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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 5th Aug 2017, 6:07 pm   #1
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Default Philips F880 Music Centre Cassette Decks.

The cassette decks in this music centre weren't working mechanically and an investigation showed that the drive belts had changed to the usual goo which I removed.

I'm now fitting new belts from one of those Chinese packs of assorted belts. The question is how should the belts be routed? A belt from the motor to each capstan pulley (behind the aluminium flywheels), then a belt form there to the associated spool drive pulley? Or a belt from the motor to each spool drive pulley, then a belt to the associated capstan? The pulleys all have two grooves, so there's no clue there and some grooves are clearly redundant. Don't take any notice of the belts in the picture, that's just me experimenting.

The decks run at constant speed, but are slow. Is there any electrical adjustment? The motor has four wires going to it.

Thanks.
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Old 5th Aug 2017, 8:28 pm   #2
ms660
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Default Re: Philips F880 Music Centre Cassette Decks.

Do the flywheels have a groove?

Lawrence.

Last edited by ms660; 5th Aug 2017 at 8:33 pm. Reason: Re wrote
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Old 5th Aug 2017, 10:55 pm   #3
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Default Re: Philips F880 Music Centre Cassette Decks.

There are no grooves in the flywheels.

I managed to work out the belt routings by trial and a lot of error. The motor pulley has two grooves and, as it's very small, the belts need to be in contact with a large part of its circumference. So no belts going round three pulleys.

A belt from the motor to the right hand capstan pulley would foul the spool drive pulley, so the initial drive is from the motor to the spool drive pulleys and the secondary drive is from the spool drive pulleys to the capstans. Then there's the question of whether the belts goes in the inside or outside groove of the pulleys. Get that wrong and the belts rub on the chassis.

I found a pot which adjusts the motor speed and set it as close as I could by ear.

Problem now is that the two decks run at slightly different speeds. This could be down to belt slip, but it's more likely due to my having to use belts of slightly different cross sections from the motor to the spool drive pulleys. I guess the larger cross section belt sits further out in the grooves.
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Old 9th Aug 2017, 10:13 am   #4
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Default Re: Philips F880 Music Centre Cassette Decks.

After some experimentation I arrived at the belt arrangement shown in the picture.

The right hand deck has to be belted as shown, as attempting to drive the capstan pulley directly from the motor results in the belt fouling the spool drive pulley.

The left hand deck could have been belted in a similar manner to the right hand deck, but the arrangement shown means that only two sizes of belt are required rather than three.

I traced the slowness of the left hand deck to the tape counter drive belt, which was not changed, having slipped off its pulley causing drag. This pulley is hidden in the picture, but is actually part of the spool the tape is wound from during record and play operations.

The hole giving access to the speed change pot is shown with a red square around it. It is adjusted using a hex key.

I made a test cassette on a better quality machine by recording a 3kHz tone on both tracks. The tone was supplied by an AF generator with a frequency counter being used to accurately set the frequency at 3kHz.

The tape was then played back on the F880 and the counter was used to check the frequency at the loudspeaker. The pot was then adjusted to give 3kHz. It turned out that my "by ear" setting was quite a way out.
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Old 9th Aug 2017, 10:53 am   #5
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Default Re: Philips F880 Music Centre Cassette Decks.

For anyone without a frequency counter, here is how to set the speed without one. Generate some tone on a computer (I used 1kHz) and save it to a file. Use the file to burn an audio CD. Record the CD to a cassette using a known good deck. Playback the cassette on the deck to be adjusted while playing the CD (a ghettoblaster is good enough for this). Adjust the cassette speed so that the tones merge and there is the smallest possible beat (the cassette speed is unlikely to be stable enough for a consistent zero beat).
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