Supplement
THS720A MOD NV TekScopet
Component-Level Information Package
070-9750-02
Supplement
THS720A MOD NV TekScopet
Component-Level Information Package
070-9750-02
This document applies to to serial number
B030100 and above and firmware version 1.00
and above.
First printing: July 1998
Warning
The servicing instructions are for use by qualified
personnel only. To avoid personal injury, do not
perform any servicing unless you are qualified to
do so. Refer to all safety summaries prior to
performing service.
Copyright E T ektronix, Inc. All rights reserved.
T ektronix products are covered by U.S. and foreign patents, issued and pending. Information in this publication supercedes
that in all previously published material. Specifications and price change privileges reserved.
Printed in the U.S.A.
T ektronix, Inc., P.O. Box 1000, Wilsonville, OR 97070–1000
TEKTRONIX and TEK are registered trademarks of T ektronix, Inc.
T ek Secure is a registered trademark of Tektronix, Inc.
T ekTools, TekScope, and IsolatedChannel are trademarks of Tektronix, Inc.
Pursuant to DFARS 252.227-7013(e), T ektronix Inc. hereby grants to the Government a nonexclusive, paid-up license
throughout the world of the scope set forth therein for Government purposes for any commercial manuals provided by
T ektronix Inc. under this contract.
WARRANTY
T ektronix warrants that this product will be free from defects in materials and workmanship for a period of three (3) years
from the date of purchase from an authorized T ektronix distributor. If any such product proves defective during this
warranty period, T ektronix, at its option, either will repair the defective product without charge for parts and labor, or will
provide a replacement in exchange for the defective product. Batteries are excluded from this warranty.
In order to obtain service under this warranty, Customer must notify Tektronix of the defect before the expiration of the
warranty period and make suitable arrangements for the performance of service. Customer shall be responsible for
packaging and shipping the defective product to the service center designated by T ektronix, with shipping charges prepaid.
T ektronix shall pay for the return of the product to Customer if the shipment is to a location within the country in which the
T ektronix service center is located. Customer shall be responsible for paying all shipping charges, duties, taxes, and any
other charges for products returned to any other locations.
This warranty shall not apply to any defect, failure or damage caused by improper use or improper or inadequate
maintenance and care. T ektronix shall not be obligated to furnish service under this warranty a) to repair damage resulting
from attempts by personnel other than T ektronix representatives to install, repair or service the product; b) to repair
damage resulting from improper use or connection to incompatible equipment; or c) to service a product that has been
modified or integrated with other products when the effect of such modification or integration increases the time or
difficulty of servicing the product.
THIS WARRANTY IS GIVEN BY TEKTRONIX WITH RESPECT TO THIS PRODUCT IN LIEU OF ANY
OTHER WARRANTIES, EXPRESSED OR IMPLIED. TEKTRONIX AND ITS VENDORS DISCLAIM ANY
IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
TEKTRONIX’ RESPONSIBILITY TO REPAIR OR REPLACE DEFECTIVE PRODUCTS IS THE SOLE AND
EXCLUSIVE REMEDY PROVIDED TO THE CUST OMER FOR BREACH OF THIS WARRANTY. TEKTRONIX
AND ITS VENDORS WILL NOT BE LIABLE FOR ANY INDIRECT , SPECIAL, INCIDENTAL, OR
CONSEQUENTIAL DAMAGES IRRESPECTIVE OF WHETHER TEKTRONIX OR THE VENDOR HAS
ADVANCE NOTICE OF THE POSSIBILITY OF SUCH DAMAGES.
Service Assurance
If you have not already purchased Service Assurance for this product, you may do so at any time during the product’s
warranty period. Service Assurance provides Repair Protection and Calibration Services to meet your needs.
Repair Protection extends priority repair services beyond the product’s warranty period; you may purchase up to three
years of Repair Protection.
Calibration Services provide annual calibration of your product, standards compliance and required audit documentation,
recall assurance, and reminder notification of scheduled calibration. Coverage begins upon registration; you may purchase
up to five years of Calibration Services.
Service Assurance Advantages
H Priced well below the cost of a single repair or calibration
H Avoid delays for service by eliminating the need for separate purchase authorizations from your company
H Eliminates unexpected service expenses
For Information and Ordering
For more information or to order Service Assurance, contact your local T ektronix representative and provide the information below. Service Assurance may not be available in locations outside the United States of America.
Name VISA or Master Card number and expiration
Company date or purchase order number
Address Repair Protection (1,2, or 3 years)
City , State, Postal code Calibration Services (1,2,3,4, or 5 years)
Country Instrument model and serial number
Phone Instrument purchase date
T o learn the location of your nearest Tektronix representative, please call 1-800-TEK-WIDE in North America,
1-503-627-7111 elsewhere, or look us up on the World Wide Web at http://www.tek.com.
Introduction
This Component-Level Information Package (CLIP) provides component-level
theory of operation, an electrical parts list, and schematic diagrams for the
THS720A MOD NV.
This document is a supplement to the THS710A, THS720A, THS730A &
THS720P Service Manual, part number 070-9752-XX. The Service Manual
covers module-level information that also applies to the THS720A MOD NV.
The section below describes the differences between a standard THS720A and
the THS720A MOD NV. The sections that follow contain the electrical parts list
and schematic diagrams.
THS720A Mod NV Description
The THS720A MOD NV is identical to a standard THS720A except for the three
differences below:
H The THS720A MOD NV includes two P6101B passive probes with 1×
attenuation in addition to the two standard P6117 probes (10X attenuation).
H The THS720A MOD NV includes the THS710A, THS720A, THS730A &
THS720P Service Manual, which is part number 070-9752-XX.
H The THS720A MOD NV includes this document, the THS720A MOD NV
Component-Level Information Package, which is part number 070-9750-XX.
NOTE. For your convenience, you can insert this document into the back of the
binder for the THS710A, THS720A, THS730A & THS720P Service Manual.
THS720A MOD NV Component-Level Information Package
1
Introduction
Related Documents
This document must be used in combination with the THS710A, THS720A,
THS730A & THS720P Service Manual, part number 070-9752-XX. The Service
Manual contains information about specifications, general maintenance,
disassembly and troubleshooting.
CAUTION. To prevent product damage, refer to Chapter 6 Maintenence in the
THS710A, THS720A, THS730A & THS720P Service Manual for information
about ESD prevention.
For information about product operation and applications, refer to the THS710A,
THS720A, THS730A & THS720P User Manual, part number 070-9731-XX.
For information about operating the product over the RS-232 interface, refer to
the THS710A, THS720A, THS730A & THS720P Programmer Manual, part
number 070-9751-XX.
2
THS720A MOD NV Component-Level Information Package
Component-Level Theory of Operation
This section describes the electrical operation of the THS720A MOD NV. Refer
to the schematics in the Component-Level Diagrams section as necessary.
Logic Conventions
This manual refers to digital logic circuits with standard logic symbols and
terms. Unless otherwise stated, all logic functions are described using the
positive logic convention: the more positive of the two logic levels is the high
(1) state and the more negative level is the low (0) state. Signal states may also
be described as “true” meaning their active state or “false” meaning their
non-active state. The specific voltages that constitute a high or low state vary
among the electronic devices.
Active-low signals are indicated by an asterisk (*) following the signal name,
for example IRQ*. Signal names are considered to be either active-high,
active-low, or to have both active-high and active-low states.
Oscilloscope System
Acquisition System
Each of the two oscilloscope input signals enters the main board and passes
through an attenuator and preamplifier. Then each signal passes through an
isolation interface before reaching the trigger circuitry and sampler/digitizer. The
digitized signals are written into system memory for transfer to the display
system.
The acquisition system amplifies the input signals, samples them, converts them
to digital signals, and controls the acquisition process under direction of the
processor system. The acquisition system includes the trigger, acquisition timing,
and acquisition control circuitry.
Attenuators.
attenuation factor. The processor system controls the attenuators with a serial
interface as well as with DC control voltages.
The Main Board assembly contains two attenuator hybrids (AT1 and AT2). To
allow floating measurements, the attenuators are individually isolated from the
rest of the Main Board by an isolation interface. Power to the attenuators is
coupled through transformers. Opto-isolators couple control voltages and DC
control signals to each attenuator. Transformers couple the high-frequency signal
Circuitry in the attenuator selects the input coupling and
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THS720A MOD NV Component-Level Information Package
3
Component-Level Theory of Operation
path from each attenuator to the main board. Opto-isolators couple the low-frequency signal path from each attenuator to the main board.
Each attenuator hybrid contains two attenuators, an AC coupling capacitor, three
relays, three relay drivers, and a preamplifier. The AC/DC coupling relay couples
the output of the BNC to the other relays in the attenuator hybrid. For AC
signals, the AC/DC coupling relay inserts a coupling capacitor into the input
signal path. The second relay selects a X10 attenuation factor. The third relay
selects a X100 attenuation factor.
Sampler Driver.
The output of the attenuator drives the sampler driver (U44)
4
inputs. The sampler driver provides gain amplification, bandwidth limit filters,
and outputs for the sampler and trigger signal paths.
Daculator.
The daculator (U5) performs the function of sixteen independent
5
D/A converters. The daculator provides DC control voltages to the attenuator
hybrids and acquisition system. The CPU controls the daculator serially.
Sampler.
The sampler IC (U7) provides two complete acquisition channels. It
7
contains all of the functions associated with sampling, A/D conversion, trigger
placement, and time base control.
Using a 30.303 MHz clock, the Sampler samples the analog signals from the
Sampler driver at up to a 500 MS/s rate. It converts each sampled value into an
8-bit digital value. The A/D reference voltage is 2.5 V.
The sampler finds the approximate trigger position by counting clocks. At high
sample rates, it locates precise trigger position by acquiring the trigger signal and
interpolating it to find the zero crossing.
Acquisition Memory.
The acquisition memory consists of 128KB-by-8
7
SRAM (U9). The CPU reads this memory through the sampler.
Trigger.
The trigger IC (U47) provides all the functions of the trigger
6
system except video sync separation, which is provided by a separate sync
separator IC (U65).
The sampler driver selects the trigger source. The analog trigger signal is sent to
the trigger IC directly or through filters, which perform the high-frequency reject
or low-frequency reject functions.
Next, the signal is compared to two reference thresholds (i.e., trigger levels).
The difference between the thresholds set the amount of hysteresis; an increased
hysteresis setting performs the noise-reject function. The polarity of the
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THS720A MOD NV Component-Level Information Package
DMM System
Component-Level Theory of Operation
comparator can be switched to change the trigger slope. A shift register controls
filter selection, slope selection, and mode selection.
The trigger IC also contains digital logic and a timer to provide the pulse-width
trigger functions.
The output of the trigger integrated circuit is a sent to the sampler.
The video sync separator (U65) locates vertical sync pulses and detects even and
odd fields. Its output is sent to the trigger IC and to the sampler.
The DMM input enters the Main board and passes through a switching
network to select the meter function and range. The DMM signal is converted to
a digital value by the DMM IC (U36).
DC V olts. The DC Volts circuit uses voltage dividers to cover all ranges except
the most sensitive range (400 mVDC). For the 400 mVDC range, the input
signal is applied without attenuation to the DMM IC. Input latching relay (K1)
provides the switching between the 400 mV range and other ranges.
AC V olts. The signal applied to the input of the DMM IC is not AC coupled;
therefore, both AC and DC components are processed. The RMS converter (U8)
provides two outputs, the DC component of the signal and the RMS value of the
DC + AC components. Analog switch (U29) allows the DMM IC to select and
measure the composite RMS value and the DC component of the input signal.
The DC component is measured and subtracted from the measured composite
RMS value to obtain the RMS value of the AC component.
Resistance. To measure resistance, the DMM forces a current through the
unknown resistor and measures the voltage. The DMM IC computes the
resistance by measuring the voltage across the unknown resistor and dividing by
the current being forced.
When an open circuit condition exists, comparator (U35) detects the condition
and sets a latch, which is read by the readback register (U28). The DMM IC is
ignored and the open circuit condition is displayed.
Range changes are made by changing the magnitude of the current being forced.
The DMM IC does this by selecting different resistors in the current force circuit.
The resistors in the attenuation network for the voltage measurement mode are
used for this purpose.
THS720A MOD NV Component-Level Information Package
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Component-Level Theory of Operation
V oltage Reference. Voltage reference (U31) generates an accurate reference that is
used by the DMM circuits. The 2.5 V output is divided with four resistors to
supply the needed reference voltages.
CPU System
DMM Isolation.
The DMM is isolated from the rest of the main board. The
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digital signals are coupled through opto-couplers. Power is transformer coupled
from the isolated power supply
The CPU system contains a 68331 microprocessor (U6) that controls all
10
17
.
oscilloscope, DMM, and display activities.
CPU Clock. Processor clocks are derived from the 30.303 MHz oscillator that
drives the sampler (U7) and display controller IC (U21). The display controller
IC divides the 30.303 MHz clock by two for a processor clock of 15.15 MHz.
Interrupts. The 68331 supports seven levels of auto-vectored interrupts dedicated
to different interrupt levels. The sampler, display system, and DUART generate
interrupts.
Reset. The CPU resets both at power-on and power-off using the reset signal.
Reset controller (U3) controls system reset. Power-on reset asserts after the +5 V
supply stabilizes. Power-off reset asserts when the supply falls below a usable
threshold.
Memory. The memory subsystem includes flash ROM for power-off storage and
processor firmware. The memory system also includes dynamic RAM for use as
system RAM.
The flash ROM (U1)
is a 1 MB 8 device that provides nonvolatile storage
10
of front-panel settings, waveforms, and calibration constants. It also contains the
product firmware.
Dynamic RAM (U18)
is organized as 256 K 16 and provides of 512 KB
14
of system RAM.
Front Panel.
The front panel switch matrix is scanned by the CPU. The scan
12
signals are generated by (U13).
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THS720A MOD NV Component-Level Information Package
Display System
Component-Level Theory of Operation
RS-232. 13 Signals travel from the processor to the dual asynchronous receiver/
transmitter (DUART) (U4). The DUART sends data to the driver/receiver (U24).
U24 converts signals from logic levels on the DUART side to RS-232 levels at
the RJ-45 connector.
A raster display controller IC (U21) processes text and waveforms. The
14
display system sends the text and waveform information to the LCD display.
The primary functions of the display circuit is to write waveform data into
waveform planes and refresh the LCD display. The circuitry provides Vector,
Dot, Vector Accumulate, Dot Accumulate, XY, and YT display modes.
The display system provides text, graticule, and waveform bit planes. All
information displayed is first written to a plane. The bit planes are stored in a
dedicated DRAM (U17). The information is sent to the LCD display at a regular
refresh interval.
LCD Display
Main Power Supply
Battery and External
Power
The LCD display is a liquid-crystal display with a florescent backlight. Digital
data for the LCD is provided by the display controller. The AC voltage to power
the backlight is generated by the Inverter Board. The backlight intensity is set to
a fixed level that optimally balances brightness against battery life.
The main power supply provides DC power to non-isolated circuits on the
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Main board and to the isolated power supply. Power supply controller (U66) and
gate driver (U67) drive power transistor (Q15) through transformer (T6) to
generate +5V, –5V, and –25V DC.
Instrument power comes from either the internal battery or from an external
15
DC source. When you connect an AC adapter to the DC INPUT, the battery can
be charged. If an overvoltage is applied to the DC INPUT, SCR Q8 fires and
opens the self-healing poly-fuse F3.
The battery pack consists of four C-size NiCd cells. A low-battery condition is
detected by operational amplifier (U55) which sends a warning signal to the
CPU system.
THS720A MOD NV Component-Level Information Package
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