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Old 16th Feb 2018, 5:24 pm   #1
emeritus
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Default Philips N2501 cassette deck

This 40-odd year old deck stopped working due to loss of teeth from the idler gear that drives the take-up hub. Fortunately I had invested in a copy of the official Philips service manual for this machine shortly after buying it. As removing the failed gear required almost complete dismantling of the mechanics, its description of how to disassemble it was invaluable, as were the many write-on plastic bags in which I put the numerous springs, circlips and sets of screws that had to be removed in the procedure, numbered as per the exploded diagram.

Fortunately there were enough teeth remaining on opposite sides to measure the diameter and determine the number of teeth. A post on this forum produced an offer of a reduction gear with the same large diameter, pitch, thickness, and bore, and it was only necessary to remove part of the smaller gear to match the axial length of the original idler. As the cut surface would be the lower surface and functioning as a bearing, it needed to be smooth and square. Not having a lathe, I came up with the idea of using a 2mm bolt to mount it in the chuck of my ancient 12V EXPO minidrill, clamped in its drill stand laid on its back, and to temporarily fix some washers over that part of the small gear that was to remain, to prevent too much material from being removed. Three thin brass M5 washers were about right, and I glued them together and to the gear using some of my last remaining tube of genuine "Cow Gum". It was then simple to set the drill running and make the cut using an X-Acto-type razor saw, gently biassing the blade against the end brass washer while moving the blade to and fro. I continued until it was almost through to the bolt and then removed the gear and finished sawing by hand. My calculations had been correct, the axial thickness matched, the cut surface was smooth and square, and it was then a question of putting it all back together again. The metal circlip that retains the pinch roller assembly on a plastic shaft had been the devil to remove and in the end had broken, but there was enough of it left to work. One of my late mother's small metal crochet hooks was useful in pulling various springs from the depths to engage various lugs on reassembly: with hindsight it would have been easier and quicker to have put some loops of nylon cord in the end loops of the springs and use them to pull the springs up.

As the manual identified where and with what to lubricate, I cleaned and re-lubricated everything before reassembling. The specified Shell grease was long discontinued, but it turned out to be a standard automotive wheel bearing lithium grease. The specified oil was ordinary W20-50 engine oil. Rather than dismantling the capstan assembly to oil it, I applied traces of oil at its exposed ends using the nib of an old fashioned steel pen.

Reassembling the mechanics into the case looked daunting as you have to line up lugs on the piano keys with the actuating shafts on the deck, likewise for several switches when refitting the printed circuit. However, once aligned the circuit board just dropped into place without problems, and a replacement drive belt from CPC finished it off.

In this model, the motor drives the capstan all the time that power is switched on. The bore of the replacement gear turned out to be slightly off-centre, so its eccentricity produces a faint rhythmical noise when no keys are pressed. As it is permanently engaged with a metal gear on the capstan shaft, it might bed itself in with use.

In practice, the slight gear eccentricity has no discernible effect in performance. The noise reduces to an almost inaudible level when PLAY is selected and the idler engages the take-up hub. Violins sound like violins rather than wailing cats! It rather shows up the flutter levels of the music centres that I recently got going by fitting new drive belts: I think their pinch rollers may need replacing as they are rather shiny as they now don't like the C120s that make up the bulk of my cassette collection that they used to have no problems with.

Thanks again to Ambientnoise for sending me the gear FOC so promptly in response to my post on another thread, much appreciated.
Attached Files
File Type: pdf 1- Damaged gear.pdf (556.7 KB, 72 views)
File Type: pdf 2- Cutting to size .pdf (974.1 KB, 53 views)
File Type: pdf 3 - Reassembly .pdf (1.11 MB, 62 views)
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Old 17th Feb 2018, 5:15 pm   #2
Ambientnoise
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Default Re: Philips N2501 cassette deck

Good work and write-up. I did one a couple of years ago but luckily the replacement gear went straight in. They must have used different materials originally as just the one had "rotted".

Ken
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Old 20th Feb 2018, 3:13 pm   #3
Phil G4SPZ
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Default Re: Philips N2501 cassette deck

Great story! I still like and use cassettes, so it's nice to read about a machine being given a new lease of life.
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