V-20NMG3B
3
SAFETY PRECAUTIONS
1. T he d esi gn of th is pr od uct con ta in s sp eci al har d wa re , ma ny
circuits and components specially for safety purposes. For
con tinu ed pr ot ection , n o chan g es sh ou ld b e ma de to the o rig inal
d esign un less a uth or ized i n w ri tin g by th e ma nu fact ur er.
Rep lacem en t p ar ts m ust b e i d ent ic al to thos e u sed i n th e origin al
circu it s. S er vi ce sho uld b e p er for med by qu alif ied p ers on nel
on ly.
2. Alte r ation s of t he desi g n or cir cui tr y of t he pr od ucts sh oul d not be
made. Any design alterations or additions will void the
m anu fact ur er's w arr a nt y and w ill f ur th er r eli eve t he ma nu factu r er
of r esp onsi b il ity for per so na l i njur y or p r op er ty d am ag e r esult in g
th er efr om .
3. M an y e l ectr ical an d mech anica l p ar ts i n th e pr od ucts ha ve
special safety-relat ed characteristics. T hese characteristics are
oft en no t e vi den t f r om visua l i nsp ecti on n or ca n t he pr o tect io n
aff or de d by th em nece ssar ily b e ob tai n ed b y u sin g r ep lacem en t
com po ne nts ra ted f or hi g he r vo l tag e, watt ag e, etc. R ep lacem en t
p arts wh ic h ha ve th ese sp eci al s afet y ch ar act er ist ics ar e
identified in the parts list of Servic e manual. El ec tric al
components having su ch features are identified by shading
on the sche matic s and by (!
!!
!) on the parts list in Service
manual. The us e of a sub stitu te r ep la cem en t w hich do es n ot
h ave th e sam e saf ety ch ar act er ist ics as t he r eco mm en de d
r eplac em ent par t sh own in th e p ar ts li st of S er vi ce m an ual m ay
cause shock, fire, or other hazards .
4. Do n't shor t between the LIVE side ground and ISOL ATE D
(NEUTRAL) side ground or EARTH side ground when
repairing.
Some model's power circuit is partly different in the GND. The
diff er enc e of th e G ND i s sho wn b y th e LIV E : ( ") side GND, the
ISO LATE D( NEUTR AL) : ( #) side G ND and EARTH : ($) side
GN D. Do n't sh or t b et we en th e LIV E si d e GND an d
ISO LATE D(NEUTRAL) side GND or EARTH sid e GND an d
n ever m ea sur e w it h a m ea sur ing a ppa r atus (oscillo scop e etc.)
th e LI VE si d e GND an d IS OLA TED(NE UTRAL ) sid e G ND or
EARTH side GND at the s ame time.
If above note will not be kept, a fuse or any parts will be broken.
5. If any repair has been made to the chassis, it is recommended
th at t he B1 set ting shou l d b e ch ecke d or adju ste d ( Se e
ADJUSTMENT OF B 1 POW E R SU PPLY) .
6. T he hi gh volta ge app lie d t o th e pi ctu r e tu be mu st con for m wit h
th at sp ecifi ed i n S er vice m an ual. E xcessi ve h i gh vo lt ag e ca n
cau se an i ncr e ase in X- Ray em issi on , ar ci ng an d possib le
component damage, therefore operation under excessive high
voltage conditions should be kept to a minimum, or should be
preve nt ed. If s evere arc in g occur s, r emove t he AC power
immed i ate ly an d de ter m ine th e ca use b y vi sua l i nsp ect io n
( in cor r ect in stal lat ion, cr acke d or m elte d hi gh vo lt age har n ess,
p oor so ld ering, et c.) . To m aint ain the p r ope r min im u m le vel of
sof t X-Ray em issi on, c omp on en ts i n th e hi gh vol tag e ci rcuitr y
includ ing t he pict ur e tu be must b e t he e xact r ep lacem e nts or
alte rn at i ves ap pr ove d b y th e ma nuf act ur er of th e c om plet e
pr od uct.
7. Do n ot c hec k high volt ag e b y dr awing an arc. Use a high volt ag e
m eter or a hi g h v ol tag e pr ob e wit h a V TVM . D ischa rg e th e
picture tube before attempting meter connection, by connecting
a clip le ad to th e gr ou nd f ra me a nd c onn ecti n g th e oth er end of
the lead through a 10kΩ2W resisto r to the an od e b utt on .
8. W hen se r vi ce i s r equ ir e d, ob ser ve th e or igi na l lea d dr ess. E xtra
pr ec aut i on sh ou ld b e g i ve n t o assur e cor rect l ea d dr ess in th e
hig h vol tag e ci rcui t a r ea. W her e a s hor t cir cui t h as occu rre d,
th ose co mp on ent s tha t indica te evide nce of ove r hea ti ng sho ul d
b e r e place d. A lwa ys u se th e ma nuf act ur er's r ep lacem en t
components.
9. Isolation Check
(Safety for Electrical Shock Hazard)
Af ter r e-ass emb lin g th e p r odu ct, alw ays per f orm an i solat io n
ch eck on the expo sed me tal p ar ts of t he cabi n et ( a nte nn a
ter m ina ls, vid eo /au di o i npu t and ou tpu t t er min al s, Con tr ol kn obs,
m etal cabin et, scr ewhe ad s, ea r ph one jack, con trol shaf ts, etc.)
to be su re th e p r odu ct i s s af e t o o pe r ate with ou t d an ger of
elect rical shoc k.
(1) Dielectric Strength Test
The i so lation be tw een the A C pr im a ry circu i t an d al l me tal p ar ts
exp ose d t o th e us er , p ar ti cul arl y an y e xp os ed met al p art h aving a
r etu rn p ath to t he chass is sho uld withs tan d a volt age of 3 000 V
AC (r.m.s.) for a period of one second.
( . . . . W it hstan d a vo lt ag e of 1 10 0V A C ( r.m. s.) t o an ap pl ianc e
r ate d up to 12 0V , an d 3 00 0V AC ( r.m. s.) to an ap plian ce r at ed
200V or more, for a period of one second.)
This method of test requires a test equipment n ot generally found
in t he ser vic e trad e.
(2) Leakage Current Check
Pl ug th e A C lin e c ord d ir ect l y in to th e A C ou tl et ( d o n ot use a lin e
isolati o n tr ansf or m er du r in g thi s ch eck.) . U sin g a " Lea kag e
Cur rent Teste r", me asur e th e lea kag e cu rre nt f rom each exp osed
m etal p ar t of the ca bi ne t, p art icu l arly any e xpos ed me tal p ar t
h aving a re turn pa th to t he ch assis , t o a kn own go od ea rt h
gr ou nd (wa ter pi p e, e tc.) . An y leaka ge cur ren t m ust n ot e xceed
0.5mA AC (r.m.s.).
Howeve r, in tr op ic al ar ea , th is mu st no t exce ed 0.2 mA AC
(r.m.s.).
"
""
"Alte rnat e Che ck M ethod
Pl ug th e A C lin e c ord d ir ect l y in to th e A C ou tl et ( d o n ot use a lin e
isolati o n tr an sfor m er during t hi s che ck.) . U se an AC vo lt me ter
h aving 1 00 0 oh ms pe r volt or m ore sens it i vi ty in th e fo llowing
m ann er. C on nec t a 1 50 0Ω10W res ist or par a ll e le d b y a 0 .1 5µF
AC -type c apa cit or bet we en an expo sed met al pa rt a nd a kno wn
g ood e ar th gr o un d ( wa ter pi pe , etc.) . M eas ur e th e A C vo lt ag e
acr oss th e r es ist or wi th th e AC vo l tm eter . M ove th e r esistor
con nec tion to e ach exp ose d me tal par t, p art i cular ly a ny exp osed
m etal p ar t havi n g a r etu rn pat h to t he ch assi s, an d m easu r e th e
AC vol tag e ac ro ss the r es ist or . N o w, re verse th e pl u g i n th e AC
ou tl et and r e pe at eac h m ea surem en t. An y volt ag e me asu re d
must not exc eed 0.75V AC (r.m. s.). This c orre sponds to 0.5mA
AC (r.m.s.).
Howeve r, in tropica l area, this must not exceed 0.3V AC ( r.m. s.).
This corresponds to 0.2mA AC (r.m.s.).
0.15μF AC-T YPE
1500 Ω10W
GOODEARTH GROUND
PLACE THIS PROBE
ON E A C H EX PO SE D
ME T AL PA RT
ACVOLTMETER
(HAVING 1000 Ω/V,
OR MOR E SENSIT IVITY)
