Sharp R-4A52 Service Manual page 12

R-4A52
R-4E52
TEST PROCEDURES (CONT'D)
PROCEDURE
LETTER
COMPONENT TEST
Example: Tl = 20°C, T2 = 21 "C
initial temperature ~~
Temperature after 1 min. 52 sec.
Temperature difference Cold-Warm
---
Mean temperature rise LIT
i
T
T
Measured output power
The equation is as follows:
P= 75 x AT
Tl '=lO"C T2=11"C
I
Tl = 20°C T2 = 21 "C
,!LTl =lO"C LIT~=IO"C /
-------------,
LIT = (LIT1 + LLT2) / 2 !
= (10°C + IOOC) / 2 j
= 10°C
P= 75 x 10°C
= 750 Watts
-I
NOTE:
The measured output power should be at least +I5 % of the rated
output power.
CAUTION: 1 "C CORRESPONDS TO 75 WATTS.
REPEAT MEASUREMENT IF THE POWER IS INSUFFICIENT.
(Tl OC) lT2 OC) (T2 OCI
Heat up for 1 min. 52 sec.
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 circuits, including the magnetron
filament.
CARRY OUT D 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 -------
b.
---l .42 ohms approximately.
Secondary winding - - - - - - -78.9 ohms approximately.
c. Filament winding ---------less than 1 ohm.
If the reading obtained are not as stated above, then the power transformer is probably faulty and
should be replaced.
CARRY OUT 4R CHECKS
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