Philips CD834 (CDM-4/19) behaves strange, need help please - diyAudio
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Old 27th March 2014, 08:19 AM   #1
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Default Philips CD834 (CDM-4/19) behaves strange, need help please

I currently have this old Philips CD834 on the bench and it behaves like the laser is dead. But only up to a point, then it comes back to life...

Here's a typical scenario:
* Put in a disc
* Press play.
Disc will spin up for 2-3 seconds, then stop and display "No Disc"
Repeat this step about 25 times.
Now the disc spins more like 6-7 seconds before stopping, twice in a row.
* Press play again, now it spins for half a minute and then starts playing.
I let it run for about a minute, then
* Press stop, Open the tray and close it directly afterwards.
Display says "Reading", then "Disc Ready".
* Press play,
disc will start spinning counter-clockwise for some seconds, then display "No Disc" and then "Ready".
This repeats for another two times
* Press play again and now it will run fine!
I can stop and skip and change the discs just like with any working player, everything works fine now. I can even knock on the bench and it won't even start skipping like newer players with a weak laser.

Hope this makes sense to you .
So I was thinking that this might be due to some caps, because the player obviously needed some warm-up time. I replaced the biggest caps in the PSU, leaving all the smaller, sub-100uF ones in place, but to no extend. The problem still persists.

Now here's one more strange thing:
I let the player run through a whole disc for an hour, then let it "cool down" for 15 minutes, but WITHOUT turning it off! So it was just sitting there, waiting for me to press play again. And so I did:

* Press play,
display says "Play", disc spins for 2 seconds then stops, still displaying "Play"
Repeat this for 2 times
* Press play,
disc spins for about 6 seconds, then displays "No Disc" and then "Ready"
* Press play,
display says "Play", disc spins for 2 seconds then stops, still displaying "Play"
Repeat this for another 4 times
* Now everything will work again

So it's not the player itself that has to become "warm", but more the transport itself that has to do some work before it will actually keep doing so.

Any idea what this may be ?
I've read somewhere that this is caused by a faulty laser, but I've never seen one behaving like this. Usually they're bad right away and not becoming better after a while...

Any hints and tips are greatly appreciated !
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Old 27th March 2014, 09:04 AM   #2
esgigt is offline esgigt  Netherlands
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Hi, Lasse. Have you already downloaded a service manual ?

Cheers.
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Old 27th March 2014, 09:20 AM   #3
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Sometimes it is a lazy diode in the laser or spindle motor will not turn fast enough. On the odd occasion I have had to replace the small electrolytics on the control/FM board.
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Old 27th March 2014, 09:21 AM   #4
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Yes, I have. Unfortunately I don't have the test disc it mentions. I did check the values from chapter "laser current adjustment" with an ordinary disc though, and they were fine.
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Old 27th March 2014, 09:39 AM   #5
esgigt is offline esgigt  Netherlands
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Quote:
Originally Posted by JonSnell Electronic View Post
Replace the CD Mech. cdm4-19 | eBay
Sometimes it is a lazy diode in the laser or spindle motor will not turn fast enough. On the odd occasion I have had to replace the small electrolytics on the control/FM board.
If the laser is the culprit, replacing the unit could be the only solution.... From what i've read abouf similar problems, a faulty capacitor could also be the cause.

The data on the cd has difficulty to reach the players logic. A common cause is that the signal of the laser is not processed correctly due to this faulty cap. I'll try to find the sm myself and lookup which cap... get back later on this

Last edited by esgigt; 27th March 2014 at 09:48 AM.
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Old 27th March 2014, 09:48 AM   #6
esgigt is offline esgigt  Netherlands
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Quote:
Originally Posted by JonSnell Electronic View Post
Replace the CD Mech. cdm4-19 | eBay
Sometimes it is a lazy diode in the laser or spindle motor will not turn fast enough. On the odd occasion I have had to replace the small electrolytics on the control/FM board.
If the laser is the culprit, replacing the unit could be the only solution.... From what i've read abouf similar problems, a faulty capacitor could also be the cause.
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Old 27th March 2014, 01:53 PM   #7
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Thank you for your tips!

I've had a closer look at the schematic and replaced the four caps that were closest to the laser/servo circuitry, namely 2521, 2532, 2610 and 2622. Now the player starts up immediately, but it is extremely susceptible to even the slightest knock on the bench - it simply stops playback. There's no trying to re-focus like I know it from other devices. Looks pretty much like a dead laser now, if you ask me .
I'll let it run for a while and see how it behaves when warmed up again.
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Old 28th March 2014, 04:49 PM   #8
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Does not make a difference .
Guess I'll have to get a new unit soon, then. Well, at least it is working right after turning it on now, so thanks again for heading me in the right direction!
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Old 28th August 2014, 07:29 PM   #9
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Default Disc spins but stops without reading.

Quote:
Originally Posted by esgigt View Post
If the laser is the culprit, replacing the unit could be the only solution.... From what i've read abouf similar problems, a faulty capacitor could also be the cause.
I've changed the 4 caps listed and the cdm-4 unit. Problem still persists. Any suggestions would be appreciated.
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