DEC DECtape 551 Manual page 61

NOTE: It may be necessary to replace one or both of the Type 1033
Attenuator modules with the jumpers in order to obtain the correct
ind ication spec ified in step 6. However, vernier adjustments shou Id
be made with both Type 1033 modules installed.
6. Observe the oscilloscope. The correct indication is a square wave with an amp-
litude of 6 to 7 volts and a pulse period of approximately 33.3 tJsec. If the correct
indication is not obtained, turn the sensitivity potentiometer {accessible through
the lower hole in the handle of the Type 4523 module} in one direction until a step
appears in the square wave as shown below. Turn the potentiometer in the opposite
direction until the step disappears and then reappears. Determine the adjustment
range of the potentiometer by rocking it between the two I im its wh ich produce a step
in the square wave. Permanently set the potentiometer to the center of this range.
f
6-7V
j
r- . . .
1---_ _ _
3,3.3
k
SEC _ _ _ _ --..
(A~OX)
-I
1 '1
u
'fit
11\
I (, 'I
TO
NOTE: The normal pulse period indicated in step 7 will vary with
the speed of the tape. Vernier measurements and adjustments
should be performed with the tape advancing in the forward direc-
tion.
7. Observe the oscilloscope. The duty cycle of the square wave should be 50%.
If the correct indication is not obta ined, then the duty cyc Ie potentiometer {ac-
cessible through the top hole in the handle of the Type 4523 module} must be ad-
justed. If an adjustment is made during this step, repeat steps 6 and 7 until the
correct indication for these steps is observed.
8. Return any Type 4523 modules, removed during the performance of this test pro-
cedure, to their original locations.
9. Remove both Type 1033 modu les and replace the jumpers at locations 1 A50 and 1 A55.
6-7