SECTION 4 - MAINTENANCE
4-1 General lnformation
The UItra-VU is designed to need a minimum of
maintenance for long trouble-free operation. Should
repair be necessary, the technician should first read
the information in the manualconcerning the circuits
in question and should follow proper procedures for
testing and replacing semiconductors. Logitek engi-
neers are readily available at the factory to provide
technical assistance both during and after the war-
ranty period.
* * * * * * * * * * WARNING * * * * * * * * * * *
The inside of the Ultra-VU contains no controls or
user serviceable parts. The cover should only be re-
moved by competent technical personnel capable of
servicing this type of equipment. Hazardous voltages
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4-2 Fuse
The primary winding of the power transformer is
f used with a 112 amp slow-blow 20mm f use housed in
a fuse holder in a slide-out drawer under the power
cord on the rear panel of the unit. lt should only be re-
placed with f uses of the same type and current rating.
The power cord must be unplugged from the rear
panel to gain access to the fuse holder.
* * * * * * * * * * WARNING * * * * * * * * * * *
Do NOf replace the fuse without f irst disconnect-
ing the meter's power cord from the wall socket, as
dangerous voltages are present which may cause
electrical shock. Always use f uses of the same value
and type as specified in this manual. Do NOf use
f uses of a higher value than those specrf ied, as shock
:1':':::i'l:if i': I:'.;":'l'. * * * * * * * *
A blown fuse is most often, although not always, a
symptom of another failure. Related circuitry should
always be carefully examined after any fuse failure,
especially if a replacement fuse also blows.
4-3 Handling of CMOS lntegrated Circuits
All logic components in the Ultra-VU meter are
CMOS type integrated circuits. Even though all cir-
cuits have built in static discharge protection, special
care must be taken in the handling of these devices,
particularly in dry environments.
* * * * * * * * - IMPORTANT* * * * * * * * * *
Do NOf remove or handle CMOS integrated cir-
cuits except in a grounded environment which is f ree
of the risk of static electricity. Store such circuits on
conductive foam or in anti-static controllers. Do NOf
store on styrofoam or other plastic sheets. lmproper
handling may damage these devices.
** Ultra-VU NBC896 & NBC996 Operation & Seruice Manual *r
Page B
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Access to the circuitry of the rackmount meters is
accomplished by removing the eight screws that at-
tach the top cover.
4-5 Power Supply LG-253
Each Ultra-VU contains a ground isolated and fil-
tered step-down power supply to create the neces-
sary operating voltages. This supply is located on a
PCB on the right side of the meter enclosure.
Mains AC from the power entry module J2 is fed
through f use F1 , located in a drawer under the power
cord in J2, to J1 on supply card LG-253. J1 feeds volt-
age selection switch S1 which connects the dual pri-
maries of transformer T1 in series for 230VAC
operation or parallel for 1 15VAC operation. The dual
secondaries of T1 are wired in parallel and loaded
with a full-wave bridge rectifier RT1. The DC output
of RT1 is filtered by capacitors C1 and C2 and fed to
the red and green output pads. The voltage should be
between 8 to '10 VDC with less than .5 volt of ripple.
Analog input models will also have a charge pump
conslsting of lC1 and C3 that feeds filter C4 and the
black output pads. The voltage should be -B to -10
VDC with less than .1 volt of ripple.
Jumpers soldered to the output pads feed power
to one or two meter control cards.
* * * * * * * * * * WARNING * * * * * * * * * * *
Dangerous voltages are present on the bottom of
the power supply card. Always disconnect the AC
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4-6 Dual Digital/Alarm Card LG-257a
Power from input connector P5 is connected to
voltage regulators lC3 and lC4 as well as display
board connectors P6 and P7. lC3 is a +SVDC regula-
tor that f eeds power to the analog f ront end of data re-
ceivers lC1 and lC2. The voltage is f iltered by C5- C9
and clamped against over voltage and voltage rever-
sal by D2. lC4 is a +SVDC regulator that feeds the
digital portion of lC1 and lC2 and all other circuits on
the control board. The output voltage !s filtered by
C10 and clamped by D3. Distributed powerf iltering is
supplied by C1 1-14^
On power up, the DSP is kept in reset by lC6 until
the power has stabilized, ensuring a good power on
reset. lC6 also contains a watchdog timer that will re-
set the DSP if its ST pin in not taken low at least once
every 150 mSec. This pin is normally pulsed low
every 5 mSec by the left bargraph load signal.
The DSP (lCB) is clocked by a12.2BB MHz crystal
oscillator consisting of Y1,C'15,C16 and an internal
