S E R V I C E I N S T R U C T I O N S ( C o n t ’ d )
push-on retainers so that it may be raised above the chassis for service without complete removal. With all power turned off, depress retainer locking tab, if any, and pry each corner of the board from its retainers. Lift the board straight up assuring that all wires clear any obstructions, and position the two lower board mount- ing holes over the two upper plastic retainers. Snap the board over the retainers, thus exposing the component side and most of the conductor side of the board. After positioning one or more boards in this manner, the SE30 may be operated and measurements made.
3. All connections to printed circuit boards are made by push-on terminals crimped to color-coded wires. To remove a printed circuit board, first turn off all power and remove ac line cord, then grasp each brass ter- minal with long-nose pliers and pull away from board. The board may then be pried from its retainers and lifted out of the chassis.
4. Figure 6 illustrates the location and position of each printed circuit board component. Note that all such components have three-digit reference numbers, the first digit of which denotes the printed circuit board number. The colors of wires connected to each ter- minal are also shown to aid in reconnecting boards. Color abbreviations with asterisks refer to stranded No. 20 AWG wiring, and those in parenthesis refer to integral component leads. All other wires are smaller, stranded No. 24 AWG.
5.Printed Circuit Board 4 requires special handling, as noted in Figure 6B. To avoid possible erratic operation under high humidity conditions, the area of the board which includes Q401, R401-404, and C401-403 must be kept free of contamination from perspiration, skin oils, and the like on both sides. This area should not be touched with the fingers, and if any of these com- ponents must be replaced, soldering flux must be re- moved by brushing with a solvent such as clean wood alcohol (methanol) or denatured alcohol. (Do not use rubbing alcohol.) After flux removal, rinse with dis- tilled water to remove electrolyte contaminants. CAUTION: Alcohol is flammable. Do not use near fire.
Note that FET Q401 is mounted inverted to the board with a direct soldered connection between R402 and
the gate lead.
6. Integrated circuits MC201 and MC301 are mounted in 14-pin sockets to facilitate removal and replacement. The notch on one end and a dot or mark identify pin 1, which must be positioned as shown in Figures 6A and 6B and as indicated on the printed circuit board.
7.Typical voltage measurements are given for Various points in the circuitry in Tables 2A, 2B, and 2C. The notes to Schematic Diagram and Test Voltages Outline the test conditions for these measurements. Voltages at all printed circuit board terminals are given in Table 2A, and board-mounted transistor and integrated cir- cuit terminals voltages are given in Tables 2B and 2C.
All voltages are measured with respect to chassis ground.
8. Replacement of Printed Circuit Boards 2, 4, or 5, or of MC201 will necessitate recalibration of the com- pression system as outlined below. In addition, Printed Circuit Board 3 replacement requires Gated Memory recalibration, and Printed Circuit Board 5, or meter Ml replacement require VU Meter calibration. Com- pression system calibration should also be checked if meter M1 is replaced.
CALIBRATION
Each SE30 Gated Compressor/Mixer is individually cali- brated at the factory with six internal trimming potentiom- eters and a selected fixed resistor, to compensate for individual component variations and to assure uniform and accurate performance. The complete calibration procedure is given here for qualified service personnel with access to laboratory quality instruments, in the event that com- ponent replacement or changes in internal control settings necessitate recalibration.
For those without adequate facilities, the complete unit may be returned to the factory for calibration. Carefully repack the unit and return it to the factory Service Depart- ment. The unit will be returned to you prepaid.
EQUIPMENT NEEDED:
Ahigh-impedance (2 megohm or greater), high-sensi- tivity (10 mV full scale or better) ac voltmeter, such as a Hewlett-Packard 400 GL or Ballantine 861, is necessary for accurate results. The meter should be equipped with a clip-on shielded test cable.
In addition, a sine-wave audio generator, capable of producing 1 volt at 1 kHz with less than 1% total harmonic distortion, is desirable. A generator with an accurate 10 dB stepped output attenuator, such as the Hewlett-Packard 204D, will greatly simplify changes in input level necessary during the procedure. A shielded cable to connect the out- put of the generator to the professional three-pin female Input 1 receptacle will be needed. Unbalance the generator output (low side connected to chassis), if generator output is balanced, and wire the cable so that input connector pins 1 and 3 are to the low side of the generator and pin 2 is to the high side.
There are three different portions of circuitry which re- quire calibration: the Gated Memory, the compression sys- tem, and the VU meter. A standard blade screwdriver may be used to adjust the trimmer potentiometers during the Gated Memory and compression system calibration. VU meter calibration requires the selection of a fixed resistor and soldering it in place on P.C. Board 5.
During the Gated Memory and compression system Cali- bration, the internal signal level at terminal A of P.C. Board 3 is monitored and adjusted. The signal voltage at this point will be referred to as E3A. The test signal is provided by an external sine-wave generator, or the internal Tone Oscillator may be used. If an external generator is used, connect its mating cable to the Input 1 connector (13A) with the Input switch (14A) set to LINE, and the Input 1 Filter switch (2A) set to IN. Adjust the generator for 1 volt output at 1 kHz. If the Tone Oscillator is used, set the front-panel Input 1 Filter switch (2A) to TONE OSC.
If the Tone Oscillator or an external generator without a stepped attenuator is used, the voltage at terminal A of P.C. Board 3 (E3A) should be adjusted to the required values by the Input 1 control (1A). If the external generator does have a stepped attenuator, the Input 1 control (1A) should be adjusted so that a l-volt generator output results in 1 volt at terminal A of P.C. Board 3. Lower levels are then obtained by using the generator’s attenuator.
Calibration must be performed with the top cover re- moved to permit access to the trimmer potentiometers and test points, and during compression system calibration, removal of the bottom cover is also suggested. For com- plete safety from hazardous powerline voltages, the SE30 should be battery-operated during calibration, using fresh batteries which indicate +1½ VU or better on the meter, with the Batt. Check switch (9) actuated and the Power switch (11) ON.
