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Section I: Precautionary Measures

In the Mini-Moog, as in any electrical device, shock hazards exist. All lethal voltages are confined to the area around the power switch and the A.C. fuseholder. Always unplug the instrument while servicing the electronics. Keyboard cleaning and adjusting may be done with the unit turned on.

When a fuse blows, replace it only with the proper size as indicated on the label directly below the fuseholder. If the fuse continues to blow, it is an indication that a definite electrical problem has developed. Never try a larger fuse; this will only result in further internal damage.

Avoid making adjustments at random. Each adjustment is critical and should be made in accordance with the procedures outlined herein. If a sub-assembly is found to be defective, we recommend exchanging it rather than attempting to repair it. Unless a qualified technician is available, with special test fixtures, more harm than good may result and possibly void any remaining warranty.

Section II: Sub-assembly Description

93-113 Oscillator (Board 1)

This assembly contains three tone oscillators, summing amplifiers, exponential current generators, waveshaping circuits and a -5 volt reference source. The three oscillators are independent and non-synchronous. Each oscillator is voltage controlled from external sources such as the keyboard. Linear input voltages are converted to exponential currents which are used to control the frequency or pitch of the tone produced. The basic sawtooth signal is processed to derive triangle and variable width rectangular waveforms. Oscillator #3 has a wide range capability which enables it to be used for modulation purposes. The -5 volt reference source is used to establish the precise voltage steps on the octave range switches.

93-114 Contour Generator (Board 2)

This assembly contains two identical contour or envelope generators, and the keyboard circuitry. Upon triggering, the contour generators produce a voltage envelope with variable attack, decay, and sustain. The output is used to control the gain of the first voltage controlled amplifier or the cutoff frequency of the voltage controlled filter.

The keyboard circuit contains a constant current source which feeds the keyboard resistor string. This insures the proper voltage drop across each of the 43 keyboard resistors. Also contained on this assembly is the sample-hold circuit which measures the voltage from the keyboard and maintains it until a different key is depressed. The output of this circuit is the control voltage for the oscillators and the filter. The glide feature is a function of the sample-hold circuit.

93-115 Power Supply (Board 3)

This assembly contains the plus and minus 10 volt regulators, the headphone amplifier, the noise generator and the modulation mix amplifier. The plus supply uses a temperature compensated zener diode for a voltage reference. The minus supply is referenced to the regulated plus voltage causing the two supplies to "track". Both supplies employ remote voltage sensing for optimum stability.

The headphone amplifier is an A.C. coupled emitter follower with a push-pull output. The noise generator uses a reverse biased transistor junction for a noise source. The output of this transistor is processed through three filter circuits to derive the white, pink, and red noise outputs. The modulation mix amplifier takes signals from Oscillator #3 and the noise generator, sums them and supplies an output which is used for modulation.

93-116 Filter (Board 4)

This assembly contains the voltage controlled filter, the external input pre-amplifier, the overload lamp driver, the first and second voltage controlled amplifiers and the A-440 reference oscillator. The filter is a voltage controlled low pass type which employs the Moog patented ladder network. It is capable of regenerating (oscillating) over a wide frequency range. The scale is adjustable so the filter can be set to track the keyboard.

The external pre-amp is a three transistor high-gain amplifier. The output of the pre-amp is monitored by an overload indicator. The overload driver circuit is a Schmitt trigger which turns the overload light on when external signal levels become excessive.

The first and second voltage controlled amplifiers are two nearly identical circuits. Their gain is controlled by varying the voltage which supplies the current source transistors. A buffer or output amplifier follows the second VCA stage.

The A-440 reference source is a highly stable Wein Bridge oscillator circuit. It produces a somewhat imperfect sinewave which increases its harmonic content. These harmonics or overtones assist in tuning to the reference, especially when the source being tuned is one or two octaves away from the reference frequency. The output of this circuit is coupled to the VCA buffer amplifier.

93-118 Rectifier Board

This assembly contains the input bridge rectifier diodes and the unregulated D.C. filter capacitors.

93-060 Left Hand Controller

This assembly contains the PITCH wheel, MODULATION wheel, GLIDE and DECAY switches, and two jacks for remote switching of glide and decay. The PITCH wheel has a mechanical detent which allows it to be easily returned to a pre-set tune point.

To service this assembly, remove the two mounting screws and lift the unit out. All connections to this assembly are through a 12 prong plug to simplify servicing and replacement.

93-061 Keyboard

The Mini-Moog keyboard is a standard three and one-half octave removable sub-assembly. All electrical contacts are gold plated for high reliability. The keyboard is held in place by four (4) mounting screws which are accessible when the bottom cover is removed. All connections to this assembly are through a 6 prong plug to simplify servicing and replacement.

Section III: Block Diagram

(This block diagram is a simplified version of the one from the User's Manual. The diagram from the service manual fits on a single 11"x17" sheet.)

Section IV: Trouble Analysis Guide

Use this chart along with the block diagram (Section III) to determine which assembly or component is defective.

Section V: Sub-Assembly Locations

In order to service the Mini-Moog circuitry, it is necessary to remove the rear cover assembly.

Remove 18 screws (5 top, 5 lower back, and 4 each end of cover); then lift the cover off.

Circuit boards are plugged into sockets at the bottom and secured at the top with two mounting screws. To remove a circuit board, first remove the screws then unplug from the connector.

When replacing, be sure board is firmly seated in the connector before tightening the mounting screws. Remember to re-install the fiber washers between the boards and the frame.

After board replacement, refer to Section VII: Adjustment Procedures and Locations, to determine which adjustments should be made.

Section VII: Adjustment Procedures and Locations

Each time a Mini-Moog is serviced, it should be tuned. When a board has been replaced it will be necessary to make additional adjustments. Refer to the table below to determine which adjustments must be made according to the board that has been replaced.

ADJUSTMENT PROCEDURES

NOTE:

The tuning and other functions rely heavily on accurate power supply voltages.

Always be sure the + and - 10 volt supplies are properly set before making other adjustments.

* Digital voltmeter with 0.1% accuracy

93-113 Oscillator: Adjustment Locations

93-115 Power Supply: Adjustment Locations

Section VIII: Keyboard Maintenance

Occasionally it will become necessary to clean and adjust the keyboard. The contacts, although gold plated, may become dirty, contaminated, or corroded. When contacts become poor, noises and erratic sounds may be generated while playing the instrument.

To service the keyboard, the bottom cover must be removed. This cover is held on with 8 wood screws. If the keyboard compartment is found to be excessively dirty, it should be blown out with air first.

Avoid touching the buss bars or the spring contacts with the fingers since hand oils and perspiration will cause corrosion. Under normal conditions, any dirt can be removed by spraying the assembly with a light coating of a high grade contact cleaner. At the factory, we use and recommend Cramolin®. If this is not available, TV tuner spray may be used. Do not under any circumstances use abrasives or abrasive tools, since this will destroy the gold plating. If spraying does not cure the problem, try wiping the buss bar with a cotton swab in the area of the problem key or keys.

Sometimes it is necessary to adjust the spring contacts for more tension. This is done by bending the spring so that it is closer to the buss bar. It is easiest to bend at the end nearest the mounting board. In all cases, the "pitch" contact must occur before the "trigger" contact. The pitch buss bar is nearest the front of the instrument. The trigger buss bar is in the center, and the third buss bar nearest the rear of the instrument is not used and therefore need not be cleaned or adjusted.

To clean the keys, use a soft cloth moistened with a mild soap solution. Never allow solutions or spray cleaners to run down between the keys. Avoid harsh solvents, since the keys are made of plastic and may be dissolved. Scratches may be removed with a plastic or automotive polishing compound. Waxing the keys is not recommended.

Section IX: Schematics

(The circuit schematics are not available at this time.)

Section X: Component Locations

(The component location diagrams are not available at this time.)

Section XI: Replacement Parts

* Order unlisted parts by description

Section XII: Modifications

93-113 Oscillator Assembly (Board 1)

To improve tracking and pitch stability on Mini-Moog oscillator boards with serial numbers above 1300, make the following changes:

1. Change R-69, R-105, and R-141 from 6.8K to 15K 1/2 W 5% carbon
2. Replace R-78, R-106, and R-128 with RC Network, part number 65-032
3. Change R-181 from 56K to 51K 1/2 W 5% carbon
4. Change R-170 from 15K 5% to 15K 1% Metal Film
5. Change R-162 from 3K 5% to 3.01K 1% Metal Film
6. Change C-3, C-5, and C-7 from 47 pf to 100 pf

All parts listed above are available in kit form, part number 94-001.

93-114 Contour Generator Assembly (Board 2)

To reduce thumping which may occur when a key is depressed, add a 10 pF capacitor from pin 4B to pin 5B on the Contour Generator board.

93-115 Power Supply Assembly (Board 3)

To reduce oscillator bleed through and cross modulation, replace 10 ohm resistor next to the "+1"0 V ADJ trimpot with a straight wire. Be sure wire does not touch the body of "+1"0 V ADJ trimpot.

93-116 Filter Assembly (Board 4)

To reduce intermodulation distortion which occurs when mixing two or more signals:

1. Change R2 from 47K ohms to 160K ohms
2. Change R8 and R28 from 27 ohms to 4.7 ohms
3. Change R40 from 1K ohms to 10K ohms

Section XIII: Ordering and Shipping Instructions

Ordering Parts

Most commonly used parts are listed in Section XI. When ordering, please include the Moog part number. If the part is not listed, order by description. Be as accurate as possible when describing what you want.

Example:
Transistor, Q8 on board 2
or
Control, amount of contour

Returning Parts

All parts being returned should be accompanied with a "Return Material Tag". Eight of these tags are supplied with this manual; additional tags are free upon request. Fill the tag out as neatly and accurately as possible. Package the part being returned so that it will not be damaged in shipment. Circuit boards should be double wrapped and enclosed in a rigid cardboard box. Attach the "Return Material Tag" to the part, not to the shipping carton. If the entire unit is being returned, it must be shipped in the original carton.

Address

Use the following address for all orders and returns:

Moog Music, Inc.
Academy Street P.O. Box 131
Williamsville, New York 14221

MOOG MUSIC, INC.

SERVICE DEPARTMENT POLICY

MINIMUM CHARGE (for non-warranty service) ­ is 1 hour ($15.00). Additional charge per 1/2 hour ($7.50). Update parts are free; all other parts are charged to the customer.

WARRANTY ON REPAIR ­ is issued as of date stamped on pink copy; only for parts or malfunction repaired. Warranty period is 90 days­we pay shipping both ways.

DEALER WARRANTY SERVICE ­ is to be reimbursed when we receive copy of his Service Report and defective components in the amount of $10.00 for each unit so serviced. Units requiring the same service within 90 days are the responsibility of the authorized service center.

SPEED OF SERVICE ­ All units are to be repaired before the end of the second normal business day following the date of the receiving record. (Exceptions include case damage and large modular systems.)

CUSTOMER HAND CARRY ­ Units may be repaired at the factory while the customer waits only if appointment is made with Customer Service Manager at least one day in advance.

MODIFICATION ­ All units returned for whatever reason are to be updated to the latest or final design of their respective configurations.

WARRANTY PERIOD ­ All labor and parts are free for warranty service only if warranty card was received within one year preceding date of service.

SHIPPING ­ All shipping costs on warranty service are to be paid by Moog Music, Inc. Customer is responsible for freight to factory.

RETURN TO STOCK ­ All return to stock units are to be repaired and reconditioned to new specifications. Unreasonable damage is to be charged to dealer.

ASP
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