Revox A77 Service Manual

with open record volume control :
If noise occurs only with open record volume control, check
input amplifier.
Check Q 401 / 421 and Q 402 / 422.
Check tantalum capacitors.
Highs Playback Weak or Variable :
No Record :
Dirty magnetic heads.
Tape is not of type pre- scribed by manufacturer.
Wrong bias ( record equalization), see 6.5.2. to 6.6.
Playback head misadjusted, see 6.3.1.
Record head misadjusted, see 6.5.1.
Worn magnetic heads.
Check relays.
Check relay Q 601.
Replace oscillator.
Inadequate Erase : Dirty erase head.
Measure RF - voltage; if it is too low, check supply voltage
at oscillator.
Defective erase head.
Tape extremely over- modulated.
VU- Meter, None or Faulty Indication : Defective VU- meter.
Calibration misadjusted, P 504.
Switching Clicks :
RFI ( Radio Frequency Interference:
Transfer Play Sensitivity Too Low :
Defective rectifier D 351 - D 354 I VU- meter board 1.077.
4801.
Defective amplifier, Q 503 I record amplifier card 1.077.705)
see Modifications 8.2.
see Modifications 8.3.
see Modifications 8.4.
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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