Tipps - Philips N4520 Capstan Motor

[Peter.H]

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

[Nikola]

HI,

I also have this recorder and I'm very satisfied with it. However, because I did not want to motor to rotate thousand s of hours while the unit is only switched on but not playing, I have modified the circuits in a way, the Teac X2000 does this:
The motor stops to rotate, if the tension arms are in the low edge position for a while. This allows for a warmed-up recorder staying nicely illuminated in standby, but the motor is not turning.

[Peter.H]

Hallo,

Thank you for your reply. I agree that these recorders are very nice machines, because I have the half and quarter track versions. ( but not the most robust taperecorder!! )
It is a very clever idea to use the tension arms to turn off the motor:-)
Maybe you used a 555 timer, or something similar?

Peter.

[Nikola]

it is a very simple circuit with only one CMOS IC 4093 and few passive components. Unfortunately my scanner does not work now. I will post it at some later time.

[atb.oomen]

Yes, I would also like to see the schematic diagram from the circuit that shutts off the capstanmotor when the tension arms are in the 'down'-position.

[hanns-d.pizonka]

Nikola postete
it is a very simple circuit with only one CMOS IC 4093 and few passive components. Unfortunately my scanner does not work now. I will post it at some later time.

Hallo Nikola,
kannst Du uns allen mit der Aussenbeschaltung des 4093 inzwischen weiterhelfen? Würde mir auch für meine A77HS weiterhelfen, denn warum soll der Tonmotor nachts nach erfolgter Aufnahme immer noch weiterlaufen, wenn der rechte
Wickelteller voll mit Band ist und meine Aufnahme schon längst erledigt ist. Heute ja ist als "Energiesparer" auch bei mir das Motto angesagt: Spart Strom (-Energie).

Grüsse
H A N N S -D.

[Nikola]

Hallo,

ich melde mich in ein Paar Tagen dazu.
Bitte noch ein bischen Geduld.
Ich will es auch bei meiner 4522 einbauen, also muß ich mir das sowieso wieder anschauen...

Grüße

Nikola