HEWLETT PACKARD (HP) 122A
Service Manual

M o(jel 122A
4-1

Sect. IV Page 11

COMPLETE ADJUSTMENT PROCEDURE

usuially a particular oscilloscope will not need
coniplete testing and calibration. Only one or two test:s will be needed and they can be done without conipleting the entire test procedure. following procedures are listed in a recomThe! a merided sequence for complete test and calibraoperation. In general, tubes are the main tionI se of trouble and new ones should be tried cau, befcire making adjustments or component replacemerits. See paragraph 4-4. SPE3CIFICATIONS FOR THE @ MODEL 122A OSCIL,LOSCOPE ARE GIVEN IN THE FRONT OF THIS MA: NUAL. THE FOLLOWING TEST PROCEDURE COTgTAINS EXTRA CHECKS TO HELP YOU ANAL' f Z E A PARTICULAR INSTRUMENT. THESE EX' TRA CHECKS AND THE DATA THEY CONTAIN CAIVNOT BE CONSIDERED AS SPECIFICATIONS.

3) Turn instrument on and measure the output voltage of the internal power supplies (see paragraph 4-9 POWER SUPPLIES). When turning the oscilloscope on for the first time after repair in any power supply circuit, turn the INTENSITY control fully counterclockwise before applying power. Failu r e to follow this precaution may cause permanent cathode-ray tube damage. If you are able to get a small, round, and sharply focused spot with good brilliance by adjusting the controls, the high voltage power supply can be assumed to be operating properly.
4) If necessary, the high voltage can be measured and adjusted as in paragraph 4-8. If R308, High Voltage Adjustment, is changed, adjust FOCUS and Astigmatism (R316) controls at low intensity toobtain a small, round, and sharply focused spot. If the high voltage is changed, recalibrate the Vertical and Horizontal Amplifier Gain.

For' location of the controls mentioned in the follow:ing procedure, see Figures 4-1, 4-2 and the VOlltage and Resistance Diagram at the end of this secition. A fifteen minute warm-up and power SUP1 ply output voltage measurements are always recc2mmended before making any other test or adjListment

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5) If the cathode-ray tube physical position has been changed, check trace alignment with bezel. Turn TRIGGER LEVEL control fully counterclockwise to AUTO. Set SWEEP TIME switch to 50 MICROSECONDS/CM. The CRT trace should be parallel with the graticule lines. The CRT face should be placed just behind the filter in the bezel. If CRT face and filter touch, a visible interference pattern will result.

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T U R N ON PROCEDURE

Perform this procedure only after repair work has been done on the instrument. The purpose of tllis procedure is to check that none of the power SUP1Jlies have been shorted and to s e r v e as a partial rhpi -..-:k upon the correctness of the repairs that have been made.
1) Measure resistances from the power supplies to ground. When measured with an @Model 410B Voltmeter, they should be within 50%of the following:
+ 380 volt supply + 100

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P O W E R SUPPLIES

The power supplies in the oscilloscope are extremely stable and will require infrequent adjustment. The output voltages should be measured with a recently calibrated 1%voltmeter, such as an @Model 405A or 412A, a t regular intervals but unnecessary adjustments should be avoided. CAUTION When first turning the oscilloscope on turn the INTENSITY control fully counterclockwise before applying power. Failure to follow this precaution can cause permanent cathode-ray tube damage.

-150 + 24

50K ohms 50K 12K 5.5K (Remove V1, 2, 4, and 5 to check)

2) Measure resistances to ground into the vertical and horizontal input terminals for all dc switch positions. As measured with an @Model 410B Voltmeter these resistances should read: VERT SENSITIVITY = 1 Megohm OFF = a CAL =a, HORIZ SENSITIVITY I1 Megohm

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1) Turn instrument on and allow at'least 15 minutes for warm-up. 2) Turn the sweep generator off by turning the SWEEP TIME HORIZ SENS switch to 10 VOLTS/ CM.

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