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KV-25FS12 / 25FS12C
S FETY CHECK-OUT
After correcting the original service problem, perform the following
safety checks before releasing the set to the c stomer:
1. Check the area of yo r repair for nsoldered or poorly soldered
connections. Check the entire board s rface for solder splashes and
bridges.
2. Check the interboard wiring to ens re that no wires are “pinched” or
to ching high-wattage resistors.
3. Check that all control knobs, shields, covers, gro nd straps, and
mo nting hardware have been replaced. Be absol tely certain that
yo have replaced all the ins lators.
4. Look for na thorized replacement parts, partic larly transistors,
that were installed d ring a previo s repair. Point them o t to the
c stomer and recommend their replacement.
5. Look for parts which, tho gh f nctioning, show obvio s signs of
deterioration. Point them o t to the c stomer and recommend their
replacement.
6. Check the line cords for cracks and abrasion. Recommend the
replacement of any s ch line cord to the c stomer.
7. Check the B+ and HV to see if they are specifi ed val es. Make s re
yo r instr ments are acc rate; be s spicio s of yo r HV meter if sets
always have low HV.
8. Check the antenna terminals, metal trim, “metallized” knobs, screws,
and all other exposed metal parts for AC leakage. Check leakage
as described below.
Leakage Test
The AC leakage from any exposed metal part to earth gro nd and from
all exposed metal parts to any exposed metal part having a ret rn to
chassis, m st not exceed 0.5 mA (500 microamperes). Leakage c rrent
can be meas red by any one of three methods.
1. A commercial leakage tester, s ch as the Simpson 229 or
RCA WT-540A. Follow the man fact rers’ instr ctions to se these
instr ctions.
2. A battery-operated AC milliampmeter. The Data Precision 245 digital
m ltimeter is s itable for this job.
3. Meas ring the voltage drop across a resistor by means of a VOM
or battery-operated AC voltmeter. The “limit” indication is 0.75 V,
so analog meters m st have an acc rate low voltage scale. The
Simpson’s 250 and Sanwa SH-63TRD are examples of passive VOMs
that are s itable. Nearly all battery-operated digital m ltimeters that
have a 2 VAC range are s itable (see Fig re A).
How to Find a Good Earth Ground
A cold-water pipe is a g aranteed earth gro nd; the cover-plate retaining
screw on most AC o tlet boxes is also at earth gro nd. If the retaining
screw is to be sed as yo r earth gro nd, verify that it is at gro nd
by meas ring the resistance between it and a cold-water pipe with an
ohmmeter. The reading sho ld be zero ohms.
If a cold-water pipe is not accessible, connect a 60- to 100-watt tro ble-
light (not a neon lamp) between the hot side of the receptacle and the
retaining screw. Try both slots, if necessary, to locate the hot side on the
line; the lamp sho ld light at normal brilliance if the screw is at gro nd
To Exposed Metal
Parts on Set
0.15 F 1.5 K ΩAC
Voltmeter
(0.75 V)
Earth Gro nd
Tro ble Light
AC O tlet Box Ohmmeter
Cold-water Pipe
Fig re A. Using an AC voltmeter to check AC leakage. Fig re B. Checking for earth gro nd.
