B: Power Transformer Test; C: High Voltage Rectifier (1) And/Or (2) Test - Sharp R-1900J Service Manual

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Operation and cooking manual (33 pages)

Table Of Contents

Table of Contents

Room temperature .................................................................... To = 21°C

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

Temperature after (22 + 3) = 25 sec. .......................................... T2 = 21°C

Temperature difference Cold-Warm .....................................

Measured output power

The equation is "P = 190 x

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

CAUTION: 1°C CORRESPONDS TO 190WATTS REPEAT MEASUREMENT IF THE POWER IS INSUFFICIENT.

1000g

T1 C

[2] B: POWER TRANSFORMER TEST

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 cir-

cuits, including the magnetron filament.

1. CARRY OUT 3D CHECKS.

2. 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 winding. The following readings should be

obtained:

a.Primary winding -------------------- approximately 1.3 Ω

b.Secondary winding --------------- approximately 76 Ω

c.Filament winding --------------------------- less than 1 Ω

If the readings obtained are not stated as above, then the power transformer is probably faulty and should be replaced.

3. CARRY OUT 4R CHECKS.

[3] C: HIGH VOLTAGE RECTIFIER (1) AND/OR (2) TEST

1. HIGH VOLTAGE RECTIFIERFTEST

1. CARRY OUT 3D CHECKS.

2. 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 100k ohms in the other direction.

3. CARRY OUT 4R CHECKS.

2. ASYMMETRIC RECTIFIER TEST

1. CARRY OUT 3D CHECKS.

2. Isolate the high voltage rectifier assembly from the HV circuit. The asymmetric rectifier can be tested using an ohmmeter set to its highest range

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. If the asymmetric rectifier is shorted in either direction, then the

asymmetric rectifier is faulty and must be replaced with high voltage rectifier. When the asymmetric rectifier is defective, check whether magne-

tron, high voltage rectifier, high voltage wire or filament winding of the power transformer is shorted.

3. CARRY OUT 4R CHECKS.

NOTE: Be sure to use an ohmmeter that will supply a forward bias voltage of more than 6.3 volts.

T" ...................... P = 190 x 10°C = 1900 Watts

1000g

Heat up for 25 sec.

ASYMMETRIC

RECTIFIER

T1 = 10°C

HIGH VOLTAGE

RECTIFIER