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Factory service manuals show a machine as line drawings. Line drawings are unambiguous, which is their virtue, and they are nothing like what you actually see when you take the lid off a recorder that has been sitting in a room for forty years.
These are photographs of one Revox A77 taken through a complete disassembly, in the order the factory manual sets out. Every part number quoted here can be looked up in the A77 parts reference.
The photographs are free to copy and reuse, including commercially, provided Kuon R&D is named. See the terms. If you are documenting one of these machines yourself, take them and use them.
The two machines you are likely to meet
The A77 ran from 1967 into the late 1970s and changed as it went. The front panel is the quickest tell: earlier machines carry a silver panel with the script logo, later ones a grey panel with the squared logo. Underneath, the changes that matter to a restorer are the head fastening and the head block, and those are covered in the parts reference.
Before anything is unscrewed
The plate on this machine reads Type A77, serial G 38508, 110 to 250 volts, 50 to 60 hertz, 80 watts, made in Germany by Willi Studer GmbH. That last line is worth noticing: not every A77 was assembled in Switzerland.
The black drum beside it is the mains voltage selector, marked 110, 130, 150, 220, 240 and 250. It is set by rotating it to the figure you want. The fuse changes with it, and the plate states both: 1 AT for the 110 to 150 volt range, 0.5 AT for 220 to 250.
This is the first thing to check on a machine bought from another country, and the most common way to destroy one on the first day of ownership.
Removing the cover panel
The bank of sprung contacts running left to right is the switch assembly the transport buttons operate. It is mechanical, it is accessible, and it is one of the reasons these machines can still be repaired: nothing here is a sealed module.
The two small levers at the front, marked SPEAKERS OFF and REEL MOTORS OFF, are the bar switch, part number 1.077.355-03.
Removing the front panel
The arrows on this photograph were drawn on the day, not afterwards. The front panel is held by one screw at each end, and once those are out the panel comes away along the line marked in yellow. The factory manual covers this as section 3.3, in three sentences and no picture of an actual machine.
The tape path and the head block
Left to right: the tape guide cup (1.736.222-04) and collar (1.736.222-05), the shielded erase, record and playback heads, then the capstan shaft with the pinch roller (1.077.312) on its lever.
The head shields are where the two-hole and one-hole fastenings diverge. Two-hole shields are 1.077.155-03 and -04, one-hole are -05 and -06, and the heads themselves change with them. Search for Head in the parts reference and the pairs sit next to one another.
The chassis out of its cabinet
This is the whole transport as one object. The two aluminium discs at the top are the reel motors (1.077.280). Below and between them sit the brake levers (1.077.410 and 1.077.415) with their springs, working on the brake drums (1.077.561) through the brake bands (1.077.421). The four-digit mechanical counter is in the middle. The capstan and its flywheel are below that.
Everything visible here comes apart with hand tools and everything visible here has a part number.
The rear: transformer, motors and the card cage
The row of boards along the bottom edge is the card cage. Each card lifts out on its own, and each has an order number: input amplifier 1.077.700, record amplifier 1.077.705, oscillator 1.077.712, record relay 1.077.715, playback amplifier 1.077.720, loudspeaker amplifier 1.077.850, speed control 1.077.725.
Knowing which card is which is most of fault-finding on this machine. The full list is in the parts reference.
The power supply
The yellow blocks are what a correctly re-capped mains side looks like. They are X2 class safety capacitors, 0.047 microfarad, 310 volts AC, with a date code of 2015 on them, and they sit where the originals were.
This matters more than any other single job on a machine of this age. The original mains-side film capacitors fail, and they fail loudly, usually on the first power-up after a long rest. Replace them before you switch on, not after, and use parts carrying a proper X2 marking rather than a general purpose film capacitor of the same value.
Cabinet, transformer and motors
The capstan motor is 1.077.200 as an assembly, and its internals are listed separately: rotor, thrust bearing, felt rings, belleville springs. The felt rings (1.077.220-01) and the plastic caps (1.077.220-02) are the parts that are actually consumed.
Working on the bench
Back in service
That is the point of all of it. A recorder built before most of the people now repairing them were born, put back into daily use, with tape running through it.
If you are documenting one of these
This archive is incomplete and will stay incomplete, because no single machine shows every variant. If you photograph something that is missing here, or confirm a part number that this list gets wrong, send it. It will be credited to you and added.
These recorders were made in tens of thousands and are now scattered in ones and twos across the world, each with somebody working on it alone. The documentation is the only thing that connects them.