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Old 19th September 2012, 05:04 PM   #1
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Default philips cdm 4/21 & 4/25

Hello I have just joined so hello DIY'ers

I have a question. Does anyone know the differences between the philips cdm 4/21 and 4/25??.

Thank you

Chris
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Old 19th September 2012, 09:36 PM   #2
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The 25 is common, and the 21 is rare

The only 21 I've seen is on ebay just now, although it says that the label has been overwritten 29, which AFAIK doesn't exist. The seller has removed the picture of the underside, so I've attached it below.

Pictures of the 25 are easy to find.

The obvious difference is the spindle drive. On this paltry evidence, the 21 has a commodity brushed motor rather than the Hall-effect drive of the 25.

However, I have an Aiwa with a 4/25 (I'm pretty sure), with a brushed motor
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Old 20th September 2012, 11:23 AM   #3
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mmmm interesting. thanks for that. Hopefully the laser unit is compatible between them!.
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Old 20th September 2012, 12:50 PM   #4
Mooly is offline Mooly  United Kingdom
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Although I can't recall specific model numbers there were a lot of differences between platter motors in early variants. Some used hall effect motors, some DC (as in picture) and even between the hall effect types there were major differences.
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Old 20th September 2012, 06:17 PM   #5
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Quote:
...Hopefully the laser unit is compatible between them!
This exquisitely ambiguous and ludicrously expensive offering says yes, and no, maybe, in two languages.

JusTone Lasereinheiten. CDM4/11 Ersatz Lasereinheit Laufwerk Lasereinheit, Laserpickup, Laserunit, Pickup, Laser, Laserkopf

The 21 and 25 are both listed in Philips manuals as replacement units for various CDM2 mechs, and appear to be compatible with the same servo board. However, there are several variations of radial motor circuit, and these are not necessarily reflected in the model numbers.

The laser itself is probably compatible, as long as you use the correct procedure for installing a new one. This appears to be the same for all models, and involves pre-adjustment before switching on, so make sure you follow a manual.

Last edited by PlasticIsGood; 20th September 2012 at 06:26 PM. Reason: took out "as Mooly says", because he didn't!
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Old 21st September 2012, 11:31 AM   #6
amc184 is offline amc184  New Zealand
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I've seen quite a few of the rarer CDM-4 variants, there's quite a lot of them. I don't have a list of the exact differences between each type, but these are the things that differ between them:
- Motor type, brushed or brushless
- Chassis type, miniature or table, different leg lengths
- Spindle type, clamped, magnetic, ball grip, spring grip, inverted
- RAFOC type, onboard or offboard laser power adjustment

With all those variations you can see why there are so many type numbers. The 4/11, 4/19 and 4/36 are common, but most of the rest are fairly rare, either being made as stopgap replacements for CDM2s or semi-custom items for low volume manufacturers like B&O.

You can generally swap the RAFOC (the swingarm with the laser head) between the different types, just keep a watch out for the rare types that had onboard laser adjustment potentiometers (like most Sony lasers). They were mainly fitted to jukeboxes, and have a potentiometer on the flex foil, like the picture attached. They aren't compatible with other types and vice versa.
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Old 24th September 2012, 10:43 AM   #7
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Long shot!! Has anyone got a 4/21 I could buy of you???? Prettyyyyyyyy please with a cherry on top?
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Old 3rd October 2012, 03:12 PM   #8
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still after a 4/21??. The laser section doesn't have to be working
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Old 3rd October 2012, 04:17 PM   #9
Mooly is offline Mooly  United Kingdom
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Why not ask here,
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