Handbook for Sound Engineers

Magnetic Recording and Playback 1089

head with the stick or core of the swab. Allow adequate
time, typically 30 s, for the solvent to evaporate before
rethreading the tape. You don’t want the leftover solvent
dissolving your recording tape.
Xylene head cleaning solvents will attack some plas-
tics including the lenses of optical sensors. Aggressive
solvents may either partially dissolve or create a hard,
glazed surface on some rubber rollers. If you notice a lot
of reside on your swab or rag after wiping a seemingly
clean roller, you are probably dissolving the roller, not
cleaning it! Use general- purpose cleaners for the plastic
components and rubber cleaners for the rubber rollers.
The tape must also be kept completely free of dirt.
Keep the surface of the transport clean to avoid dirt
being picked up during high-speed spooling. Always
return the tape to its storage carton between uses. Do
not stick your fingers through the windage cutouts in
the flanges of the reel and touch the edges of the tape
pack when handling the reel. (Skin debris from fingers
is a source of tape dropouts!) In addition:

1. Avoid eating greasy foods while handling tapes.


2. Contamination due to finger oils and debris can be
   avoided during editing sessions by wearing lint-free
   editing gloves, which are available at most camera
   supply stores.


3. Keep cigarette ashes and other powdery materials
   far away from the tape.

The cooling system of the tape recorder should be
cleaned periodically. Clean all air filters and cooling
passageways and remove any dust buildup with a
vacuum cleaner. Verify that all inlet or exhaust ports on
the bottom of the machine are not obstructed by
carpeting or dust and that adequate clearance for free
airflow exists at the rear of the machine.
Following cleaning, diagnostic servicing should
begin with verification that the tape guiding and tension
at the heads is adequate to maintain good tape-to-head
contact. Set aside one reel of tape, known as a shop tape
because it typically comes from the maintenance shop,
for testing. Run this tape in all modes while observing
the tape at the heads and the guides. The tape should not
run hard against either guide flange and there should
never be any edge distortion. If edge distortion is noted,
check for a bent guide or tension sensor arm. These
components can be easily bumped out of alignment by a
full reel of tape during loading or unloading.
On many machines a tape tension gauge of the type
shown in Fig. 28-56 can be inserted in the tape path
near the heads to measure the tension. For other
machines that are too crowded in the head area, either
the head assembly must be removed or a test location

away from the heads must be used. Measure the tension

at both the beginning and the end of the reel.

Note that the stiffness of a piece of tape varies with

the width, base film thickness, and type of tape. The

tension gauge must be adjusted before use to read

correctly for the specific tape sample being used on the

transport. A calibration weight is included with the

gauge for this purpose.

The following tape tension values indicate the range

of tensions commonly encountered on studio recorders.

The nominal value for a given model of recorder will be

found in the maintenance manual for the machine.

Some manufacturers specify tension measurements

with a spring scale and a cord that is wrapped around a

tape hub. Follow the recommended procedure.

Verify that the mechanical brakes or dynamic

braking logic is stopping the tape smoothly from all

modes and speeds without excessive force. A sticky

brake solenoid or dirty brake band can quickly ruin your

precious tape.

28.6.1 Speed

Absolute tape speed is extremely difficult to measure,

even under the controlled conditions of a laboratory.

One method available to maintenance personnel is to

measure the frequency reproduced from a commer-

cially available speed reference tape. The frequency

read on the frequency counter must be corrected for any

Figure 28-56. Tension measurement. Courtesy Ampex

Corp.

¼ inch 3–4 oz

½ inch 4–8 oz

1 inch 6–12 oz

2 inch 10–24 oz