IBM 727 Manual Of Instruction page 61

NOTE: When removing the tape break light bulb, care must be taken to return
the special washer which is located between the bulb and its socket.
not remain in place within the assembly without the washer.
1 5.9 .8 Write Current Measurement
The write current should be indicated by a reading of 56v ± 5v measured across
the 5. lk-ohm resistor at test points A4 and A8 of each track.
sistor of the LTro.
W it
15.9 .9 Read Circuits
When observing normal tape read signals, look for a sufficient gain to be avail­
able to obtain 22v peak to peak at the read bus.
be set for 20v peak to peak at the read bus observed on an oscilloscope.
of tape of known quality. Write l fs in all tracks, and then read this same tape when
setting the gain potentiometers.
There is no master tape for comparing the amplitude of all tape drives to a
standard. The limits of the tape drives are broad enough to handle any normal varia­
tions of signal amplitude of tapes written on one machine and read on a different ma­
chine.
15.9.10 Reel-Hub Shimming Adjustment
When the reel-hub knob is turned in a clockwise direction from the front of the
machine, the steel cover over the reel is forced to the rear and the diameter of the
rubber ring is expanded about the circum ference of the reel.
panded sufficiently, removal of the reel is prevented. However, if the rubber ring
is allowed to e^qpand too much there is a possibility of placing a permanent bow in
the steel cover. A lso, damage may result to the reel and rubber ring.
Shims (P/N 1091333) are placed between the knob and the hub assembly to pre­
vent too much tightening of the knob.
Take the following steps when shimming the assembly:
1. Assemble a minimum of 24 shims.
2. Place the gage (P /N 460798) over hub.
3. Remove one shim and tighten knob.
4. Attempt to remove the gage by grasping it firm ly with two hands and applying
a steady force parallel to the axis of the shaft.
5. Continue to rem ove one shim at a time until the gage cannot be removed.
6. Add one shim at a time until the gage can be removed easily.
7. Note the number of shims at completion of step 6 and subtract four to obtain
the quantity of shims required.
This is the cathode r e ­
The gain potentiometers should then
When the ring is ex­
61
The bulb will
Use a reel