Sharp R-212 Service Manual download pdf (Page 11)

R-212B

1000g

T1˚C

T2˚C

Heat up for 62 sec.

B POWER TRANSFORMER TEST

CARRY OUT 3D CHECKS.

Disconnect the leads to the primary winding of the power transformer. Disconnect the filament and

secondary winding connections from the rest of the HV circuitry. Using an ohmmeter, set on a low

range, it is possible to check the continuity of all three windings. The following readings should be

obtained:

WARNING: High voltages and large currents are present at the secondary winding and

filament winding of the power transformer. It is very dangerous to work near this

part when the oven is on. NEVER make any voltage measurements of the high-

voltage circuits, including the magnetron filament.

If the reading obtained are not stated as above, then the power transformer is probably faulty and

should be replaced.

CARRY OUT 4R CHECKS.

Initial temperature .................................................................................................. T1 = 11°C

Temperature after (60 + 2) = 62 sec. ..................................................................... T2 = 21°C

Temperature difference Cold-Warm.................................................................... ∆T1 = 10°C

Measured output power

The equation is “P = 70 x ∆T” ...................................................... P = 70 x 10°C = 700 Watts

JUDGMENT: The measured output power should be at least ± 15 % of the rated output power.

CAUTION: 1°C CORRESPONDS TO 70 WATTS. REPEAT MEASUREMENT IF THE POWER IS

INSUFFICIENT.

a.Primary winding ............... 1.9 ohms approximately

b.Secondary winding........... 154 ohms approximately

c.Filament winding .............. less than 1 ohm

C HIGH VOLTAGE RECTIFIER ASSEMBLY 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 infinite in one direction and more than 100 kΩ in the other direction.

CARRY OUT 4R CHECKS.

NOTE: FOR MEASUREMENT OF THE RESISTANCE OF THE RECTIFIER, THE BATTERIES OF

THE MEASURING INSTRUMENT MUST HAVE A VOLTAGE AT LEAST 6 VOLTS, BE-

CAUSE OTHERWISE AN INFINITE RESISTANCE MIGHT BE SHOWN IN BOTH DIREC-

TIONS.

TEST PROCEDURES

PROCEDURE

LETTER

COMPONENT TEST

HIGH VOLTAGE RECTIFIER

1 2 ... 6 7 8 9 10 11 12 13 14 15 16 ... 35 36

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Sharp R-212 Service Manual Page 11

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