Ampex 351 - Page 60

BRAKE BAND REPLACEMENT
NOTE
Step 4:
Step 5:
Step 6:
Step 7:
Step 8:
Step 2:
Step 3:
Step 4:
6-12
If it is desired to measure capstan dig,
press the STOP button at this point
and select a piece of nylon lacing
twine about 30 inches long and tie the
ends together.
Slip the twine loop just formed be 
tween the idler and idler arm so that
the nylon rests against the idler shaft.
Attach the other side of the loop to
a 0 to 80 oz. scale, letting the nylon
twine remain slack.
Press the PLAY pushbutton, causing
the capstan idler to clamp against the
capstan.
Pull the scale away so that the nylon
twine is taut and makes a 90 degree
angle with the idler arm.
Now, slowly pull the scale away with
sufficient power to cause the capstan
idler to leave the capstan, reading the
scale at the instant the capstan idler
leaves the capstan. The scale reading
should be 5 lbs ±1/2 lb. If necessary,
adjust the capstan dig at the point
shown in the illustration.
Write the Service Department for a proper
authorized equipment return tag. Do NOT ship
unidentified parts to factory; Ampex can as 
sume no responsibility for their proper care
or return under such circumstances.
Brake Bands may be replaced without
removing motor from tape transport
on rackmount machines and deleting
the first three steps.
89-0131
89-0144
Issue A
CAUTION
Do not attempt complete disassembly
of any of the sub-assemblies. The list
of individually replaceable parts
under each assembly listing in the
parts list should be used as a guide to
disassembly limits. Replacement of
parts other than those listed calls for
precision work which should not be
attempted in the field. Assemblies
with defects in parts other than those
listed as replaceable should be re 
turned to the factory or to an Ampex
Authorized Service Center for repair
or replacement.
With a 7/16-inch socket wrench re 
move the four mounting nuts and
washers at the motor mounting
plate, carefully holding the motor
with one hand to prevent it from fall 
ing. The turntable will remain at 
tached to the motor assembly.
Take the motor to a convenient work
area.
Unhook the brake tension spring from
the brake lever.
Remove the two screws holding the
capacitor. Disconnect the capacitor
wires at the knife disconnects and
free the capacitor from the bracket.
Replacement of Parts
All sub-assemblies of the tape transport me 
chanism can be easily dismounted with the
use of a screwdriver and a few small socket 
head screw keys.
temperature of the capstan solenoid
will rise, and its d-c resistance will in 
crease. Therefore, the minimum line
voltage required to bottom the solen 
oid when it is hot will be greater than
that required when it is cold. If the
equipment is operating on unusually
low line voltage (below 100 to 105v),
sometimes encountered in areas
where regulation is poor, the solenoid
may fail to bottom after it has
reached normal operating tempera 
ture. It is advisable, therefore, to allow
the equipment to operate in the repro 
duce mode for about half an hour be 
fore making any necessary solenoid
adjustments. This will allow the
widest margin of safety with respect
to line voltage variations. The solen 
oid is factory-adjusted to bottom at 90
line volts cold and 105 line volts hot.
Step 3:
The most convenient method for changing
the brake band is first to remove the entire
motor assembly.
Step 1: