Model 686C Section IV
Paragraphs 4-1 to 4-2
SECTION IV
MAINTENANCE
4-1. GENERAL. B. MAGNET POWER SUPPLY CAUTION
This section contains information on the maintenance The magnet power supply is isolated from the
and repair of the sweep oscillator. A suggested "quick chassis and the rest of the instrument. This supply
check"procedure is given for verifying that an instru- is a voltage doubler circuit which is directly con-
ment is operating properly. These checks are made nected to the power line. All filter capacitor cans
with the cabinet in place and will verify instrument and/or terminals in the magnet power supply are thus
performance for routine maintenance or incoming part of the ac power system. Accidental shorts from
quality control checks. The operator can also use this parts of the circuit which are connected to the un-
procedure to check that his instrument is operating grounded side of the power line to the grounded instru-
normally and is within specifications. ment chassis will severely damage the parts before
the fuses can blow. Care has been taken in design
A troubleshooting chart is given which systematically layout to minimize exposed parts which are connected
leads the technician through the instrument and also to the ungrounded conductor (black power cord lead).
indicates which adjustments must be rechecked after
repairing any particular circuit. Silicon Rectifiers are used in the magnet supply. Be-
cause of the very low forward resistance characteristic
of these units, they will be instantly destroyed if
A test procedure is included which covers adjustment accidently short-circuited. Be careful when making
of all circuits for optimum performance. Specifica- voltage measurements not to let the probe slip and
tions for the 686C Sweep Oscillator are given in the short-circuit the voltage doubler circuit.
front of this manual. The test procedures in this
manual give additional tests and data for your con- Voltage measurements in this supply, other than
venience in analyzing a particular instrument. These ripple measurements, should be made with an insulated
extra checks and the data they contain, are not to be case voltmeter. Electronic voltmeters such as the
considered as specifications. @ Model 410B and 400D have the ground terminal
connected to the instrument chassis and cabinet which
is in turn grounded by the green grounding wire in the
Standard, readily available components are used for power cable. Accidentally connecting the meter input
manufacture of @ instruments whenever possible. ground conductor to the ungrounded power conductor
Your most convenient source for spare or replace- will short out the power source through the NEMA
ment parts is your local @ Sales Representative who ground on the voltmeter chassis. Low level ac ripple
maintains a parts stock for your convenience. measurements must be made with caution. Paragraph
4-7 tells how they can be made.
When ordering parts, please specify instrument model
and serial number plus the component description and C. RF OUTPUT CAUTION
stock number appearing in the Table of Replaceable Never disassemble the rf cable andconnector. The
Parts (section V). bwotube rf output cable and connector are replaced as
a unit. Assembling the cable and connector is difficult,
Your local @ Sales Representative also maintains and improper assembly may cause a high swr. In addi-
complete facilities and specially trained personnel to tion, the rf output coaxial cable is directly connected
assist you with any engineering, application, test or to the bwo tube helix and can have up to 2500 volts dc
repair problems you may have with @ instruments. on it. A capacitor between the cable center conductor
and the center pin of the X-Band cover flange protects
personnel from the high dc voltage.
4-2. GENERAL PRECAUTIONS. D. NEONLAMPS
A. HIGH VOLTAGE. Neon voltage dividers used as coupling elements
WARNING: Operating potentials as high as 3200 in dc coupled circuits are aged, polarized, and selected
volts are present at certain points in the instrument. for correct voltage drop. Refer to paragraph 4-18 for
details before replacing any of these lamps.
The power supplies are all regulated and are capable
of delivering relatively high currents for short periods. E. OSCILLOSCOPE
Be alert at all times to danger points. Do not remove
the red safety cover which covers most of the high With application of a positive external signal at the
potential circuits unless absolutely necessary. Re- horizontal input of an oscilloscope, some oscilloscopes
member that the instrument chassis is always grounded sweep from right to left, others from left to right.
by the green grounding wire and NEMA 3-prong con- The illustrations in this manual show the oscilloscope
nector; do not defeat its purpose with a three-prong horizontalsweeps going from right to left. Thus when
to two-prong adapter or by removing the ground pin. using an oscilloscope that sweeps from left to right
00034- 1 4- 1 |
ACEC
