Current Sensor Zero Calibration Check; Main And Mosfet Power Supplies Main Plug - In Board Rails; Bias Check; Output Dc Offsets - Classe Audio Delta Series Service Manual

Main plug-in board rails
Measure the voltages on the accessible ends of R140 and R141 on each of the main boards. The values of
R140 and R141 on one main board should be exactly the same. With the main supplies at +/-66.0Vdc, you
should see a value between +/-53.4Vdc and +/-54.6Vdc (relative to analog ground on the backplate) for
CA2100 and CAP2100. (relative to any ground on Aux. Power Supply. See appendix H for full specifications.

Bias check

Measure the bias voltage on resistor R116 (or Q1) on the left ("inverted") 5-device heatsink (relative to the left
output), and on R111 (or Q 11) on the right ("non-inverted") 5-device heatsink (relative to the right output).
Exactly 12 minutes after first power-up (from completely cold) the bias should have risen to within 1.0 mV of
the target value (as indicated on the heatsink burn-in sheet). Note that the target value for a Left heatsink is
labeled "next Q1 trim", whereas the target value for a Right heatsink is labeled "next Q11 trim" (because this
heatsink is negative-side-up).
If the bias is NOT within 1mV of the target at the 12-minute mark, then turn trimpot RV101 clockwise to trim it
up to 1mV under the target value. Make a note of this on the back of the "traveler" sheet (under the checklist)
with your initials.
For a final BIAS check, set your voltage to 66.0 Vdc. Leave your unit ON for about 1 to 3 hours. After this
time check and adjust your BIAS perfectly. Then start the Final test procedure.

Output DC offsets

Measure the DC offset voltages on the output posts (still relative to the same ground).
They should NOT exceed +/-10mVdc.
On the CAP2100 unit, measure the DC offsets on the speaker terminals as above with the volume set to zero.
They should NOT exceed +/-10mVdc. You will also need to check the DC offsets on the main (line) and tape
outputs. The tape output is not affected by the volume setting. Make sure it is under +/-4mVdc. The main
(line) output must be checked at volume 86.0 and give +/-4mVdc <- (enter this value on the start-up
sheet)

Soft-start and bias relays check

Make sure that the big 50W soft-start resistor is 10 ohms. Monitor the AC voltage across this resistor (be
careful – both sides can be at 120Vac) as you start up the unit. During the start-up you should see a lot of AC
flowing through this resistor (current spikes as the relays click on). 8 seconds into the start-up sequence this
soft-start resistor is shorted out and you should see only a couple of mVac (around 6 to 9mVac).
Observe the bias as you power on the amplifier (from Standby). It should be zero until about 7.5 seconds after
the start of the power-on sequence. Verify this on all the heatsinks. In other words, make sure that all the
biases are zero in the first 7.5 seconds after you power-up the unit.

Signal and mute check

Connect an input test signal from your function generator and observe the output of the unit on the
oscilloscope as soon as you power it up. Verify that the signal passes (check both balanced and single-ended
inputs on ALL channels. On CAP2100, just check Balanced and Line 1 input only with volume set to 86dB, all
of the inputs are tested upstairs). Make sure that the phase of the output is exactly the same as the phase of
CA(P)2100 AMP Service Manual v1.4 inc voltage change info .doc Page 26 of 50