This is a rather bizarre unit with an organ on the bass octave and a third. It gets layered with various tones depending on what you select in the solo section...though not always the solo sounds. Also a rhythm generator chip is used to create half a dozen patterns it appears. Preset voices are very interesting as you can witness in my video . There are boards for the solo on the upper left, bass on the bottom left, tone generation for organ I assume on upper right and other things in there. Mostly transistor and op amps and a few digital chips. Leading edge in 1974! Surely one of the earliest mitsubishi output modules! It uses the dual TOS chips as noted above and a lot of tank circuits to generate rhythm tones etc. Fascinating unit. A lot of character built into a few presets and a nice solo synth set of parameters.
I also give an overview of the likely repair issues in the video above. Boards are labelled on stickers inside unless they've fallen off. Solder joints as I note are always bad on interconnects and the power module. Work them over before even starting. Haven't seen a bad capacitor yet but one leg broke on one.
Someone asked about the details on the rhythm pattern generation chip K072265. I can't find a document on it but here is the text from the manual that describes what various pins do on it anyway... I just typed in the whole section on pattern generation and rhythm sound generation actually:
The Rhythm unit is a fourth independent tone generation system. It consists of a pattern Generator board and the instrument generator board, and provides six continuously running automatic rhythms. The unit can strum the accomp note/chords, gate the bass and alternate fifth synchronizing with the downbeat, privide a synchronous pulse to the WA-WA on Hill Band, and a down-beat pulse on the Bag Pipe.
The Rhythm Instrument Generator board is mounted immediately behind the accomp keys. It provides bass drum, conga drum, clave, snare drum, maracas and brushed cymbal voices when driven by synchronized positive pulses from the pattern generator. Additional circuits are a down-beat light driver, accompaniment modulator strummer driver, white noise generator, +24V and +18V regulators, and the instrument post amplifier and level control.
The white noise gen. develops a broad spectrum random noise in a back biased base emitter junction of D1013. It is coupled through C1017 to noise level control R1046, amplified by Q1007, and coupled to the brush cymbal, maracas, and snare drum circuits where it will become part of those voices.
The brushed cymbal sounds when a positive drive pulse from the pattern generator drives Q1010 ON, developing a positive pulse in it's emitter charging C1030 through D1016. This positive pulse biases D1014 and Q1012 ON allowing white noise to be amplified by Q1012 where it is voiced by L1001, C1027 and R1073 and passed to the post amplifier.
THe Maracas uses a similar circuit with shorter time constants in the gating circuit producing a shorter burst of white noise.
The snare drum is produced by a positive enabling pulse supplied to Q1013 turning it ON. The positive pulse developed in it's emitter passes through D1020 to charge C1043 in the gate of Q1014, biasing this FET ON briefly. This puls also couples through D1019 to excite tank circuit L1002 and Q1040, producing a damped oscillation which becomes the head sound of the snare drum signal. The excitation pulse to the tank circuit also gates D1018 to allow white noise to mix with the damped oscillations at the source of Q1014 and the combined signal passes through Q1014 to the post amp while the gate circuit is biased ON.
The Clave signal is produced by a positive enabling pulse turning Q1015 ON which excites ringing circuit L1003 abd C1049. The oscillations produced are coupled through mixing resistor R1108 to the post amplifier.
The conga drum is produced by direct positive enabling pulse through D1021 which exites L1004 and C1052 ringing circuit producing oscillations which couple through mixing resistor R1112 to the post amplifier.
The bass drum is produced by a positive enabling pulse coupled through D1022 and excites L1005 and C1056 into oscillation. This signal couples through amplifier Q1016 and to the post amplifier.
Downbeat light driver Q1005 receives positive pulse from chip pin 17 which drive the Darlington Transistor into heavy conduction illuminating the Downbeat LED D1011. Note that the downbeat light and entire rhythm unit clock system operates continuously.
The Strummer function modulates the accompaniment keyed notes when either the strummer or strummer rhythm buttons are depressed. Pattern generator chip pin 19 supplies timed pulses to Q1006 if either of the above mentioned switches are depressed. The pulsed heavy conduction of Q1006 causes illumination of accompaniment photo-modulator M800 permitting keyed accompaniment note 5 or or chords to pass through. If neither strummer switch is depressed the adjustment of R1042, Non-Strum accomp level control, sets the operating level of Q1006 so that the accomp photo-modulator is partially illuminated and a controlled level of accompaniment signal passes.
Two VR circuits are included on the instrument gen. board. +31V from the main power supply enters the board at pin A7 where it couples to the +24V regulator comprised of 11V Zener D1009, Q1003 and Q1002. The +24V provides B+ for the pattern generator, bass keying as the source of power for the +18V regulator, Q1004. The +18V is further reduced by a voltage divider to +9V for the instrument gen. circuits.
THE PATTERN GENERATOR BOARD:
The Pattern Gen Board is located immediately behind the accomp keys. The LSI Chip is the major component on the board and is soldered into the board. (then they tell you to swap the board if it fails... P/N 72165-8. Good luck finding that. haha -editor's note)
A clock circuit is contained within the chip with control brought out on pins 2 and 39. Selected value component and associated resistors with Tempo Control R1001 control the operating speed of the clock. Rhythm addressing lines from chip pins 33-38 are switched to ground by the rhythm selector switches to enable the ROM to generate appropriate pattern for the instrument board.
The clock functions at a normal 48 count period except when in Waltz or Fox Trot are selected +24V is supplied to chip pin 28 to change the period to 36 counts. The chip will generate patterns only if the chip pin 15 is grounded, provided either the Organ Rhythm or Strummer Rhythm switch is depressed.
Chip pin 19 supplies modulator trigger pulses to the Strummer and Strummer rhythm switches which if depressed send these pulses to Q1006 to strumt he accompaniment audio signal. Chip pin 17 supplies pulses to the downbeat light driver, and to Bag pipe accomp detuning on Solo/accomp generator board and to accomp pulse amplifier Q713 on the bass generator board. Q713 will function as an amplifier if its collector is not grounded through Organ and Organ Rhythm switches, and will pulse a keyed bass note through Q708. Chip pin 4 receives an enabling pulse voltage when a bass note is keyed so that if a strummer function is selected the first note sounded from the bass will be a root and the alternate fifth enabling pulse will appear at chip pin 9 during the next interval.
I have a used left control panel and some boards! Lots of generic parts. Ask if you need a specific part but I do NOT have the output module.
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