HEWLETT PACKARD (HP) 141A
Service Manual

Section III p a r a g r a p h s 3-25 to 2-27 approach. The amplitude of the phenomena and the sweep-time required to display it will affect the p e r sistence. F o r example, with maximum PERSISTENCE and s o m e settings of INTENSITY, a single-shot straight-line t r a c e may bloom, Figure 3-4, and a single-shot signal with amplitude variations of s e v e r a l centimeters may not cause blooms, Figure 3-5. To determine the best INTENSITY setting, connect a signal which approximates the sweep time and amplitude of the single-shot signal to be written. Set PERSISTENCE fully clockwise and trigger a single sweep of the test signal. Set the INTENSITY as far clockwise as possible without causing blooming. Repeat the single sweep signal, erasing the display and setting the INTENSITY after each t r a c e until the des i r e d display is obtained. This setup should give maximum persistence to the single-shot display. After the single-shot signal has been written, turn the Presentation Selector to STORE to retain the display. 3-25. Single-shot signals which require a sweep time f a s t e r than 20 microseconds p e r centimeter can be written with m o r e brightness by setting the WRITING RATE to MAX. The s c r e e n w i l l be unevenly illuminated after erasing when WRITING RATE is in MAX, however the INTENSITY can be set high enough to make Note:

Model 141A the display visible through the illumination. A display, written with WRITING RATE s e t to MAX, will be obs c u r e d by positive fading more rapidly than a display written with WRITING RATE s e t to NORMAL. 3-26. Single-shot signals which require a sweep time between 200 and 20 microseconds per centimeter may have low brightness a t the centerof the screen. Fire a single-shot test signal with INTENSITY and PERSIS TENCE fully clockwise and WRITING RATE in NORMAL, and if the center brightness i s low, wait for one to three minutes f o r the low-brightness a r e a to become brighter. Likewise, if the entire- display brightness appears below a usable level, o r the display is not visible a t all, wait for one to five minutes for the display to appear, Figures 3-7 and 3-8. 3-27. F o r single-shot signals requiring a sweep time from one to five minutes, s e t PERSISTENCE and WRITING RATE to NORMAL and INTENSITY a s required to prevent blooms. F i r e the single-shot signal and after the sweep is completed, rotate Presentation Selector to VIEW and PERSISTENCE out of NORMAL. The complete display may then be viewed for up to one minute o r s t o r e d (Presentation Selector to STORE) for up to one hour.

A vertical amplifier plug-in, used in the horizontal compartment, may have less than specifiedbandwidth. Make the highfrequency adjustments (plug-in manual) with the amplifier in the horizontal compartments.

Figure 3 - 2 . Background illumination occurs when erasing with WRITING RATE in MAX

A

Figure 3-3.

Variable persistence with a slow, repetitive sweep

Figure 3 - 4 . Single-shot t r a c e bloom caused by INTENSITY and o r PERSISTENCE set too high

Figure 3-5. Single-shot display u i t h IXTENSITY and PERSISTENCE s e t the s a m e as Figure 3-3
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3-4