CZRVER CORPORAff ION MODEL C-9 SERVICE MANUAL
§HT5
5.o IC REPLACHmFT
Subtle yet excessive levels of noise or distortion are invariably
caused by ''below-spec" ICs. Prior to replacing any IC for these reasons,
hchirever, run the noise and distortion tests below:
5.1 mstall shorting plngs in both inputs. Connect an IRE "A" veighted
f ilter at the input of an AC voltmeter. All switches should remain in
the positions described earlier (INI. Rrmlo & LIST. ANGIE are Our,
Hch"RAM is IN}. The ran noise output of either channel should
measure less than 30 microvolts. If an "A" veighting filter is not
available, the noise may be measured "flat". A good rule of thumb in
the case of the ICs used in the C-9 is to expect about three tines the
noise reading betveen an ''A" veighted measurenent and a "flat" one.
Any reading below 100 microvolts { flat} is considered acceptable.
5.2 If output noise exceeds the specification, probe the outputs of each
successive stage's IC§ until the offending chip{s) are located and
replace them.
5.3 Distortion is to be measured at the "rated" output of 2V rms. All the
front panel pushbuttons are to be engaged {in} and the bandwidth of
the distortion analyser should be limited by use of an 80kHz filter to
suppress RFI since the cover is rermc]ued. Under these conditions, the
TID readings should fall below 0.05% for any frequency betneen 20Hz
and 20kHz.
5.4 If HH) exceeds the specification, probe the outputs of each successive
stage's ICs until the offending chip{s) are located and replace than.
5.5 It is our experience that if noise and 'HH) specifications are net, the
IM distortion will almays fall below the specified level. If you wish
to measure it, be sure to use the standard SMPRE frequency mix and
signal ratios. The resulting lrEasurement should be below .05% at the
rated {2 Volt) output.
5.6 If cecillation {self-sustained ringing) is the problen,locate the
earliest IC output node in the circuitry at which it is present and
replace the offending part.
6. o FunrerloEL vmlFlcAIION
Cmce the basic circuitry is functioning without obvious problems,
tests may be ccxpleted to determine the critical aligrment of the primary
Holographic circuits. Since these circuits purposely cross-feed portions
of the stereo signal, expect a considerable amount of "crosstalkft between
channels. This is normal and irell controlled. Begin with all pushbuttons
in their Our positions.
6.i Drive both inputs with a lkHz signal at OdEm {.775 Vrms) and verify
the presence of identical signals at each output. Switch the mmceRAM
funetion to its on (IN) position.
6.2 Using a dual-trace oscillosccpe, connect one probe to IC2, pin 4 and
set the scope's triggering to activate and lcok en that signal.
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