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The SMR™821a offers optional features for specific applications. These options include transformers
for the microphone inputs and the ability to defeat the functionality of the Channel 7/8 select switch.
These options and modifications require access to the inside of the SMR™821a. It highly
recommended that the installation of the optional microphone transformers and modification of the
Channel 7/8 Select switch be performed by qualified service personnel. There are dangerous voltages
present inside the unit as well as static sensitive components. Damage to the SMR™821a internal
circuitry caused by an unqualified persons is not covered under warranty‚ and in fact‚ could void the
warranty altogether.
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Optional transformers for use with the microphone input circuits are available from Peavey Electronics
Corp. (part # 70500852). The optional transformers may be added one at a time‚ all at once‚ or in any
combination. To ensure that the transformers are properly installed‚ please refer to the instructions
and illustrations in this section. If you have any questions or are not sure about the correct procedure‚
do not hesitate to call our Tech Support Group.
Refer to Figure 14‚ “Cutaway of circuit board showing jumper locations for installation of optional
microphone transformers” while performing the following steps:
1. Unplug the SMR™821a from the AC voltage source.
2. Remove the 6 screws securing the top panel. Remove the top and set aside.
3. Remove the 5 screws securing the rear panel to the chassis.
4. Remove the 5 screws securing the front panel to the chassis.
5. Carefully turn the unit upside down.
6. Remove the 11 screws securing the circuit board assembly to the chassis.
7. Carefully turn the entire unit right side up. One end of the circuit board assembly (with the front
and rear panels still attached) can be lifted out of the chassis with power supply wires still intact
to access the bottom side of the circuit board.
8. Locate the 6 round transformer outlines.
9. Before installing the transformers‚ you will need to cut some jumpers and resistors. These
components are labeled with reference designators on the board.
10. For each transformer installed‚ 3 jumpers and 1 resistor will need to be cut. The following table
shows which components need to be cut for their corresponding transformer.
Transformer T101 T1201 T301 T401 T501 T601
Components J102 J103 J202 J203 J302 J303 J402 J403 J502 J503 J602 J603
to be cut J105 R116 J205 R216 J305 R316 J405 R416 J505 R516 J605 R616
11. The transformers can only be inserted into the board one way. Place a transformer into the
circuit board and solder in place.
Repeat process for each transformer being installed.
Re-installing the Circuit Board and Re-assembling the Unit
1. Place the circuit board assembly (with the front and rear panels still attached) into the chassis.
2. Carefully turn the unit upside down and replace the 11 screws securing the circuit board
assembly to the chassis.
3. Carefully turn the unit right side up.
4. Replace the 5 screws securing the front panel to the chassis.
5. Replace the 5 screws securing the rear panel to the chassis.
6. Place the top panel on the chassis and replace the 6 screws securing it to the chassis.