Help With Faulty Philips CD850 MkII

[Rbz5416]

My poor old CD850 MkII has been languishing in the loft for the last ten years after developing a fault. I've never been able to bring myself to bin it but have finally decided something must be done. I'd dearly love to bring it back to life so wondered in anyone had an idea regarding the fault?

What happens is that a newly inserted disc starts to spin but before it reads the contents, the disc motor stops & then starts spinning backwards!

I've had it apart as far as I dare but cant see how to remove the carrier for the laser assembly. The laser/motor sits in a floating plastic chassis & is held with four torx screws. Removing these frees the laser/motor but the ribbon cable is obstructed by the floating chassis. This seems to be held in position under the main chassis by plastic lugs & I can't see any way to free them.

Oh, & for good measure the tray gear disintegrated. I know these were available on Ebay but obviously need to solve the main problem first. Otherwise I'll just stick in on Ebay for spares/repair as it has the original user manual & remote.

[Rbz5416]

Well, while waiting for the post to be approved, I remembered that buried in the bowels of the garage was an old Philips external CD-ROM drive of similar vintage. That couldn't possibly also have a CDM4/19 mech, could it?

So I dug it out & pulled the lid of to reveal - a CDM4/55. No Idea what the /19 & /55 variants signify but the mechs looked identical apart from the motor connector only having three pins instead of four, but then only two are used. So I swapped everything over but the tray gear spindle broke. But it left a small hole behind so I managed to slip a tiny screw in there for now.

Powered up & it works! Well, nearly. The sound is very thin & vocals are almost inaudible so I guess I need to make some adjustments to the laser. I've found a PDF copy of the service manual so will go & study that, but it's not a great scan. If anyone has a quick guide to any adjustments I need to make I'd be very grateful.

[JonHarrison]

If it tracks ok why do you think the laser needs adjusting ?

I'd check the power supply voltages and ripple and perhaps look to replace the capacitors.

[awpagan]

It might be just dirt/dusk on the lens of the laser

On the original mechanism...
clean the laser with a dry cotton bud and see what happens first

Allan

ps I do have the PDF service manual for the CD850II
PM me if needed

[Rbz5416]

Originally Posted by JonHarrison

If it tracks ok why do you think the laser needs adjusting?

It doesn't track OK, just the first few tracks.

But the good news is I had tested it using headphones & I've just discovered that the cable going into the phones themselves had pulled slightly out. The sound from the 850 is fine!

So having scrutinised the service manual with a magnifying glass, I've managed to locate the two points were the measurements are made for adjustment of the laser. Just need to find the time to solder some wires to them & make the adjustments as my multimeter doesn't have any croc clips.

The temporary bodge on the tray gear has already failed so I'll look at gluing a pin through it or just order a replacement from Ebay.

Originally Posted by awpagan

It might be just dirt/dusk on the lens of the laser

On the original mechanism...
clean the laser with a dry cotton bud and see what happens first

Allan

ps I do have the PDF service manual for the CD850II
PM me if needed

I cleaned the laser when it failed ten years ago, it appears that it had failed completely. No idea why that would cause the disc motor to spin backwards though!

Thanks for the offer of the PDF but I already have it thanks.


The tricky decision will be parting with it when/if it's sorted, but they seem to be fetching £150 on Ebay & I no longer use a CDP.

[fastvideo]

check if there are any short on the 2 motor drive transistors. Replace it if that is the case and clean the brushes of the motor and check the motor is not sucking excessive current before power up.