Six Channel Control Board; Output Board; Changing Vcas; Distortion Null Adjustment - Radio Systems Millenium-A Analog Console Installation And Operation Manual

Radio Systems Millenium-A Console
connection at header J9, a defective U9 and/or U10, or a defective R91, R93, R99, R100, R101, R102, R103, or D3, will
cause this problem. If this problem is occurring in only one channel, suspect U10 (left channel) or U9 (right channel).
6.4

Six Channel Control Board

Read the Theory of Operation before troubleshooting. The Six Input Control Board utilizes a microprocessor and clue
logic. Each section is identical and isolated from all others. A suspected section can be swapped with a known good
one by interchanging ribbon cables.
6.5

Output Board

Read the Theory of Operation before troubleshooting. The Output Board provides several different functions for the
console. It is important to understand the signal path before attempting to troubleshoot. Briefly, the audio current from
the mix buses is converted back to a voltage, this voltage is fed to both the monitoring circuitry and except for the cue
bus, to the output amplifiers The output amplifiers feed the output connectors and the VU meter amplifiers. The VU
meter amplifiers feed the meters and the peak LED detectors. If a problem occurs in this chain, signal trace to the last
stage in the chain that performs properly and then troubleshoot the following stage. Replacing the IC will usually cure
the problem. As pointed out, current summing mix buses are utilized in the console. Therefore, when troubleshooting a
correctly functioning mix bus, no voltage will be measurable on the bus itself.
The monitor amplifier circuitry can be broken down into several sections for troubleshooting. The first involves the
CMOS analog select switches U18 and U20. If no audio, or audio that is different from the one selected, is available
from the unmuted monitor outputs (left and right channel), ICs U22, U18, U20, U27 or the Monitor Control Board and its
connections to the Output Board should be checked. Audio maybe monitored at pin 3 of U18 and U20. The Six Channel
Audio Board section outlines the control voltages used by U18 and U20 for signal selection. These maybe measured at
the IC.
If audio is missing from the left or right unmuted monitor output, suspect U22, or U18 (right channel), or U20 (left chan-
nel). If audio is available from the unmuted monitor output but not the muted output, suspect U23 and U24. If the only
problem is the dimmed monitor output, in both the left and right channels suspect U23, and U33. The VCA control volt-
age can be carefully measured at pin 1 of U33. With the Mute 1 bus inactive, the front panel monitor level control should
vary the voltage from +.6v to -.05v. With the Mute 1 bus active, the dimming trimmer should vary the voltage from +.6v to
-.05v. If the problem is only occurring in one channel, suspect U24 and U26 (left channel) or U25 (right channel).
The headphone amplifier circuitry is similar to the monitor amplifier circuitry described above. The major difference is
that U27 either selects the CMOS analog switch control voltages from either the headphone switches (normal mode) or
the monitor switches (follow mode).
The cue amplifier circuitry can be monitored in three places. If signal is not present at pin 1 of U12, replace U12 or
check the associated components. If signal is present at pin 1 of U12, check for signal at C114. If signal is not pres-
ent suspect Q6 or associated components. If signal is present at C114, suspect U28, U29 or the front panel cue level
control or a connection from the Headphone Control Board. The VCA control voltage at pin 2 of U29 can be carefully
measured. The voltage will vary from +.6v to -.05v depending on the setting of the level control.
6.6

Changing VCAs

6.6.1

Distortion Null Adjustment

VCA distortion null is typically not required unless a VCA or distortion trimmer has been replaced. To null distortion on
an input board:
1. Connect a +4dBv, 2kHz sine signal to the defective input. Remove any gain jumpers or attenuators.
2. Turn the mixing channel on and set the fader for "0." Select the program bus output.
3. Connect a distortion analyzer to the defective program output (right or left) and adjust the associated VCA
distortion null for a minimum distortion reading on the analyzer.
If a monitor, headphone, or cue VCA needs replacing:
1. Connect a 4dBv, 2kHz sined signal to any line level input associated with the defect (right or left). Remove
any gain jumpers or attenuators.
2a. For defective monitor or headphone VCA's, select the program bus and turn the channel on. Set the fader
to "0."
2b. Set the monitor or headphone level control to 1/2 full.
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