HEWLETT PACKARD (HP) 1707B
Service Manual

Model 1707B gates are both off at this time, the CRT remains blanked. At time t2, the delayed blanking gate closes. CR6 and CR8 turn on, CR7 and CR9 turn off, and R10 and R l 1 cease supplying current. Because current source 1 is supplying no current, the CRT turns on to maximum brightness. Although intensification is not needed in delayed sweep mode, maximum brightness usually is needed because the delayed sweep is a t a much faster rate than the main sweep. At time t3, the delayed blanking gate turns off. CR6 and CR8 turn off, CR7 and CR9 turn on, and both RIO and R11 supply current to blank the CRT. The events between t3 and t4 continue to take place but, because the CRT is turned off, are not seen. At t4, the main blanking gate opens. The next main sweep will reinitiate the entire cycle.

Theory are selected to fcause the correct CRT illumination in the various &odes. Current from A6A8R3 alone is sufficient to blank the CRT.
4- 114. l?stcrnal Horizontal Amplifier. The amplifier (schematic 15) consists of three cascaded differential rtmplifiers, a controlled current source and a single-

ended emitter follower output stage. The input of the first stage, FET differential amplifier A8Ql/Q2, is driven single-ended from the output of a compensated voltage divider consisting of A8R1, A8Cl/A8R2 and A8C2. The input circuit provides the required high impedance a n d voltage step-down. Voltage clamp A8CR1 and A8CR2 limits the voltage on the gate of A8Q1 between +15volts and -15 volts.
4-145. Differential amplifiers A8Q3/A8Q4 and A8Q5/A8Q6 are driven differentially from the output of A8Ql/A8Q2. The differential drive removes common mode noise from the signal waveforms and increases the amplifier bandpass.

4-139. Mixed Sweep Blanking Circuit. The mixed

sweep blanking circuit (schematic 15) consists of emitter follower A6A8Q1, enabling gate A6A8UlA, R-S flip-flop A6A8UlB/A6A8UlC, and transistor switch A6A8Q2. The purpose of the circuit is to turn A6A8Q2 on and off (mixed blanking gate in figure 4-4) a t the proper time. 4-140. In main sweep, the mixed sweep blanking circuit is held in a position that permanently turns A6A8CR7 off by the closed contacts of the SWEEP DISPLAY switch. 4-141. In the mixed sweep mode, A6A8Q2 is initially turned on. When the main sweep starts, the emitter of A6A8Q1 goes low and the enabling gate enables the R-S flip-flop. When the delayed sweep starts, delayed blanking goes low and the negative-going, leading-edge transition is differentiated by A6A8C3 and A6A8R9. The resulting pulse causes the flipflop to change states and A6A8Q2 turns off. When the main sweep terminates, the positive-going transition of the main blanking signal resets the R-S flip-flop in preparation for the next cycle. 4-142. Resistor A6A8R12 is connected to the -15volt power supply and supplies additional current to speed up switching.
4-143. Delayed Sweep Off. I n main sweep mode, (schematic 15) the operator has the option of having

4-146. Controlled current source A8U1 provides temperature compensation for the amplifier by maintaining equal currents into the two inputs. Normally, a change of current in A8Q6 will cause an opposite change in current in A8Q5 which, in turn, causes a change in the output voltage. When the current into A8U1 pin 1 changes, the current into A8U1 pin 8 changes a n equal amount and direction by action of the controlled current source. This change opposes the change in A8Q5 and thus provides compensation. 4-147. A8Q5 drives emitter follower A8Q7 which provides the required single-ended low impedance output. Amplifier gain is adjusted by varying horiz gain adj A8R15. A 10-to-1 gain ratio is provided by ext horiz VERNIER R6.
4-148.

GATE ASSEMBLY.

the main sweep intensified during the time the delayed sweep is in progress, or of disabling this feature. When the delayed sweep is set to OFF, A6A8CR10 is grounded. This permanently turns A6A8CR9 off while in this mode of operation. Because the closed contacts of the sweep display switch cause A6A8CR7 to be off at all times in main sweep mode, A6A8R3 is the only source of blanking current in main sweeD with delayed sweep set to OFF. The values of A6A8R3, A6A8R10, alid A6A8Rll

4-149. The gate assembly (schematic 17) combines (sums) inputs from five different sources and controls the brightness of the CRT. The basic input is the current sink consisting of A4R3, INTENSITY potentiometer R1, and the -15-volt power supply. The current sink draws current from one or more sources. The basic source is A4Q1. The amount of current drawn from A4Q1 depends on the setting of the INTENSITY potentiometer. The amount of current drawn &om A4Q1, in turn, controls the brightness of the CRT. 4-150. When the BEAM FINDER switch is pressed, A4CR8 and A4R1 are connected in parallel with the current sink, causing it to demand more current. This causes the CRT to turn on with maximum intensity. 4-151. When the Z AXIS INPUT is connected to a voltage source, A4R2 and the voltage are in parallel 4-13