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Magnavox cdb560 hum +music at output

Discussion in 'Digital Sources' started by UncleBingo, Feb 13, 2018.

  1. UncleBingo

    UncleBingo AK Subscriber Subscriber

    Messages:
    990
    Howdy,
    Looking at this CD player for a friend. He said it was humming along with the music. (Perhaps it doesn't know the words?) Both channels.
    I don't usually work on these, but thinking it was possibly a bad ground on the output RCA's I agreed to crack it open and have a gander.
    Short story is that the hum is somewhere else. I've pulled and measured the power supply (filter caps) and they're within 20%. I even subbed in a couple new caps there to zero effect.
    Swapped out the LM op-amp chips and still... hum
    Lifted 1 leg of the main diodes and they test good.
    I am suspicious of the 78XX series regulators in here, but not crazy about going full rabbit-hole without some assistance (or at least a shove in a meaningful direction).
    Anyone conquer this hum on a similar unit? (Phillips/Magnavox).
    I have Multimeters, oscilloscopes and function generators available and probably a frequency counter somewhere. Thanks.
     

     

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  2. CT Jim

    CT Jim AK Subscriber Subscriber

    Messages:
    3,066
    Location:
    Branford, CT. 06405
    I have a cdb465 which suddenly developed some static during playback. I have not pulled anything yet, but will be watching this thread for additional tips for when I get it on the bench. I did find the Philips cd-465(same model) service manual, but I'm not impressed with it, I suppose I could just replace 20+ caps and hope that solves it?
    This model has a super motorized tray system, I'd like to get it back up and running.
     
    UncleBingo likes this.
  3. UncleBingo

    UncleBingo AK Subscriber Subscriber

    Messages:
    990
    Odd that nobody has had or fixed this problem on this or a related model. Anybody?
     
  4. markuus3889

    markuus3889 Diatom, what's that?

    Messages:
    307
    Hi UncleBingo,

    You may have better luck over at DIY audio. Search for "CDM2" info since that is the transport and some variation of "Philips CDM2" and/or your model. Quite a few units from Philips/Magnavox and other various manufacturers used the CDM2 and its variations. I think there are three variations of that type transport. There were known problems with electrolytic caps on the transport I think it was a 33uf but the blue electrolytic axial caps with thin blue shrink wrap are all problematic in those units. Though I don't know if that's your issue. There should be a lot to read. You should find manuals for the Philips CD560(same as Mag CDB560) and Philips CDM-2(under Philips General Documents) at Hifi Engine.

    Good luck,

    Mark K.
     
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  5. UncleBingo

    UncleBingo AK Subscriber Subscriber

    Messages:
    990
    Thanks! I have the manuals, but they're a little thin...
     
  6. onanysunday

    onanysunday AK Subscriber Subscriber

    Messages:
    481
    Location:
    Minneapolis
    I would try swapping out the op amps with an opamp socket and then plug-in some new op amps to see if this reduces extra noise in your audio signal. Use a small value film capacitor on the underside of the PCB to solder pin 4 to pin 8.
     

     

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  7. onanysunday

    onanysunday AK Subscriber Subscriber

    Messages:
    481
    Location:
    Minneapolis
    I assume you're listening through the rear RCA jacks? Make sure those are nice and polished on the inside and out. If your listening through a headphone jack (if it has one) I found those can introduce some noise into the audio path unless the headphone socket is cleaned out thoroughly rubbing alcohol, contact cleaner or Deoxit. Besides that just your usual contact cleaning, lubricating of the switches, checking grounds etc.
     
  8. UncleBingo

    UncleBingo AK Subscriber Subscriber

    Messages:
    990
    I did put sockets in and swapped the op-amps. I'll try the caps. Seems like too much noise to be that.
     
  9. UncleBingo

    UncleBingo AK Subscriber Subscriber

    Messages:
    990
    Noise is the same through headphones or RCA's. Grounds have been checked and soldered as well as all modular plugs cleaned.
    It almost sounds like motor hum bleeding into the signal chain somehow...
     
  10. UncleBingo

    UncleBingo AK Subscriber Subscriber

    Messages:
    990
    This isn't just extra noise, more aptly, mostly hum with some audio riding on top.
     

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