SECTION 3
CIRCUIT DESCRIPTION
General Information
Fig. 3-1 is a block diagram of the Type TU-7 Plug-In Test
Unit. The circuitry of the unit may be separated into three
major divisions: the Power Supply Loading Circuit, the Dual-
Trace Switching Circuit, and the Pulse Generator Circuit.
All three of these circuits are controlled by TEST FUNCTION
switch SW10,
POWER SUPPLY LOADING CIRCUIT
General Operation
The purpose of this circuit is to operate the regulated
power supplies of the oscilloscope under extreme load condi
tions to determine if they regulate properly. Fixed-resistor
dummy loads are used to simulate the loading effect of
plug-in preamplifiers. The LOW LOAD and HIGH LOAD
positions of the TEST FUNCTION switch are used to con
nect the correct loads to the low-voltage power supplies.
The GAIN SET position provides a check of the gain of the
oscilloscope vertical amplifier. The COMMON MODE posi
tion of the switch provides a check of the oscilloscope verti
cal amplifier rejection ratio. The last four positions of the
TEST FUNCTION switch operate the dual-trace switching
circuit or the pulse generator circuit and will be discussed
under those headings.
Detailed Description
When TEST FUNCTION SW10 is set to the LOW LOAD
position, the main load on the —150-volt supply is provided
through R125, with slight additional loading through the
dual-trace switching multivibrator circuit. The + 100-volt
supply is loaded primarily by R121, R124, R18, and R19, with
additional loading through R85 and R86. Minimum loading
for the +225-volt supply is provided by R122, as well as
the resistors in the vertical position network, R80A,B,C,D, R81
and R82. The +350-volt supply receives no load in the
LOW LOAD position. All of the minimum load resistances
remain in the circuit at all times.
When the TEST FUNCTION switch is set to the HIGH
LOAD position, additional dummy load resistors are con
nected to ail four low-voltage power supplies. R116 loads
the — 150 volt supply; R ill and R112 in parallel load the
+ 100-volt supply; R109 and R110 in parallel load the -f-225-
volt supply; and R106 and R107 in parallel load the + 350-
volt supply.
Pins 1 and 3 of the interconnecting plug are the input
signal and vertical positioning connections for the oscillo-
3-1
Fig. 3 -1 . Type TU -7 Block D iagram .
