Roland Rhythm 77

The Roland Rhythm 77 drum machine was Roland's first product (formerly Ace electronics) - released in 1972. It is actually an updated and relabelled Rhythm Ace FR-8L
It was one of a trio of drum machines released by Roland that year, offering features intermediate between those of Rhythm 33 (TR-33) and Rhythm 55 (TR-55).
It comes in a flat wooden case with a metal base and has a holding for scorebooks - was dedicated to put at top of an organ for rhythm accompaniment.

Rhythms:

Latin: rhumba, beguine, cha-cha, mambo, samba 1&2, bossa nova, baion, bolero, tango
Rock: rock'n'roll 1&2, slow rock, ballad, western, march, jazz waltz, waltz, cancel (quiet)
2beat & 4beat: bass drum, snare, fox trot, swing, parade, shuffle

Instruments:

bass drum, snare drum, lo conga, low bongo, high bongo, rim shot, maracas, high hat, cymbal, tambourine, guiro, cow bell.
rim are used for metronome, too.
has a little mixer for: bass drum, snare drum, guiro, high hats.
has a tempo & volume fader; and a fade-out option :)
for start there's no button, it's a finger-sensitive touch-bar.
supports double tempo.
the power switch is not a primary AC-switch.

Some technical inside:

There's no IC inside - only one VCA...
Left: transformer, rectifier, softstart.
Mid: master clock, 5 dividers, reloop & down-beat LED, diode matrix.
The 1st divider is connected to the tempo-up switsch for a 1:1 or 1:2 ratio, the 2nd ones for switching between the 4/4 and 3/4 clock - 1:2 or 1:3 ratio.
Right: the voice board, mixer & output stage. BD, LC, LB, HB, rim are passive circuits.
Bottom: the rhythm switches...

External Sync

There's a little possibility to use din-sync on this device.
Logic board: leftest transistor, on its right the base resistor, solder on lower pin the clock line.
For start/stop - its like a pedal switch - just put a transistor serial into the male connector: gnd=emitter, top=collector, base=start/stop line.
Works best at 8 ppm clock, up-tempo off for best results. On up-tempo on the guiro & tambourine it sounds bad as they have a 2nd trigger input which they get from the 1st divider.

Had the idea for single-out for all mixable sounds - difficult to realize:you can keep the signal from the fader-in lines but they have to be aplified (opamp) - no prob.
Start/stop resets only the divider line - and toggles the output on/off by another flipflop to a vca (MFC 6040). this means, all 4 single-outs need a vca, too, the switch voltage can be chosen from the internal vca.