Sharp R-8R51 - Page 18

R-8RST(W). -
R-8R51(B) :
TEST PROCEDURES (CONT’D)
PROCEDURE
LETTER .« COMPONENT TEST
Cc ‘HIGH VOLTAGE RECTIFIER ASSEMBELY TEST
HIGH VOLTAGE RECTIFIER TEST.
CARRY OUT 3D CHECKS.
Isolate the high voltage rectifier assembly from the HV circuit. The high voltage rectifier can be
tested using an ohmmeter set to its highest range. Connect the ohmmeter across the terminal
B+C of the high voltage rectifier and note the reading obtained. Reverse the meter leads and
note this second reading. The normal resistance is intinte in one. as airection and mor than 100
kin the other direction. $$
CARRY OUT 4R CHECKS ar fie ae Sate B
ASYMMETRIC RECTIFIER TEST “ASYMMETRIC Lg)
; HIGH VOLTAGE RECTIFIER
CARRY OUT 3D CHECKS. 7 c
Isolate the high voltage rectifier assembly from the HV circuit. The asymmetric rectifier can be
tested using an ohmmeter set to its highest range. Connect the ohmmeter across the terminals
‘A+B of the asymmetric rectifier and note the reading obtained. Reverse the meter leads and note
this second reading. If an open circuit is indicated in both directions then the asymmetric rectifier
is good. Ifa asymmetric rectifier is shorted in either direction, then the the asymmetric rectifier
is probably faultly and must be replaced with the high voltage rectifier. When the asymmetric
rectifier is defective, check whether magnetron, high voltage rectifier, high voltage wire or fila-
ment winding of the power transformer is shorted.
CARRY OUT 4R CHECKS
NOTE: FOR MEASUREMENT OF THE RESISTANCE OF THE RECTIFIRE, THE BATTERIES
OF THE MEASURING INSTRUMENT MUST HAVE A VOLYAGE AT LEAST 6 VOLTS,
BECAUSE OTHERWISE AN INFINITE RESISTANCE MIGHT BE SHOWN IN BOTH
DIRECTIONS. —
D HIGH VOLTAGE CAPACITOR TEST
CARRY OUT 3D CHECKS.
A. Isolate the high voltage capacitor from the circuit.
B. Continuity check must be carried out with measuring instrument which is set to the highest
resistance range.
C. A normal capacitor shows continuity for a short time (kick) and then a resistance of about
10 KQ after it has ben charged.
D. A-short-circuited capacitor shows continuity all the time.
E. An open capacitor constanlly shows a resistance about 10 MQ because of its internal 10
MQ resistance.
F. Whe the internal wire: is apened in the high voltage capacitor, the capacitor shows an infinite
resistance °
G. The resistance across all the terminals and the chassis must be inifinte when the capacitor
is normal.
if incorrect readings are obtained, the high voltage capacitor must be replaced.
‘CARRY OUT 4R CHECKS
oe SWITCH TEST
CARRY OUT 3D CHECKS. .
Isolate the switch to be tested and using an ohmmeter aneeK between the terminals as described
in the following table.
Plunger Operation COM to NO COM to NC
Relessed «| oc | ~SG.
| Depressed of SC TOO
Terminal Connection of Switch COM: Common terminal
NO; Normaliy open terminal
NC; Normally closed terminal .br
S.C.; Short circuit,
0.C.; Open circuit
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