Revox A77 Service Manual

9. TROUBLE SHOOTING
Pre - Check : Check network voltage.
Allowable deviation I also for short periods I at respective
settings of the voltage selector :
110 Vac : min 96 Vac, max 125 Vac
130 Vac : min 112 Vac, max 145 Vac
150 Vac : min 130 Vac, max 165 Vac
220 Vac : min 190 Vac, max 245 Vac
240 Vac : min 210 Vac, max 270 Vac
250 Vac : min 225 Vac, max 290 Vac
Use a regulator if the deviations are higher. Note that regul-
ators have a marked leakage field ( keep far from recorder ).
Check of regulated supply voltage 21 Vdc. Adjust on P 106
or replace diode D 104, if necessary.
9.1. Faults in the Drive
Capstan Motor fails to run : Check motor capacitor C 151.
Check regulation electronics, test points ( diagram 1.077.
725 ).
If the capstan motor does not start by itself after manual
stopping, the regulator pre- amplifier is oscillating. Exchange
R 206 ( 100 Ohm ) against 330 Ohm.
Check capstan bearings, exchange ball bearings against fac-
tory - new original ones.
Capstan motor rumbles : Exchange bearings against factory - new original ones.
Capstan motor whistles : Check gap rotor to pick-up I per 6.2.1 C. Put a strip of
rubber or equivalent between pick-up and its mounting
surface for vibration isolation.
Unpotted pick-ups are to be exchanged for potted ones.
Tape Speed too low : Check pick-up separation. Measure pick-up frequency ( per
6.2.2 I. Check regulation electronics, test points.
36

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