Precautions For Using Lead-Free Solder - Sharp R-7500AT Service Manual

Commercial microwave oven

Table of Contents

R-7500AT

Oven should not be run empty. To test for the presence of microwave energy within a cavity, place a cup of cold water on the ceram -

ic oven floor, close the door and set the power to 100% and set the microwave timer for one (1) minute. When the one minute has

elapsed (timer at zero) carefully check that the water is now hot. If the water remains cold carry out Before Servicing procedure and

re -examine the connections to the component being tested.

When all service work is completed and the oven is fully assembled, the microwave power output should be checked and microwave

leakage test should be carried out.

Some normal boards are found in board units that have been returned due to oven failure. So, most of board replacements may arise

from poor harness connection. Accordingly, before replacing any board that was judged to require its replacement, use the following

procedure to re-check that the connection terminal of a connector has been properly inserted:

1. When the connectors have been incorrectly inserted to the control unit.

CONNECTOR

The oven can not be powered on.Antenna motor(s) does not run.Blower motor(s) does not run.

CN -A

CN -B

The oven can not be powered on.No heating can be done.LED light does not illuminate.

No indication, no key insertion and no buzzer sound.

CN -D,CN -F

The power level can not be varied.MGT thermistor(s) does not work.Magnetron(s) does not work.ER -

CN -G

ROR(s) shows.

2. When latch switch adjustment is incorrect

When latch switch adjustment is incorrect, symptoms such as no heating, no heating start, no activation even with start button

pressed, etc. will occur.

Employing lead-free solder

The "Main PWB" of this model employs lead-free solder. This is indicated by the "LF" symbol printed on the PWB and in the service

manual. The suffix letter indicates the alloy type of the solder.

Example:

Indicates lead-free solder of tin, silver and copper

Using lead-free wire solder

When repairing a PWB with the "LF" symbol, only lead-free solder should be used. (Using normal tin/lead alloy solder may result in

cold soldered joints and damage to printed patterns.)

As the melting point of lead-free solder is approximately 40ºC higher than tin/lead alloy solder, it is recommend that a dedicated bit is

used, and that the iron temperature is adjusted accordingly.

Soldering

As the melting point of lead-free solder (Sn-Ag-Cu, Sn-Cu-Ni) is higher and has poorer wettability, (flow), to prevent damage to the

land of the PWB, extreme care should be taken not to leave the bit in contact with the PWB for an extended period of time. Remove

the bit as soon as a good flow is achieved. The high content of tin in lead free solder will cause premature corrosion of the bit. To re -

duce wear on the bit, reduce the temperature or turn off the iron when it is not required.

Leaving different types of solder on the bit will cause contamination of the different alloys, which will alter their characteristics, mak -

ing good soldering more difficult. It will be necessary to clean and replace bits more often when using lead-free solder. To reduce bit

wear, care should be taken to clean the bit thoroughly after each use.

BEFORE REPLACING THE PRINTED WIRING BOARD