SHR-04 CHANNEL BOARDThe SHR-04 Channel Boards are assembled and installed inpairs. Therefore, SHR-04s for Channel 1 and Channel 2 constituteone pair, those for Channel 3 and Channel 4 constitute anotherpair, etc. To remove any pair of Channel Boards:1. Remove the control knobs by pulling them off the shafts.2. Remove the two flat-head Phillips screws that hold the ChannelBoard Assembly in place. One screw is attached to the top ofthe front panel ledge, the other to the chassis bottom.3. Disconnect the Channel Bus Connector from the top of eachof the two Channel Boards.4. Disconnect the 3-pin connector (coming from SHR-01 InputBoard) from the bottom of each of the two SHR-04 ChannelBoards.5. Pull the Channel Board Assembly horizontally backward tofree the control shafts from the front panel; the Assembly isnow free of the <strong>1200</strong>.FRONT MOUNTING PANELThe Front Mounting Panel must be freed from the Front Panelin order to work on or remove SHR-05 MASTER CONTROLBOARD, SHR-06 HEADPHONES INPUT BOARD, SHR-07HEADPHONES CONTROL BOARD, SHR-09 LIMITER BOARD,SHR-08 INDICATORS BOARD and the Power On/Off Switchfrom the <strong>1200</strong>. To remove the Mounting Panel:1.2.3.4.5.6.7.8.9.Remove the two flat-head Phillips screws from the frontpanel ledge above the Mounting Panel.Rest the <strong>1200</strong> on its side with the fan and mounting panelupwards.Remove the top three Phillips screws holding the front panelto the chassis bottom. Leave the bottom screw (below Channel1) in place. (This will permit swiveling the front panel farenough away from the chassis to allow the Mounting Panelto be freed from the <strong>1200</strong> after other required disconnectionshave been made.)Remove the knobs from the control shafts of the Master andHeadphones Controls.Disconnect the 3-pin connector from P701 on the HEAD-PHONES CONTROL BOARD.Disconnect the 3-pin connector from P601 on the HEAD-PHONES OUTPUT BOARD.Disconnect the CHANNEL BUS connector from P501 at thetop of the MASTER CONTROL BOARD and disconnect 8-,4-, and 5-pin connectors from P502, P503, and P504 at thebottom of the MASTER CONTROL BOARD.IMPORTANT: Mark all connectors before removing them sothat they can be reconnected correctly.Loosen the cable tie that holds the cable harness to the holein the outside bottom of SHR-05.Swivel the front panel away from the chassis bottom enoughto permit pulling the control shafts out of the front panel andpartially freeing the Mounting Panel from the <strong>1200</strong>. (Thepanel is still connected to the <strong>1200</strong> by the transformer leadsconnected to the On/Off switch.) From this position it ispossible to remove or work on boards SHR-05, -06, -07,-08, and -09.SHR-05 MASTER CONTROL BOARDTo remove SHR-05 MASTER CONTROL BOARD from theMounting Panel:1. Remove the control knobs.2. Use a nutdriver or wrench to remove the nuts holding thecontrol shafts to the Mounting Panel.3. To free the board, pull the shafts back out of the panel.SHR-09 LIMITER BOARDTo free SHR-09 LIMITER BOARD from the Mounting Panel,remove from the front of the panel the two Phillips screws thatattach the Limiter Switch to the panel. This frees the board fromthe panel.SHR-06 HEADPHONES OUTPUT BOARD AND SHR-07 HEAD-PHONES CONTROL BOARDSHR-06 and SHR-07 are connected together by a solderedin-place4-conductor ribbon cable. If it is not necessary toreplace the cable, either remove both boards (if desired to freeone of them completely from the <strong>1200</strong>), or only remove one (iffreeing the assembly from the <strong>1200</strong> is not essential).To remove SHR-07 HEADPHONES CONTROL BOARD, removethe 7/16-inch nut that holds the control shaft to the MountingPanel. This permits the board to be freed from the panel (althoughit is still connected via the ribbon cable to SHR-06 HEADPHONESOUTPUT BOARD).To remove SHR-06 HEADPHONES OUTPUT BOARD, removethe 1/2-inch nut that holds the phone jack to the MountingPanel. This permits the board to be freed from the Panel.SHR-08 INDICATORS BOARDRemove the two Phillips screws holding SHR-08 to the backof the Mounting Panel. Pull the board back from the panel toremove the LEDs from their holes and to free the board.S2 ON/OFF SWITCHTo remove the On/Off Switch from the Mounting Panel:1. Pull the switch button off the switch control shaft.2. Remove the two Phillips screws that hold the switch to thepanel.3. Unsolder the red and black transformer leads from the switch.A<strong>1200</strong>MX INPUT EXPANSION MODULEThe A<strong>1200</strong>MX is an optional input expansion module kit thatprovides two additional input channels to the <strong>1200</strong>. A maximumof two A<strong>1200</strong>MXs can be added to the <strong>1200</strong> for a total of 10inputs. The A<strong>1200</strong>MX consists of an input connector module(SHR-15 and SHR-16), an input transformer module (SHR-17),a channel control module (two SHR-04s), control knobs, andhardware.The A<strong>1200</strong>MX circuitry is identical to the input circuitry of theother six input channels. Servicing can be accomplished in thesame manner. Printed wiring board drawings are provided withthe service drawings.CHECKING ACTIVE COMPONENTSIntegrated circuits can be checked without removing themfrom their circuit board. Measure the input, output and powersupply voltages as shown on the applicable circuit diagram.Defective transistors and diodes can be located by use of astandard ohmmeter such as a Simpson 260. Polarity of theohmmeter must be verified before these checks are made; allresistance measurements are made with the power off in thecircuit under test.With a known diode orientation, measure the diode resistancein the forward and reverse directions. The lowest meter readingwill establish the probe at the cathode end (schematic symbolarrow points to cathode) as the “minus” probe while the otherprobe will be “plus.” (Some ohmmeters are not polarized in thismanner with relation to “volts plus probe” and “volts minusprobe.“) With the ohmmeter “plus” probe on the anode end of adiode, and the “minus” probe on the cathode end, the ohmmetershould be read approximately 2000 ohms or less. With themeter probes reversed, a reading of about 10,000 ohms ormore should be obtained. If either of these conditions is notmet, one lead should be unsoldered from the circuit and the testrepeated. If the results are identical, the diode should be replaced.8
To check LEDs, connect the cathode (notch or flat on flange,tab on lead or short lead) of the LED to the negative terminal of astandard 9 V transistor battery. Connect the positive batteryterminal through a 4.7 k resistor to the LED anode. Replace anyLED that does not light.CAUTIONDo not check LEDs with an ohmmeter. The LEDs may bedamaged or erroneous readings may be obtained.To check transistors, the ohmmeter should be set to the 100-or 1,000-ohm scale. Transistors must be removed from thecircuit before testing. If all conditions in the following table aremet, the transistor may be considered free of any major defect;if any of the following conditions are not met, the transistorshould be replaced. See Figure 3 for active component leadcodes.OHMMETER CONNECTlON OHMMETER READINGNPNPNP“Plus” Lead “Minus” Lead Transistor TransistorCollector Emitter High HighEmitter Collector High HighCollector Base High LowEmitter Base High LowBase Collector Low HighBase Emitter Low HighFERRITE BEADSAll low-impedance microphone connectors contain ferritebeads (L101-L112, SHR-01). Be sure to replace any ferritebeads removed during servicing.SERVICE ILLUSTRATIONSImmediately following the parts list on the pages that followare printed wiring board foil and legend drawings, and circuitdiagrams. Once a board has been located through the partslocation photo (Figure 1), the components on that board can belocated from the board drawing. The function of the part isshown on the relevant circuit diagram.OPTIONAL ACCESSORIESThe following optional accessories are designed for use withthe <strong>Shure</strong> <strong>1200</strong> AUDIOMASTER <strong>Powermixer</strong>.Carrying Case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A<strong>1200</strong>CInput Expansion Module (2 channels,2 each HI Z and LO Z inputs . . . . . . . . . . . . . . . . A<strong>1200</strong>MX*Speaker Cable, 15 m (50 ft), with phone plugs . . . . . . A50SC240 V Conversion Kit . . . . . . . . . . . . . . . . . . . . . . . . . RKC209*Line Matching Transformer (LO Z to HI Z) . . . . . . . . . . . A95UFPhono Preamplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . M64A*For installation by qualified service personnel only.9
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