Revox A77 Service Manual

Wow and Flutter : Mechanical causes :
Periodic wow and flutter whose origin is in a defective
pressure roller or whipping capstan axis can be recognized
by observing the rotating element's rythm ( pressure roller
or capstan axis might be marked with felt tip pen ). Pressure
roller, see also 4.4.1.
If rythm of wow is identical with the rotation of the left-
hand reel motor, the origin may be either mechanical or
electrical. The mechanical cause may be defective bearing
or misadjusted brake.
Electrical causes :
Overly strong counter torque of left-hand reel motor can
be cause for wow; check motor voltages, see table 5.9 — 46.
If wow occurs only at 3.75 ips, it may have its origin in too
large a distance of pick-up or in the regulation circuit, ( see
6.2.1 ).
Wow at both speeds may be caused by a defective capacitor
in the RC- network R 215/ C 209 in the regulation circuit.
Replace capacitor.
Inadequate Starting Behavior, Slow Rewind : Reels smaller than 60 mm ( 2 - 3/8" ) should not be used
if at all possible.
Optimum behavior can be expected only at nominal line
voltage.
Check reel motors with loosened brakes for light run ( axial
play of reel motors . 2 to . 3 mm ( . 008 to . 0J 2" ).
Increase R 125 to 1 or 1.2 kOhm.
Push Buttons Don't Hold : Dummy connector REMOTE CONTROL is missing.
End- of- tape switch is defectife, see 5.9.1, or strong light is
incident on photoresistor.
Check relay operating voltage ( 27 Vdc ).
End- of- Tape Switch Doesn't Function : Lamp defective. Check photoresistor and trigger, see 5.9.1.
37

Revox A77 Specifications

General

Wow and Flutter	0.08% (7 1⁄2 ips)
Frequency Response	30Hz to 20kHz (7 1⁄2 ips)
Signal to Noise Ratio	60dB
Type	Reel-to-Reel Tape Deck
Track System	4-track, 2-channel stereo/monaural
Reel Size	Up to 10.5 inch reel
Motor	2 x reel, 1 x capstan
Inputs	Mic, Line
Outputs	Line
Tape Speed	3 3⁄4 and 7 1⁄2 ips