STROBOTRON DOES NOT FLASH.

4.5.7 STROBOTRON DOES NOT FLASH.

If the strobotron lamp will not flash, but the pilot light is on:

a. Check that the range switch is not in one of the EXT INPUT

positions.

b. Turn the instrument off and turn it on again after 10 seconds.

The thyratron may hold over if the instrument is in an EXT INPUT posi -

tion when a plug is inserted in the INPUT jack.

c. Make certain the strobotron is firmly seated in the lamp socket

(refer to WARNING paragraph 4.4.5).

d. Check power -supply voltages (+250V, +400V, and -400V).

e. Replace V1 (5965) or V2 (5727).

4.5.8 STROBOTRON FLASHES ERRATICALLY.

If the strobotron lamp arcs at the base, the lamp is at the end of

its useful life and should be replaced.

a. If the strobotron fires erratically when the stroboscope is

triggered from an external contactor, the trouble may be due to con-

tact bounce at the contactor contacts.

b. If the strobotron lamp flashes at the same rate, regardless

of the RPM dial setting on all three speed ranges, potentiometer R3

(see Figure 4-1) is probably open-circuited.

c. If erratic firing continues, the trouble is probably due to hold

over and the strobotron lamp should be replaced.

4.5.9 NO INDICATION FROM CALIBRATION LAMP.

If the stroboscope flashes, but the CAL indicator lamp remains

out when the HIGH CAL and LOW CAL settings are adjusted (see Fig-

ures 4-1 and 4-2):

a. The CAL indicator neon lamp V5 may be defective. Remove

the instrument from its case and then remove the two screws that se -

cure the lamp holder to the instrument panel. Unsolder the lamp from

the terminals and replace with a new lamp.

b. The neon lamp V4 may be defective. Unsolder the lamp from

the etched board and replace with a new lamp.

C. Capacitor C3, or resistor R22, R23, R24, or R29 may be

defective. Replace if necessary.

4.5.10 INSTRUMENT CANNOT BE CALIBRATED.

If the stroboscope cannot be calibrated by following instructions

given in Section 2, OPERATING PROCEDURE, see Figures 4-1 and 4-2,

and check the following:

a. Tube VI (5965) may be defective. Replace if necessary.

b. If the unit cannot be calibrated at either the 3600 RPM or 900

RPM positions, check rheostats R1 and R5, and resistors R2 and R6 for

proper values.