Classe Audio DR-8, Service Manual

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PRO-SVR_LEGACY Page 5 of 11
Start Up Procedure
When receiving a unit, an assiduous visual inspection must be performed. Do not connect the unit without
analysing the symptoms reported by the customer and the results of the inspection.
Using the troubleshooting guide, find the problem and proceed to the repair. Once this step is done, follow
these steps, known as the start-up procedure, to ensure that everything in the unit is in working condition.
1. Proceed with a post repair visual inspection. Take the time to check if every wire is reconnected
properly, every screw is bolted on, no soldering and/or metal residues lying in the unit, every fuse has
been replaced, etc.
2. Connect the unit to a variable transformer, setted to 0Vac.
3. Turn the bias trimpot (R16) counter clockwise until a click is heard.
4. Slowly raise the voltage to 10Vac, and check positive and negative rails and pre-driver supply. Check
fuses.
5. If one or more supply are not within specifications, return to the troubleshooting guide.
6. Slowly raise voltage until you hear relays click, this point is around 55Vac. Recheck every supply.
7. If one or more supply are not within specifications, return to the troubleshooting guide.
8. Raise voltage to 120Vac. Recheck every supply
9. Report to Calibration and adjusments to adjust bias and DC offset. Note that bias can be adjusted to
14mV, and the following tests can be performed before the unit is send to the burn-in bench for a 24
hours warm-up.
10. Connect the unit to a load, and to a source using balanced inputs and single ended inputs,
independently.
11. Perform a test with a 200Hz, a 2kHz and a 20kHz tone, both sinus wave and square wave. Check the
output with a oscilloscope, on 4 ohms and 8 ohms loads. Take special cares about oscillation and phase
correlation between channels.
12. Connect the unit to a small speaker, and short the input. Check for any noise. Perform this step with
single ended inputs and balanced inputs, independently.
13. Put the unit on a burn-in bench, and let it sit for 24 hours, then readjust bias. Let the unit on the burn-
in bench for another 72 hours.
14. Redo steps 10 to 13 before shipping to the customer.