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Old 20th March 2013, 07:31 PM   #1
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Default Magnavox CDB-473 squeals when powered on

Years ago I bought a Magnavox CDB-473 but stopped using it when it seemed like the laser was going bad, replacing it with a somewhat inferior (but cheaper) Philips 920. Recently I got it out of the basement and on a whim fired it up. It seemed to play flawlessly. The only problem was a squealing noise when powered on. I removed the cover and noticed that when turned on with a disc in it, the disc would move a little and stop, there would be a squeal, then the disk would start spinning again then stop after the disc info was read. There's a power-on squeal with or without a disc. As I am a newby to all of this, I would appreciate some ideas as to what to check out before I disassemble it and then realize that I have no idea what I'm doing.
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Old 21st March 2013, 06:11 PM   #2
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Service manual for Philips CD473 is available free but can't remember where from. Maybe in German or Dutch but the diagrams are useful, and detail the CDM mechanism and loader.

CDM2 or early CDM4 with a top plate made out of beautiful heavy plastic that doesn't ring, but to screws it's like a mixture of chalk and soap. Remove screws carefully and slowly, and do not overtighten.

It has the later polystyrene loader without a mechanical brake. That eliminates one possible cause.

Most obvious culprit would be the spindle that spins the disc. If the disc seems stiff to spin, the spindle may be sticking. This is annoyingly inaccessible, but an aerosol tube just about wiggles in under the bit the disc sits on. The kind of light silicone grease that comes in an aerosol can is safe to use but be careful none gets on the lens. If any normal oil or grease has been used in the past it should be thoroughly removed because it makes the plastic sticky. Wipe away surplus grease carefully and make sure none will spin out onto the laser head. This can be done without taking anything to bits.

Second obvious cause is the disc is rubbing on something. Check it isn't.

It's possible that the disc isn't gripped well enough, but that doesn't usually make it squeal. The bit the disc rests on should be clean, as should be the disc itself. The top clamp should be free to move easily in any direction, and spin, of course.

The bottom bearing of the Hall effect spindle motor is not adjustable and requires some disassembly to access. If you've greased the spindle as above, then surplus grease will have dripped into the bearing so it should be OK. If it seems stiff and needs taking apart be careful not to overtighten the screws when you reassemble.

Use the right size torx driver bits, please.

Squealing can be caused by an oscillating motor driver, with the focus or tracking motor acting like a speaker. Check mechanical causes first.
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Old 21st March 2013, 06:33 PM   #3
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Quote:
Originally Posted by PlasticIsGood View Post
Second obvious cause is the disc is rubbing on something. Check it isn't.

It's possible that the disc isn't gripped well enough, but that doesn't usually make it squeal. The bit the disc rests on should be clean, as should be the disc itself. The top clamp should be free to move easily in any direction, and spin, of course.
Thank you for your response. It likely isn't the case of the disc rubbing or being inadequately gripped, as there's squealing on power-on even when there's no disc loaded. It stops after a couple of seconds.

I found the Philips CD-473 manual in Dutch. From what I understand, that player was identical to the Magnavox CDB-473.
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Old 21st March 2013, 08:51 PM   #4
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I think on power-on it gives the spindle a little spin but I'm not sure. It moves the head to where a TOC might be and tries to focus. So it could be any of these things. If it only squeals when starting with a stationary spindle, and steps through tracks without squealing, then I would suspect the spindle, its motor (unlikely), or the circuit that drives it. If it doesn't try to spin on power-on, then it must be either the swing-arm or focus motor. The arm is heavy so is more likely to hum than squeal. The focus motor is very light.

If it only squeals from standstill, then it could be because it is finding it hard to find and settle on the focal point. There are any number of reasons why that could be, unfortunately. What's more, unless your model is blessed with a removable bottom panel, it's maddeningly hard to position the mech so it will run without blocking access to the circuit that runs it. A voltmeter across each motor would tell you which is associated with the noise, probably. Scope would be better. The big problem is access.

Best bet initially is to hope someone recognises this particular squealing.

The player has a test mode that allows you to step through several stages of the process of reading a disc. This involves holding two keys down on power-on, but I can't remember which...should be decipherable in the manual even if you don't read Dutch.
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Old 21st March 2013, 09:23 PM   #5
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By the way IIRC, the 473 has a volume control circuit with no bypass. I think it sounds good as it is but if you are inclined to change opamps, a user-selectable bypass, or alternative output sockets, would be an early requirement of any improvements.

Worth saving anyway. Most parts can still be found.
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