www.bmc-audio.com

Balanced Music Concept

Required Items / Tools

Ÿ 2 x Ampere-meter, fused up to 10A.

Ÿ 1 x Volt-meter.

Ÿ 2 x Test cable with dummy-fuse, PTC fuse, Ampere-meter and

banana plugs.

Ÿ Adjustable AC power transformer such as a Variac or other similar

unit. For safety a galvanic isolation is highly recommended.

Ÿ 1 x long nose pliers, isolated handle.

For Opening:

Ÿ T15 TORX screwdriver or ratchet.

Ÿ 5mm hex head ratchet or screwdriver.

Opening the Amplifier

Ÿ Turn the amplifier upside down.

Ÿ Remove the 4 hex head screws first

Ÿ Remove the various TORX T15 screws.

Ÿ Don’t open the lid at once!!! Slowly lift the lid from the rear panel

side, reach for the fan cables with one hand and unplug them. Now

the lid can be removed.

VoltmeterAmperemeter Amperemeter

Test Cable

GND point for voltmeter

CS2, M2, C1, S1 Standard Test Procedure

Speaker Output Inverted

+5V Supply

-29V Supply

-31V Supply Speaker Output

+31V Supply

Testpoints

Speaker Output +29V Supply

Before Starting:

Ÿ Identify the locations of all the test-points on both channels.

Ÿ Connect and set the ampere-meters to 10A DC

Ÿ Connect and set the volt-meter to a range covering up to 50V, or auto-

range. Clamp the black wire to a GND test-point.

Ÿ Make sure the variable transformer is set to 0V.

Ÿ Never switch on the amp

with full AC voltage while

testing cables and ampere-

meters are connected. The

inrush current might break

the meter’s fuse.

Ÿ Remove the 2 power fuses

and plug the test cables

into the fuse holders. Now

the power is connected via

the ampere-meters.

When it is not clear whether the amplifier is damaged or not a safe startup

procedure should be used; such a procedure will reduce the possibility of

additional damage and make it easier to locate the problem.

Ÿ Make a visual inspection for foreign matter or loose connectors.

Ÿ Turn on the amplifier’s power switch with the adjustable power supply

set to 0V.

Ÿ Carefully increase the AC voltage to about 1/5 of the nominal AC

voltage. The ampere meters will show some current during this

process, but should revert to a very small current reading.

Ÿ Check the supply voltages for symmetry and validity. The supply

voltages at this stage will be just a fraction of the target value, but a

missing voltage already can be detected. E.g. +31V and -31V should

have about the same value with reversed polarity, the 31V supplies

should be higher than the 29V supplies... Ignore the 5V and the +-15V

voltages at this stage.

Ÿ Check the speaker DC offset output voltage (4 test points). All voltages

should be about the same.

Ÿ Now raise the AC power voltage to about half of the nominal voltage.

Ÿ Do the voltage and speaker output check again. Include the 5V and the

+-15V voltages. The target voltages are not reached at this stage. Refer

frequently to the ampere meter!

Ÿ If these measurements are consistent, increase the AC voltage to the

nominal voltage value and prepare for a fast power off in case of a problem.

Ÿ After the countdown reaches “5" the power current sources will be

activated. This is the most critical stage.

Ÿ The ampere meters should now show between 1.1 and 1.3A.. In case of

a significantly higher value turn off the amplifier.

Ÿ Check all voltages again; normal operating values should be shown.

Ÿ Check the speaker output DC offset again; now about -1 to -1.2V

should be measured against GND. The differential voltage at the

speaker output should be below 50mV.

In case you need B.M.C.’s support for fixing a problem an as detailed as

possible report is required:

Ÿ Describe the problem reported by the customer.

Ÿ Report exactly the stage of testing at which the unit failed.

Ÿ Report exactly which test-point showed a deviation of the normal.

Ÿ Describe any deviation of your test setup from that suggested in these

instructions.

Safe Startup Test Reports for Support