Infinity Intermezzo 4.1t, Service Manual

Page: 11 / 45

INTERMEZZO 4.1t
11
IM 4.1t ADJUST BIAS PROCEDURE
(Mandatory when any output MOSFET transistors Q305, 310, 320, 321, 306, 307, 311, 312 are replaced)
1. Amplifier should be unplugged and OFF.
2. Remove Amp assembly from cabinet; remove rear plastic guard, and detach entire assembly from
black plastic cup containing the controls. All wires exiting the assembly can remain connected
unless they will prevent you from removing the amplifier or accessing potentiometers on the Linear
board PCB in the following steps.
3. Identify the Linear board assembly (PCB with the output transistors).
4. Adjust RP301 and RP302 fully counterclockwise. See diagram below.
5. Apply 120 VAC power to unit; turn power switch ON.
6. Verify that LED lights on the front Gain Control dial, unless you have disconnected the plug.
7. Connect voltmeter set to DC millivolt range to twin pins on terminal J303, on Linear board.
8. Verify initial voltage is less then 0.1mV.
9. Adjust RP301 clockwise until voltmeter reads 0.3mV + the initial current from step #8.
10. Adjust RP302 clockwise until voltmeter now reads 0.6mV + the initial current from step #8.
11. Turn amplifier OFF. Disconnect AC power to unit.
12. Remove voltmeter from terminal J303.
13. Replace assembly to black plastic cup containing the controls (be sure to reattach green ground
wire to one screw); replace rear plastic guard, any wires if disconnected, and replace amplifier back
into cabinet.