Sharp R-3A56, Service Manual

R-3A56

11

TEST PROCEDURES (CONT'D)

B

POWER TRANSFORMER TEST

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

winding 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.

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:

a. Primary winding ................... approx. 1.73 

Ω

b. Secondary winding ............... approx. 104.7 

Ω

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

Ω

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

CARRY OUT 4R CHECKS.

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 k

Ω

 in the other direction.

Example

Initial temperature ............................................................................. T1 = 23˚C   T2 = 24˚C
Temperature after 1 min. 51 sec. ..................................................... T1 = 33˚C   T2 = 34˚C
Temperature difference Cold-Warm ..............................................

∆

T1 = 10˚C  

∆

T2 = 10˚C

Mean temperature rise 

∆

T .........................

∆

T  = (

∆

T1 

±

∆

T2) / 2 = (10˚C+10˚C) / 2 = 10˚C

Measured output power
The equation is P= 75 x 

∆

T ........................................................ P= 75 x 10˚C = 750 Watts

NOTE:  The measured output power should be at least 

±

 15 % of the rated output power.

CAUTION: 1˚C CORRESPONDS TO 75 WATTS. REPEAT MEASUREMENT IF THE POWER IS

INSUFFICIENT.

COMPONENT TEST

PROCEDURE

LETTER

1 l

1 l

(T1  C)

(T2  C)

1 l

1 l

(T1  C)

(T2  C)

Heat up for 1min. 51 sec.