06.02.2007, 14:03
Hallo,
I have a Philips N4520 and I have had many problems with the capstan motor and its driver PCB.
The motor output device, IC407 µA78MGCU1 on the servo board, failed twice. This is an obsolete voltage regulator, so it is not too easy to buy.
The first symptoms were that all of the decimal points on the display were lit on 38 cm/s, which indicates that the circuit is 'out of lock'. After a short time the IC407 failed, causing the motor to stop.
I discovered that the cause of this failure is the motor drawing too much current.
The motor was removed from the maschine and was opened up (which required some bending of the metal housing).
Below are some pictures of my findings:-
The high current was caused because of metal dust from the brushes and commutators short-circuiting in between the gaps. This dust was cleaned with a brush and a small amount of alcohol.
I made some current readings - The motor was connected to a 12 Volt power supply. Before the motor was cleaned of the metal dust the current was 150 mA at 12 Volts. After cleaning the metal dust the reading was <10 mA at 12 Volts.
I think that this motor problem is because the Capstan motor turns all of the time that the maschine is switched on, which might be thousands of hours!?
Now my N4520 is working:-)
Maybe this will help others that have IC407 that keeps failing?
Peter.h
I have a Philips N4520 and I have had many problems with the capstan motor and its driver PCB.
The motor output device, IC407 µA78MGCU1 on the servo board, failed twice. This is an obsolete voltage regulator, so it is not too easy to buy.
The first symptoms were that all of the decimal points on the display were lit on 38 cm/s, which indicates that the circuit is 'out of lock'. After a short time the IC407 failed, causing the motor to stop.
I discovered that the cause of this failure is the motor drawing too much current.
The motor was removed from the maschine and was opened up (which required some bending of the metal housing).
Below are some pictures of my findings:-
The high current was caused because of metal dust from the brushes and commutators short-circuiting in between the gaps. This dust was cleaned with a brush and a small amount of alcohol.
I made some current readings - The motor was connected to a 12 Volt power supply. Before the motor was cleaned of the metal dust the current was 150 mA at 12 Volts. After cleaning the metal dust the reading was <10 mA at 12 Volts.
I think that this motor problem is because the Capstan motor turns all of the time that the maschine is switched on, which might be thousands of hours!?
Now my N4520 is working:-)
Maybe this will help others that have IC407 that keeps failing?
Peter.h