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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 31st Oct 2017, 5:10 pm   #1
TonyDuell
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Default Philips N4510 reel motor

I am trying to repair a Philips N4510 and have had a disaster. I stripped the deck mechanism (apart from the heads) and cleaned the parts and then decided to check the motors. One of the reel motors was mechanically stuck, but by turning the pulley back and forth it started to spin by hand.

Alas it would not spin electrically, it drew no current from my bench PSU. So I prised off the bottom cover of the motor (possibly a bad idea but I had little to lose). It appears to be an ironless rotor, face commutator and leaf springs for the brushes in the bottom cover.

Anyway, it's open-circuit between all pairs of segments of the commutator. I can't work out how to get the motor further apart (I would consider having a go at rewinding it, I guess....)

Does anyone have any suggestions as to a possible replacement? I will put a 'wanted' request in the appropriate section just in case, but...
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Old 7th Nov 2017, 12:34 pm   #2
TonyDuell
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Default Re: Philips N4510 reel motor

A little more on this....

There are some stakes (formed with a punch) around the spindle. I carefully drilled these with a 1.5mm bit and found they retain a washer over the bearing. Under it was a lot of Evil Goo from the old drive belt, which was why it was mechanically stuck. Whether that caused the electrical problems I don't know.

You can press the spindle out from the bottom (commutator) end. The commutator is a separate part, then hanging on the winding wires. NEVER press the spindle from the top (drive) end, you will force the commutator away from the windings and break connections. Whether that was done to this motor at some point I don't know, it's possible it's been apart before.

With the spindle pressed out, the winding assembly (ironless rotor) is loose but it will not come out. It's catching on the field magnet. I cannot work out how it was assembled, and thus how to dismantle it. Does anyone know?
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Old 15th Nov 2017, 7:48 pm   #3
TonyDuell
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Default Re: Philips N4510 reel motor

A friend managed to get me an original Philips motor. Although it didn't look identical to the old one, it fitted perfectly, and seemed to work.

I then went through the electronics.... Firstly, never plug the Recorder Stop and Motor Stop modules into each others connectors. You will blow transistors if you do. Do not ask how I discovered this. Having fixed that, the motor seemed to work, but neither reel motor (original or replacement) would restart reliably if the tape got too tight for too long. A tweak of the tape tension presets cured that, oddly both needed to be turned to about the same position to get the right voltages as in the service manual. So it appears that the replacement motor is electrically the right one.

I had already replaced the leaky AC128s with 2N3906s. They are marginal, the pinch solenoid draws rather too much current and one of the transistors was going way out of saturation with a C-E drop of about 5V. This caused the control logic to get confused. I will fit some heftier transistors, but for the moment I have reduced the 2k7 base resistor (actually by paralleling it with a 2k2) which has helped. The machine will now work, play tapes, etc.

Two problems remain. One is cosmetic, the trim strip for the knob on the mains switch needs repainting. The other is that the pulley on the tape counter has a radial crack, for which the obvious solution is to turn a replacement. When it is slightly warmer in the garage...

Oh and one more hint. The N4510 is essentially an N4418 without power amplifiers. The N4510 manual on the web is not very complete. I recomend downloading the N4418 manuals as well. You need the N4510 manual for details of the audio circuitry, but the N4418 manual is a lot clearer on the mechanism and control sections.
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Old 16th Nov 2017, 1:46 pm   #4
Welsh Anorak
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Default Re: Philips N4510 reel motor

I always found the driver transistors on this and similar Philips electronic machines were inadequate, especially when the motors aged. Uprating them is a very sensible idea - something in the BD series is possible.
Glad you found a motor - does your friend stock hens' teeth as well?
Glyn
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Old 16th Nov 2017, 6:14 pm   #5
TonyDuell
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Default Re: Philips N4510 reel motor

I have no idea how my friend found the motor, but I asked various people if they had any idea where to get one and he managed it. I think many of us have rare parts in the junk box (I certainly do).

The driver transistors that I am having problems with were originally AC128s. THey are cross-coupled to BC147s (or BC547s) to make flip-flops. One of these flip-flops (and thus the AC128) drives the pinch roller solenoid directly. A 2N3906 (which is what I currently have in there) is not big enough for the job really. I think I can get something that will do though.
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Old 16th Nov 2017, 8:27 pm   #6
Maarten
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Default Re: Philips N4510 reel motor

A BC640 is probably suited for the job, or you could try a BD140.
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Old 16th Nov 2017, 8:31 pm   #7
TonyDuell
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Default Re: Philips N4510 reel motor

The BC640 was what I thought of to, so I'll try that (when I've got a suitable tuit(circular) and ordered some) and let you know how I get on.
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Old 22nd Nov 2017, 9:33 am   #8
TonyDuell
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Default Re: Philips N4510 reel motor

Just a heads-up. I got some BC640s yesterday and have now fitted 6 to the flip-flop boards in this machine. They seem to work fine, the solenoids pull in properly, the control logic does what it should, etc. I will probably change them in the N4450 as well.

All (!) that remains to sort out on the N4510 is the tape counter. The drive pulley has a crack in it, so I need to make a replacement.
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Old 25th Nov 2017, 5:16 pm   #9
TonyDuell
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Default Re: Philips N4510 reel motor

Now done. I made a new pulley from aluminium alloy rod, fitted it with a grub screw and put the machine together. Seems to work find now.

I've also put the BC640s in the N4450, they are ideal for that machine too.
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