Job Number

0012-14

Equipment type

Electronic hot air cooking oven (like the 'Grillioso')

Maker + Model #

Easycook custom 737

Made in

?

Comments

Previously was for service but it was not repaired

BAD

1

Completely dead, no power up

GOOD

1

Hmmm…..

Full repair description and observations

1

First the ohmage of the motor coils and heating elements were checked to exclude expensive faults. The motor gave 143 Ohms, and the heating element was 43 Ohms; no o/c.

2

Since there was no power, the power supply section was tested, and found that there was no output on the rectifying diodes.

3

The mains transformer was checked and found that there was an open circuit in the primary, and a 2.7k in the secondary. On removing it from the pcb, it was visibly bad ridden.

4

A new encapsulated transformer was bought but did not fit in the pcb for a question of few millimetres. The pcb was made widened by liming the edges until the transformer pins fitted in.

5

It was held firmly by Impact evo-stick glue, and the pins were soldered accordingly.

6

On powering up, voltage came on the rectifiers, but there was no Led display. There was a 5V voltage regulator open circuit, and when replaced everything powered up. ^

7

The motor, fan, and heating elements were fitted into place, and powered up. After about 30sec, the protection circuit became activated!

8

This heating element was eliminated, and when powering, the motor and display worked perfectly without tripping the protection circuit. The heater is hence suspected to be short.

8

The heater was connected directly to the mains supply (without earth) and let to heat up. The a.c. voltage for checking for short circuits was tested by placing one DVM probe at one end of the heat filament, and the other with the outer surface of the filament. When heating the voltage rose to 150v to 200V a.c - this caused the tripping. Eventually, when the heater was red hot, the voltage fell steadily to 110V. This voltage would not trip up. Since the heater filament was not used up for very long time, humidity gathered between filament and outer casing and served as a conductor to short up. On heating, this humidity was removed and the short was eliminated.

9

The heater was assembled back, to place and the hot air oven worked perfectly without triggering the protection circuit.

Repair summary

MAINS A.C. TRANSFORMER OPEN CIRCUIT

OPEN VOLTAGE REGULATOR

Precautions, fouls and advises

1

When a heater is not used for a very long time, it may get humidity in the insulating material between inner heating coil, and outer protective metal tube. This could cause a short to earth. Heating the element to red hot for approx 3 mins will evaporate all humidity and eliminate the short.

To reservoir Capacitor

To reservoir Capacitor

1

Here are some notes of how to fit 0v/6v/0v/6v ac mains transformer to suit 3 applications:

 1) 6V full wave rectification

 2) 12V half wave rectification

 3) 6V parallel (double power) half wave rectification.

1)

2)

3)

	To reservoir Capacitor

 

2

This little oven contained an intel microprocessor!! ® 1977. The 4 ICs found where:

1) DBL393 - 9348C (8-pin)

2) MOC 3023 - 9506 (6 -pin) [Motorola]

3) Ph BY136 - 600E.02, p9441 (3-pin)

4) P8049AH 8974 "TALL & STOUT", IP73700-01 (40pin)  [Intel]