Block Level Theory; Power Supply Assembly; Display Monitor Assembly - HP 54501A Service Manual

6-4. BLOCK LEVEL THEORY OF
OPERATION
The HP Model 54501A is a four-channel 100
MHz digitizing oscilloscope . The human inter-
face is a front-panel knob and keypad for in-
strument control and 9" (diagonal) green
phosphor CRT for information display .
Available on the rear panel is an HP-IB con-
nector for communication to a printer or from
a controller. Two oscilloscope outputs are
also available on the rear panel through BNC
connectors:
one for do calibration and one
for ac calibration and probe compensation .
The hardware of the HP 54501 A consists of
four main modules . Figure 6-1 is a simplified
block diagram of the four main assemblies .
Also, in the diagram are rear panel connectors
and the Intensity adjustment .
This manual supports troubleshooting to main
assembly level . Theory of operation for the
System Board Assembly is included for infor-
mation only and is not intended for
troubleshooting purposes .
6-5. Power Supply Assembly
The Power Supply Assembly of the HP 54501A
is a 120 W switching power supply . It has a
do output power connector and cable that
connects to the System Board Assembly . The
ac input range to the power supply is 115V or
230 V and has maximum power of 200 W
when operating at 48 - 66 Hz .
The Power Supply Assembly provides all vol-
tages necessary to operate the HP 54501A to
the System Board Assembly . Unfiltered vol-
tages of + 15V, -15V, +12V, -12V, +5 .15V, and
-5 .2V are supplied to the board where they are
then filtered and distributed throughout the
board and to the Display Monitor Assembly .
Filtered voltages of approximately +5 V and
+12 V are routed through the System Board
Assembly to the Display Monitor Assembly .
The +5 .15 V supply is adjustable . The adjust-
ment procedure is in section 4 of this manual .
6-6. Display Monitor Assembly
6-7 . System Board Assembly
HP 54501A SERVICE
The Display Monitor Assembly consists of the
sweep board circuitry, a 9-inch green phos-
phor display CRT, and the CRT yoke. The as-
sembly requires + 5 V and +12 V from the
power supply via the System Board Assembly .
The CRT is a non-interlacing raster display
controlled by the CPU portion of the System
Board Assembly . System control provides
synchronization and pixel information .
The System Board Assembly contains the ac-
quisition system and system control circuitry .
It also provides interfaces for the Power
Supply Assembly, Display Monitor Assembly,
keypad, RPG, and HP-IB . The input to the
System Board Assembly from the target sys-
tem is from any or all four channels located at
the front panel BNCs . The user interface is
from the front-panel keyboard or with a con-
troller via the HP-IB connector located on the
rear panel . A more detailed theory of the
System Board Assembly follows this block
level theory .
6-8 . Keypad and Knob Assembly
The front-panel keypad of the HP 54501A is
elastomeric and has 44 keys . Twenty of the
keys are single-function, 17 are dual-function,
and the remaining 7 are display softkeys with
variable functions depending on the displayed
menu . The keyboard rows are continually
scanned at a frequency of 60 Hz and when a
key is pressed, the signal is sent as data to the
68000 which determines the key pressed and
its function .
The RPG (Rotary Pulse Generator) is control-
led by the front-panel knob and supplies pul-
ses to the 68000 microprocessor when the
knob is turned . The RPG is used to dial in
values for various settings of the displayed
menu . The RPG will normally be set in coarse
mode but may be used in fine mode by press-
ing the front-panel toggle key above the RPG
labeled FINE .