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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 22nd Feb 2020, 10:21 am   #1
Antonello
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Default Philips N4450

Hi friends, I apologize in advance for my poor English
I am Italian, precisely I live in Sardinia
i have a philips n4450 recorder
he was stationary 15 years locked in an attic
put it into operation after putting the new belts on
a problem that I immediately encountered and that the right motor stopped after 20 seconds causing the tape to come out of the reel
I solved it by repairing the tape tension card
then there was another problem a channel did not sound and I found a blown fuse following the blue wires on the board they took me to 2n3055
it was shorted, I replace it but the fuse blows the same
then I thought to check also the other 2n3055 and also the latter was short
I have not soldered a new 2n3055 and now the fuse does not burn out so everything should work by putting in a new transistor.
a problem that I do not get to grips with and the bulbs
when it was turned on for the first time, everything except those of the programmer turned on
now some have suddenly burned out
the rest do not turn on
I would like to know where I need to check to check the voltage of the bulbs
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Old 22nd Feb 2020, 7:32 pm   #2
DMcMahon
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Default Re: Philips N4450

Your English is great, a million times better than my Italiano !

Not familiar with Philips but it looks a very good R2R and quite complex.

Not yet had time to see where the 2N3055 power transistors are, but see that the main bulbs are fed with a +26 volts supply from the power supply, so important to measure the voltage arriving at the bulbs to see if it is too high.

David
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Old 23rd Feb 2020, 3:27 pm   #3
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Default Re: Philips N4450

Can now see the 2N3055 transistors on the output stage of the Power Output Unit that drives the loudspeaker (s).

There is the +26 volt supply and a -ve 26 volt supply across these transistors via 2 amp fuses, so think you should first check out all the supplies at the power supply.
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Old 28th Feb 2020, 4:13 pm   #4
Antonello
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Default Re: Philips N4450

So in the meantime, thank you for replying
I'll explain what happened
after connecting the other 2n3055
I turned on with two speakers connected and the sound that is heard and terrible
as I turn up the volume everything feels distorted saturated
I measured the voltages on the fuses
I did so I removed a fuse and connected the tester terminals I made the measurement for both fuses and I have the + and - 26 volts
in the other ending I don't have these tensions...

I also have another problem
if I put the recorder in amplifier only mode the capstan motor runs without control while it should stop
and then I made another discovery if I keep the stop button pressed the lights come on
releasing the stop button they go off
there is something that does not work well
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Old 1st Mar 2020, 9:52 am   #5
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Default Re: Philips N4450

Hello Antonello,

It is getting confusing ?

I do not understand what you mean by "I made the measurement for both fuses and I have the + and - 26 volts in the other ending I don't have these tensions..."

Do you mean you do not have those voltages at the other end, if so,then is this not because you removed the fuse for the measurement ?

For the lamps to originally blow it sounded like the associated supply voltage was too high or maybe a voltage surge had taken the lamps out.

For the transistors to fail sounds like they may have been taking too much current.

I would recheck all the DC supply voltages and also check that the 1 ohm resistors on the emitter of the 2N3055s (2 resistors in parallel) have not burnt out and shorted.

For the distorted sound the problem could be elsewhere but the fact that the 2N3055 output transistors have previously blown I would first check the 1 ohm resistors.

I have not had time to look at your other problem symptoms.

David
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Old 1st Mar 2020, 11:57 am   #6
Antonello
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Default Re: Philips N4450

Hi david thanks for replying again.
I solved some problems.
2N3055 were shorted on a channel, replaced now everything works again, but I have the problem of distortion both channels.

I am proceeding to replace the capacitors on the amplifier board' because they are all out of range, example a capacitor that should be 1000uf and 1600uf another 10uf and 28uf are all like this and certainly live creating a mess. After I have changed them all I will let you know.

Tomorrow I have to go get those from 680uf.

Thanks again, Antonello.
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Old 1st Mar 2020, 9:19 pm   #7
DMcMahon
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Default Re: Philips N4450

Hello Antonello,

Electrolytic capacitors can/do increase their capacitance with age, sometime without any apparent degradation in performance. Hopefully in your case it will help the situation.

David
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Old 2nd Mar 2020, 3:54 pm   #8
nicola.ghinassi
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Default Re: Philips N4450

HAllo Antonello. My name is Nicola, i live in Romagna. I have too an N4450. If you want, you can write me in PM.
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Old 10th Mar 2020, 2:04 pm   #9
Antonello
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Default Re: Philips N4450

Hi David then I fixed my philips n4450
now the lights are turned on by pressing the main button the capstan motor stops in Amp mode
and the distortion is gone
after replacing all electrolytes
on the motherboard
I am using it only with a final card because in the other of the right channel there is still distortion I think it is a small 22 nanofarad capacitor that lacks
with the oscilloscope I followed the signal and the distortion stops there
the lights did not turn on because the black wire n ° 12 starting from behind the keyboard was interrupted on the k5 connector.
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Old 10th Mar 2020, 3:57 pm   #10
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Default Re: Philips N4450

H Antonello,

Excellent progress, good diagnostics from yourself, well done ! thank you for the updates.

David
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