that explain
performance requirements or that provide reference
information. These are not supported by performance
check procedures in the manual.
The performance requirements .cited in this section are
valid only within the following conditions:
• The load on the
+
5 V supply is between 3 and 30 A.
• AC line supply is 48 to 66 Hz,90 to 132 V or 180 to
264 V,with the crest factor between 1.35 and 1.414.
The crest factor is the ratio of peak to rms voltage. It
falls below 1.414 as the voltage departs from a sine
wave.
• The module has been calibrated within and is
operating within the specified environmental limits.
Figure 2-1. Dimensions.
2-1

SPECIFICATIONS
Table 2-2
DC SUPPLIES
Characteristic
+ 5 V Supply a
Regulation
Ripple
Minimum load
Maximum load
Foldback cur-
rent limiting
Overvoltage
protection
+ 12 V Supply
Regulation
Ripple
Maximum load
Foldback cur-
rent limiting
Reverse volt-
age clamp
Overvoltage
protection
+ 24 V Supply
Regulation
Ripple
Maximum load
Foldback cur-
rent limiting
Reverse volt-
age clamp
Performance
Requirement
±3%
30A
<37 A
±3%
4A
<6A
±3%
1.8 A
<2.8A
aS.075 Vat point of regulation In host product.
Supplemental
Information
Measured at sense
line
100 mV p-p
3Ab
:,;;;;1v
C
20 mV p-p
-0.7V
±15 voe
±17 V peak
20 mV p-p
-0.7V
bMinimumloads are not required for the other supply voltages.
0speclal Requirements for Memory Boards: During power up, the -12 V
supply must reach -5 Volts before the +12 V supply reaches +1 Ov.During
power down, the +1 2 V supply must not overshoot.
2-2
------ -- --- ------------
Characteristic
+ 55 V Supply
Regulation
Temperature
coefficient
Ripple
Maximum load
Foldback cur-
rent limiting
Reverse volt-
age clamp
-5.2 V Supply
Regulation
Ripple
Maximum load
Foldback cur-
rent limiting
Reverse volt-
age clamp
-12 V Supply
Regulation
Ripple
Maximum load
Foldback cur-
rent limiting
Reverse volt-
age clamp
@
Performance
Requirement
±2%
1.25 A
<1.6A
±4%
4A
<4.8A
±3%
1 A
<1.5A
Supplemental
Information
Initial setting:
+55.1 V±100mV
5 mV per °C average
from Oto 10°c at
VR579
25 mV p-p at 60 Hz
50 mV p-p at 40 kHz
-0.7V
100 mV p-p
+0.7 V
20 mV p-p
+0.7V
620-0295-00 POWERSUPPLY

Characteristic
INIT-0
PWRFL-0
Table 2-3
TTL SIGNALS
Performance
Requirement
Must stay low at least
50 ms after
+
5 V
supply comes into re-
gulation. Goes low
when
+
5 V supply
drops out of regula-
tion.
Must go low at least
11 ms before INIT-0.
ENVIRONMENTAL
Supplemental
Information
TTL initialization
signal
TTL power failure
warning signal
Table 2-4 describes the environment in which the
Power Supply module is intended to operate. The
performance requirements in the electrical specifica-
tion are valid only
if
these environmental limits are met.
620-0295-00 POWERSUPPLY
@
SPECIFICATIONS
Table 2-4
ENVIRONMENTAL LIMITS
Characteristic Information
Temperature
Operating Heat sink:
o
to 40°C
ambient Circuit boards: Oto 70°C
Non-operating -55 to 75°C
Humidity
Operating and Up to 90% noncondensing
Non-operating
Altitude
Operating 15,000 ft (4.5 km). Decrease maximum
operating temperature -1 °C for every
1,000 ft (300 m) above 5,000 ft (1.5 km).
Non-operating 50,000 ft (15 km)
Vibration
Non-operating Withstands 0.Q15 in p-p (0.38 mm), iO
to 55 Hz sine wave, 15 min each axis
and 10 min each axis at resonance or
55 Hz.
Shock
Non-operating Withstands 3 g, halfsine, 11 ms, 18
shocks
Bench handling
Non-operating Withstands drop from 45 degrees, 4 in
(102 mm); or equilibrium on all signifi-
cant faces.
Packaged product Qualifies under National Safe Transit
vibration and shock Association Pre-Shipment Test Proce-
dure, Project 1A-B-1, when packaged as
shipped from factory.
Electromagnetic Qualifies under FCC standard for Class
compatibility A computing devices (Docket No.
20780) with respect to conducted
emissions.
For radiated emissions, refer to specifi-
cation for the host product.
Line transients
Oscillatory surge Withstands oscillatory surges up to 2.5
kV at i .5 MHz.
Ride-through At line voltages between 95 and 132 V
or 180 and 264 V, supplies remain
within regulation for at least 20 ms after
loss of line voltage. For line voltages
be~ween90 and 95 V, supplies remain
in regulation for at least 10 ms.
2-3

SPECIFICATIONS
EXTERNAL CONNECTIONS
Table 2-5 describes the connections between the
Power Supply module and the host product.
2-4
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Connector
J71
J72
J73-1
-2
-3
-4
-5
-6
-7
-8
-9
-10
J74-1
-2
-3
-4
J76-1
-2
J1001 1-3
-2
J1002 1-3
-2
J1003
J1004
J9001
Table 2-5
EXTERNAL CONNECTIONS
Name Use
+5 RTN Return for+ 5 V supply
+5 + 5 Voutput
+12V + 12 Voutput
+ 12 V + 12 V output
G SENSE Ground sense from host
product
+5 V SENSE + 5 V sense from host
product
PWRFL-0 Power failure warning
INIT-0 Power up initialization
signal
GND Return for all supplies
except+ 5 V
-12V -12 V output
-5.2V -5.2 V output
-5.2V -5.2 V output
GND Ground
+24V + 24 V output
+24V + 24 V output
+55V + 55 V output
OFF-1/ON-0 Power control line from host
product
GND Ground
115 VAC output
Safety ground
115 VAC output
(empty)
115 VAC output
115 VAC output
Power cord
620-0295-00 POWERSUPPLY

Section 3
MAINTENANCE
SAFETY SUMMARY
WARNING
I
The VOELine Filter, Line Voltage Selector, and
Inverter boards are connected directly to the AC
lines. Toavoid injury by electrical shock an
isolation transformer should be used during ser-
vicing of these boards.
Turning off the host product does not disconnect
the Power Supply module from the AC lines nor
does it always shut down the DC supplies on
certain host products. Do not rely on the host
system switch to remove voltages. Disconnect
the power cable from the AC line.
After the power has been disconnected, the neon
flasher on the Inverter board indicates that dan-
gerous voltages are still present in the filter
capacitors.
Some fault conditions may cause the switching
transistors or other primary components to ex-
plode. Toavoid injury to your eyes wear safety
glasses while servicing the power supply.
GENERAL
• Assembly/disassembly of the module.
The module does not require routine maintenance.
This section contains procedures and information on
the following topics: Refer to the Performance Check section for the
performance check procedure. Refer to the host
product service manual for the adjustment procedure.
• Changing the line voltage.
• Troubleshooting and bringing up supplies which
have been repaired.
620-0295-00 POWERSUPPLY @
3-1

MAINTENANCE
PREPARATION
1. Verify that the Line Voltage switches are set to the
proper voltage.
I
WARNING
I
The fuse holder is connected directly to the AC
lines without an intervening switch. Toavoid
injury by electrical shock, disconnect the power
cord before removing the fuse.
2. Verify that the proper fuse is installed. Refer to
Table 2-1 for the fuse specification.
3. Connect a suitable load, such as the one described
in Figure 3-3.
Figure 3-3. Connection of Test Load.
3-4
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CONTROL CIRCUIT
This test examines the output of the Control circuit
before connecting the Power Supply to the AC line.
An
external source provides local DC to operate the
circuit. The Logical On/Off switch is tested separately.
1. Set the oscilloscope as follows:
CH 1 VOLTS/DIV
TIME/DIV
TRIGGER SOURCE
TRIGGER SLOPE
TRIGGER MODE
10
10µ,s
CHANNEL1
+
AUTO
2. Connect Channel 1 of the oscilloscope to Pin 1 of
the base drive transformer (T540, Figure 3-4).
Position the ground reference in the center of the
screen.
3. Connect the external DC source to J63 using the
harmonica connector shown in Figure 3-2A. If the
external supply does not include a voltmeter,
connect one across its output. (The loop between
Pins 1 and 2 of the harmonica connecter disables
the+ 5 V current limiting circuit. The current sense
amplifier does not operate properly in the absence
of line voltage.)
4. Turn on the external DC source. Gradually bring up
the DC voltage while observing the oscilloscope
display. The Schmitt trigger should turn on when
the voltage reaches about 21 V. At this point, the
display should appear similar to that shown in
Figure 3-5.
Failure to trigger may be caused by bad transistors
in the Schmitt trigger. Departure from the waveform
shown in the figure indicates a fault in the Pulse
Width Modulator circuit or the Base Drive circuit.
NOTE
If the switching transistors have failed, CR45
7
and CR555 may have become leaky and should
also be replaced.
620-0295-00 POWER SUPPLY

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5. Gradually turn down the DCvoltage. The Schmitt
trigger should turn off at about 11 V.
6. Reset the external DCto 24 V.
7. Change the oscilloscope setting as follows:
B TIME/DIV 1
µ,s
HORIZ DISPLAY A INTEN
B SOURCE STARTS AFTER
DELAY
8. Adjust DELAYTIME POS until the intensified zone
agrees with that shown in the top of Figure 3-6.
Figure 3-4. Base Drive Test Point.
620-0295-00 POWERSUPPLY
@
MAINTENANCE
9. Change HORIZ DISPLAY to B DLY'D and verify that
the dead time interval (shown in Figure 3-6) is
equal to or greater than 4.3
µ,s.
If it is not, replace
U575.
10. Reset HORIZ DISPLAY to A.
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3732-8
Figure 3-5. Base Drive Waveform.
11
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3732-9
Figure 3-6. Inverter Dead Time.
3-5

MAINTENANCE
PRIMARY CIRCUIT
This test applies AC to the Primary circuit. The test
checks the primary side of the inverter and the local
DCsupply for the Control circuit.
1. Set up the oscilloscope and external supply as
described in Steps 1, 2, 3, and 6 of the preceding
test.
2. Turn off the external DCsupply.
3. Connect the DC current probe amplifier output to
Channel 2.
3-6
a. Connect the current probe to Lead 9 of the
inverter transformer (T320). This is the white
wire located as shown in Figure 3-7.
b. Set AMPS/DIV on the current probe amplifier
to 2 A.
c. Set Channel 2 VOLTS/DIV to the value
specified on the amplifier (typically 10 mV).
d. Position the ground reference two divisions
from the bottom of the screen.
Figure 3- 7. Connecting the Current Probe.
@
4. Place the jumper (Figure 3-2C) on J60 (Figure 3-8).
,::~isbypasses the triac. It also bypasses the
Logical On/Off Switch and the power switch on the
host product.
5. Verify that the autotransformer is off and that the
voltage control is set to 0. Connect the power
supply to the isolation transformer, and then
connect the isolation transformer to the autotrans-
former.
6. Turn on the external DCsupply.
~
The +5 Vcurrent limiting circuit is disabled
during this portion of the test. Toavoid damage to
the supply, carefully observe the oscilloscope
display for current greater than 4 A (2 divisions).
3732-11
Figure 3~8. Bypassing Triac.
620-0295-00 POWERSUPPLY