Crown D-150 - Circuitry Details; Principles of Operation; Test Procedures

5.5.. TEST.EQUIPMENT .
The D-150 amplifier is a relatively’ conipiex unit, and con
sequently requires a comprehensive array of standard and special
test equipment for complete servicing. Arecommended listof test
equipment i T: 5
“GROWN
in the absence of 2 complete set of test equipment, it should be
noted that most troubleshooting can be successfully done with an
oscilloscope, an ohmmeater, a voltmeter and a signal generator.
Any: arnplifier..calfunctions...which.cannot -be-.identified..and
repaired with this basic equipment should be referred to the
CROWN factory or authorized service center.
55.1.
Calibration
of
Test
Equipment
-
"FE
iniportatt
{Hat
test
measuréiients
made
during
servicing
be
accurate and- dependable: Othenwise the performance ‘of the,
ly.
manth- intervals) checks. f tess: expensive fend ‘hereby less de-
spendable): test equipment is «ised, trequent-calibration is nec-
measurements when dealing wih high-purity arnpitiers such as
the CROWN 0-150.
the power supply has: beeri wi :
line Voltage should be measured with a peak reading ac volt-
melér.and-adjusted to. the rms equivalent voltage (to. com
spensate for. Nine-voltage regulation errors: during-the course of
when the amplifier ig wired for OV (IHF Standards). Wthe
amplifier is wired for 240V; the equivalent test may be given
by applying 240 volts: <-
2. The loads should be resistive, having tess than 10% reactive
“eables through Which the load
should employ only hdhcrent canes an Be con
Pe unding-pos re
Ps SHOUIE be Set 16 Maximum forall dis-
Never connect the oe ofthe cable bai ce
to the Inpetproands-
20
Ground. toops are, especially obnoxious. when.measuring dis-
tortion. An 1M distortion analyzer, forexample, has its input
and output terrninais tied to a common ground. Such a test
should use an ungrounded output return, with the output
jead(6) wrapped around the well-shielddd and grounded input
cable.
6. Always monitor the test oscillator wher measuring Wequency
response: Use a wide-band ac voltmeter: or use the same
meter for both input and output level measurements, if the
meter’s frequency response is known not te be dependent on
attenuator Lien
critical. For example, a 2% voltage error together with a 1%
fesistatice errorcan result in an erorat LO.watts power inten
8-ohm load.
8 Residual distortion and noise levels should be fully known for
2h Se oer a
amplifier performance.
3 hess teas maces SIRS Ha ae
the-terviinats: A convenient current is one ampere as the
resultant voltage will read directly inohms for (25): Damping
factor is defined-as Z/lghi where a) is typically @ohins.A.
convenient generator for the 1A current ig that arnplifier
provide TAwhen 8 volts are eases =e
that charinel net.under: test). ..
10.. Never measure hurrvand noise when in thepresence of strong
magnetic fields. “The. amplifier should be at least 4 inches
away from any large metallic objects or shield. plates for a
reading to be meaningful.
Ll. Noise measurements should be taken with a bandpass fitter
of 20-20. KHZ. For audio purposes the measurement of noise
above 20 KHz is unimportant.
12. When repairing an araptifier it should not normally be oper-
ated:withe: toad - until tpertorms properly unloaded. Htserious
problems with the amplifier exist, a i nly. compound
those problems by blowing fuses causing additional
damage by drawing high current. ae ees
13. Obmmeter tests can usually be performed on-semiconduc-
Aallin the 5-25.ohm.range.: sR
fesistor values without removing them: ‘from the circuit
and without forward biasing any junctions, the ein robe
100 mweange? should be used. «
The affect of par. ilar is ie be Rasta de.
termining: whether a test reading is: normal, The. simplest pro-
cedure-is-2-comparison with the. same-reading under identical