Merrychef MD0750, MD1000 Service Manual

Merrychef

MD-SERIES

SERVICE MANUAL

Part No. 32Z3329 Issue No. 6

For all MD-Series models manufactured from January 2001

CAUTION MICROWAVE EMISSIONS

DO NOT BECOME EXPOSED TO EMISSIONS FROM THE MICROWAVE

GENERATOR OR PARTS CONDUCTING MICROWAVE ENERGY

Page 1 MD Series Ovens 32Z3329 Issue 6

SERVICE MANUAL

Table of Contents

Safety Code...........................................................................3

Product Specifications ..........................................................4

Installation Instructions ..........................................................5

Error Codes and Diagnostics.................................................6

Power Output Testing to BS EN 60335-2-90.........................7

Power Output Testing............................................................8

Power Transformer Test........................................................8

High Voltage Capacitor Test..................................................9

High Voltage Rectifier Test....................................................9

Magnetron Test .....................................................................9

Exploded View ....................................................................10

Door Assembly ....................................................................11

Door Replacement and Adjustment.....................................12

Door Servicing .....................................................................13

Door Interlock operation ......................................................14

Membrane Panel Circuit ......................................................15

Input Wiring Details .............................................................16

Part Number Identification List ...................................... 17-18

Wiring Diagram ...................................................................19

Appendix 1: Cleaning procedure .........................................20

Appendix 2: Door interlock All Models before Jan 2007......21

Manual Corrections and Modifications ................................22

From January 2007 only the MD1800 Microwave Oven model is
being manufactured. All the other MD Series ovens are
discontinued.
Note that the MD1800 currently in production has a different door
interlock system to the earlier model and can be identified from the
handle which is solid and does not have the door catch release
mechanism on the inside face of the handle.

Merrychef Limited,
Station Road West,
Ash Vale, Aldershot,
Hampshire, GU12 5XA
United Kingdom
Tel: [phone] Fax: [phone]
Internet address: http://www.merrychef.com

E-mail: [e-mail] or [e-mail]

Page 2 MD Series Ovens 32Z3329 Issue 6

SAFETY CODE

This manual is designed to assist engineers who have been on a recognised product familiarisation
and training course run by Merrychef Limited. It has been prepared to offer technical guidance for the
Merrychef MD Series Commercial Microwave Ovens.

Please remember that it is wiser not to attempt a service task if you are unsure of being able to
complete it competently, quickly, and above all safely.

To avoid injury to yourself, and to protect the appliance from possible damage, please follow this
Safety Code when servicing these ovens.

Before attempting to repair the oven, check it for microwave leakage.

Check that the oven is not emitting microwaves, even when supposedly not in operation.

Check that the oven is not operating continuously, whether the display indicates cooking
or not.

Always discharge the HT capacitors before working on the oven using a suitably
insulated 10 MΩ Resistor

Before removing the rear cover from the oven, ensure you do the following:

• Switch off the mains supply and remove the plug from the wall socket.

or

• If the oven is hard wired, ensure that the power is turned off at the isolator switch.

Note: the oven does NOT have an On/Off switch.

Upon completion of a service on an MD Series oven, or before reconnecting the appliance to the
mains supply for testing, check all of the following points:

• All internal electrical connections are correct.

• All wiring insulation is correct and is not touching a sharp edge.

• All Earth connections are electrically and mechanically secure.

• All four door safety interlocks are secure and mechanically sound.

• The door operation is smooth.

• The door activates all four of the door interlock switches in the correct order.

• All fuse-holder safety covers are correctly fitted.

Before finishing the service call, recheck the following points:

• All of the electronics are functioning correctly, and all of the touch pads are working.

• The power output of the oven is correct (see pages 7 & 8 ).

• Microwave emission is below permissible limit - 5mW/cm² (see BS EN 60335-2-90:).

• Oven has correct 50mm air gap all round. Air flow should not be restricted.

Page 3 MD Series Ovens 32Z3329 Issue 6

Product specifications

Model Number: MD + Power + Voltage + Frequency + Country

For example: MD1800C25EX
Model MD 1800 (1000W) , 220-230V, 50Hz, Export model

Only Model MD1800 is currently manufactured

Model prefix Voltage Frequency Country

MD

Power Requirements

Power Output
Microwave 100%

External Dimensions

Internal Dimensions

Model Number

750
1000
1400
1800

MD 075045CUK

MD1000C45UK

MD1000C25EX

MD1400C45UK

MD1400C25EX

MD1800C45UK

MD1800C25EX

MD0750

MD1000

MD1400

MD1800

Height

Width

Depth

Height

Width

Depth

Capacity

2 = 220-230V a.c.
4 = 230-240V a.c

230-240V ac 50 Hz 13.0A Single Phase 2 Wire + Earth
230-240V ac 50 Hz 13.0A Single Phase 2 Wire + Earth
220-230V ac 50 Hz 14.2A Single Phase 2 Wire + Earth
230-240V ac 50 Hz 13.0A Single Phase 2 Wire + Earth
220-230V ac 50 Hz 14.2A Single Phase 2 Wire + Earth

230-240V ac 50 Hz 13.0A Single Phase 2 Wire + Earth
220-230V ac 50 Hz 14.2A Single Phase 2 Wire + Earth

750W ( IEC 705 )
1000W ( IEC 705 )
1400W ( IEC 705 )

1800W ( IEC 705 )

335mm ( Plus 50mm minimum clearance above )
510mm ( Plus 50mm minimum clearance each side )
415mm ( Plus 50mm clearance behind )

210mm
330mm
330mm
23 litres (0.81 ft³)

5 = 50 Hz
6 = 60 Hz

UK

EX = export

Weight

Construction

Settings

Nett

Gross packed

Cavity & Casework 304 Stainless Steel

Microwave

Timer

30kg
35kg

100%, 75%, 50%, progressive Defrost
Up to 9 minutes 59 seconds
Up to 3 cooking stages of up to 9 minutes 59 seconds each
(Programmed)

Control System Wipe-clean touch pad operating microprocessor based control system.

Direct readout of time and power set.
10 Pre-programmed cooking sequences accessed by just two key
presses.

Safety Features Four door interlock switches.

Cavity Overheat Sensor.
Magnetron Overheat Sensor.

Additional Features

• Easy-to-use multistage programming.

• Manual and Pre-programmed mode always available

• Magnetron soft-start circuit for increased life and faster activation.

• Multiple product facility.

Page 4 MD Series Ovens 32Z3329 Issue 6

Installation instructions

Power Supply Requirements

The oven should be connected to a suitable electricity supply, which can cope with the switching­on surge that occurs with certain types of catering equipment, such as microwaves. Because of
this requirement, we strongly recommend that a separate, suitably rated supply is installed for the
oven.

The supply for the oven should be fitted with a Type "C" circuit breaker, rated at 16A.

Positioning the Oven

In order to maintain adequate ventilation for air intake and exhaust, and to allow access for
cleaning filters, you must allow a minimum of 50mm clearance all around the oven. Air intake
temperature should not exceed 35°C - excessive temperature can lead to reduced operating duty
cycle or premature ageing of internal components.

ALWAYS Place containers in the cavity carefully - impact damage may chip the oven shelf

NEVER Install an oven above fryers, grills, griddles or any other major heat source

NEVER Stack machines on top of each other without using the stacking adapter provided

stacking adapter

maximum

3 ovens

in a stack

Page 5 MD Series Ovens 32Z3329 Issue 6

Error codes and diagnostics

The MD series oven will identify some of the most common problems by flashing an error message
code in the time display window.

These are the error messages, and suggestions for repairing them.

1

1

Door not fully shut

2

Possible electrical fault

No time has been set

2

Invalid time has been set.

3

Invalid program has been
set

4

Memory failure running a
Program

Close door fully

Check microswitch door circuit
Check microswitch connection
to PCB
Check ribbon cable
Check relay PCB & logic PCB

Set a time

Set a valid time

Use call-back to check program

Re-Program Pad,
if fault repeats replace logic
PCB

Page 6 MD Series Ovens 32Z3329 Issue 6

Procedure A - Power Output Test in accordance with

BS EN 60335-2-90 Annex AA

This test is given in the BSI test standard for microwave ovens. It is reproduced below - not so that
you can follow it, but to show you why it is impractical in normal conditions. A simplified procedure,
which gives a good approximation to the BSI power output, is given in Procedure B which follows.

Note: This test can only be carried out on a COLD oven. If the oven has been operating, even for
only a few seconds, the power given will be lower than the oven rating. This test must also be
carried out at a stable voltage - the voltage in most kitchens varies considerably even within the
period of the test. If the oven has been operating, go to Procedure B.

You will need:

A thermometer capable of reading to ±0.1°C.
A cylindrical borosilicate glass container, 190mm diameter, with a wall thickness of
3mm or less.
A calculator.
A set of scales capable of reading 1kg to an accuracy of ± 1g.
A glass or plastic stirrer.
A jug capable of holding over 1 litre of water.
Drinkable water which is at a temperature of 10°C ± 1°C.
A “Variac” or similar variable transformer capable of supplying the oven to ensure
a stable voltage.

WARNING: The Borosilicate Glass container has thin walls and is therefore fragile

- take care not to break it during use.

Method

A cylindrical container of borosilicate glass is used for the test. It has a maximum thickness of
3mm, an external diameter of approximately 190mm and a height of approximately 90mm. The
mass of the container is determined.

At the start of the test, the oven and the empty container are at ambient temperature. Potable water
having an initial temperature of 10°C ± 1°C is used for the test. The temperature of the water is
measured immediately before it is poured into the container.

A quantity of 1000g ± 5g of water is added to the container and its actual mass obtained. The
container is then immediately placed in the middle of the oven shelf which is in its lowest normal
position. The appliance is supplied at rated voltage and operated at the maximum power setting.
The time for the water temperature to attain 20°C ± 2°C is measured. The oven is then switched off
and the final water temperature is measured within 60seconds.

NOTES:

1 The water is stirred before its temperature is measured.
2 Stirring and measuring devices are to have a low heat capacity.

The microwave power output is calculated from the formula:

P =

where

P is the microwave power output, in watts;
M

is the mass of the water, in grams;

W

M

is the mass of the container, in grams;

C

T

is the ambient temperature, in °C;

0

T

is the initial temperature of the water, in °C;

1

T

is the final temperature of the water, in °C;

2

t is the heating time in seconds, excluding the magnetron filament heat-up time.

4.187 MW (T2-T1) + 0.55 MC (T2-T0)

t

Page 7 MD Series Ovens 32Z3329 Issue 6