help with magnavox cdb 650 please!

Discussion in 'Digital Sources' started by bobbyonions, Jan 13, 2011.

  1. bobbyonions

    bobbyonions AK Member

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    Hi all, I'm looking for some help here. I've had this older magnavox cdb650 (same as philips cd650) cd player for a couple years now. The cd player did not work when I got it, and was shelved for a couple weeks. Then one day I powered it up to tinker with it, and all of the sudden it was working. I listened to it for a couple weeks until it spopped working again. Last night I got it back out and popped the hood, fiddled with the tray and transport and it started to work and is working now. I don't now what I did to make it work or if it just coincidentally started working on it's own.
    I've read good things about this cd player and it's mod potential which is the reason I'd like to hang on to it and get it working. I was looking at the large board under there and noticed some solder blobs that look like someone was up to something. The PO was an electrical engineer and audiophile , so it wouldn't surprise me if he repaired or modded this unit. I'm attaching some pics hoping someone can tell me what they think.
    As far as symptoms, when the player works, it works 100%. When it doesn't work, the motor and spindle just spins away as long as the unit is powered up. If you load a cd, it will go in and spin, but the player will not recognize it and shows some sort of error on the display. If you eject the cd it comes out spinning full speed in the tray.
    If anyone can guide me through some troubleshooting, I'd really appreciate it. I know my way somewhat around vintage tube gear, but cd players are absolutely foreign to me. Thanks.
     

    Attached Files:

  2. dr*audio

    dr*audio Fish fingers and custard! Subscriber

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    The solder blobs are from the factory. Normal for that unit. 2 things seem to be happening;
    1. Intermittent disc motor servo operation.
    2. Possible read failure from the CDM unit.
    I replace a lot of CDM units on these players. It is possible it is going bad. The only way you can troubleshoot this is with an oscilloscope. You will also need the service manual. This will tell you how to access the service mode and tell you the test point locations and how to adjust it. It is possible an adjustment is out of range.
     
  3. Grainger49

    Grainger49 Old Fart

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    This is the CDP that started all the tweaking. A number of "High End" CDPs of the day were 650s with a new face plate and a tubed output stage. So lots of folks saw potential in them.

    Old CDPs I have seen have often had the problem you describe. The laser sled is not reading the TOC (Table Of Contents) and therefore is not recognizing the disk although it knows that there is a disk there. It keeps trying to read and just spins. Probably the designer didn't put in a time out for this function.

    I have lubricated the rails that the sled rides on to help, but not permanently cure, that problem. If you check with MCM Electronics they might have an NOS replacement for the sled/mechanism.

    If you get or can point me to a schematic I can suggest some component upgrades if you like. I might even have an article on this one somewhere in my audio files.
     
  4. bobbyonions

    bobbyonions AK Member

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    Thanks for that info. That seems to stop me dead in my tracks, because I do not have an oscilloscope. Assuming that your rough diagnosis is accurate, what should a repair like that run?
     
  5. Dr Tinear

    Dr Tinear AK Subscriber Subscriber

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    The Magnavoxes of that era all used swing-arm CD mechanisms. There are no sled rails to gum up.

    A common failure on the CDM-2/10 disc drive in the CDB-460, 560 and 650 is a 33 uF axial-lead electrolytic capacitor on the servo board. It's part of the power supply for the laser diode. If this capacitor loses value or goes open, the symptoms will resemble a dead or dying laser diode. Change the capacitor and don't touch the potentiometer that's near it on the board. The laser diodes don't often fail on these drives.

    You should also check to make sure that the swing arm moves freely over its entire arc, without any hitches in its motion. The laser head flex circuit shares a routing channel with the swing arm counterweight. If the clip that retains the flex circuit works loose, the flex circuit can rub against the counterweight and cause skips, seek errors and even failures to read the TOC.

    Finally, check the laser lens to ensure that it moves freely in the focus voice coil. The first CDB-650 I ever worked on had similar symptoms to yours, all of them caused by a piece of dirt in the focus voice coil gap. A careful cleaning with compressed air cured the problem.
     
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  6. bobbyonions

    bobbyonions AK Member

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    Thanks for that info. Those are some things I CAN check.
     
  7. bobbyonions

    bobbyonions AK Member

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    Finally, check the laser lens to ensure that it moves freely in the focus voice coil. The first CDB-650 I ever worked on had similar symptoms to yours, all of them caused by a piece of dirt in the focus voice coil gap. A careful cleaning with compressed air cured the problem.[/QUOTE]

    What's the procedure for checking the movement on this mechanism? Thanks alot!!

    On a side note. I've been listening to this all morning A/B up against a TDK da-5900 cd player/recorder. I've been syncing up the same cd in both units and switching back and forth on my preamp selector. I was expecting to hear a clear difference in sound quality. I read how nice these philips players with the tda1541 are supposed to sound. Honestly, I'm wondering what all the fuss is about. If anything, I can hear a slightly fuller sound in the magnavox, particularly in the bass, but nothing that a half-notch turn on my preamps tone wouldn't accomplish. Am I missing something? Maybe the TDK is pretty good too? Maybe my system isn't detailed or resolved enough to hear the difference? Any thoughts on that end anyone? Maybe I should start a new thread on the sound quality issue.
     
  8. Dr Tinear

    Dr Tinear AK Subscriber Subscriber

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    I pushed on it very gently with a Q-tip. If it moves easily and returns to center when you remove the swab, it's probably OK.

    The '650 is a good player in stock form, but needs a few parts transplants to reveal the full excellence of its DAC. The NE5532 or LM833 op amps in the analog filter are too slow to follow the waveforms at their inputs without slew-limiting. On my '650, I removed the op amps, installed 8-pin sockets at the two chip locations, filled the sockets with Analog Devices AD827 dual op amps, and beefed up the op amp power supplies. The player sounded much smoother and more natural in the highs when the job was completed.
     
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  9. bobbyonions

    bobbyonions AK Member

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    I checked the laser lens (held by thin flexible spring steel?) I pushed on it with a q-tip and it seems to be free moving.
    I'm definately interested. I just have no idea of the real life hearable potential, so I'm hoping if I got into fixing/modding that I would feel it was worth it sound wise.
    It's worth it for me pretty much to jump in just because I like learning and tinkering with this stuff and I like the unit in terms of build quality and the kind of old school looks and layout. It doesn't have quite the disposable feel of most stuff off the shelves these days. I'm going to look into the upgrades that you mentioned. If you have more detailed info for me that you have time to share that would be great.
    I was looking at the servo board (underneath the drive assembly?). What's the proper way to disassemble things to access that board? Thanks.
     
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  10. jhoyt

    jhoyt Incomprehensible space llama

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    Four Torx T10 screws will let the servo board come off. BE CAREFUL about the flex ribbon cable, it must not get damaged.

    Also, there is a "NOS Mod", or Non-Over Sampling. It is supposed to take the sound to a new level, along with replacing opamps and capacitors with modern units. If I can get mine fixed, I'll be trying these mods.

    Good luck!
     
  11. dr*audio

    dr*audio Fish fingers and custard! Subscriber

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    You absolutely must use anti-static protection when you disconnect / connect the flat flexible cable going to the laser assembly, and put a paper clip on the end of the cable to short out the contacts when it isn't connected to the board. The lasers in these players are very susceptible to static damage. Wear an antistatic wrist strap, grounded to a cold water pipe when you work on it.
     
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  12. Dr Tinear

    Dr Tinear AK Subscriber Subscriber

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    My advice on the NOS mod can be summed up in three words: DON'T DO IT.

    The technically-ignorant folks who recommend this mod apparently don't realize or care that removing the digital filter without installing a brick-wall analog filter as a replacement will leave you with a player that puts out very high levels of ultrasonic noise along with the audible signal. This noise can drive your downstream preamp and amp into gross nonlinearity if they're not band-limited at their inputs (and very few are). It can also let the magic smoke out of your tweeter voice coils. The NOS advocates may like the sound of grossly-distorting gain stages and expiring tweeters. I don't, it isn't music.
     
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  13. bobbyonions

    bobbyonions AK Member

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    Thanks for that info. Is there a cheapo way to make an ant-static set up with common household/shop items?

    Thanks for the advice. The unit is still working. Would a bad cap on the servo board cause it to work intermittantly, or just not work at all? I'm planning on replacing that 33uf cap regardless, but I'm trying to see if that is likely the problem.
    As far as the op amps, do you recommend a seller for the sockets and op amps? I see they are available on bay. Are they all the same? I notice some have different suffixes. Anything I should watch out for? As far as upgrading the power supply, is there a procedure and parts list available anywhere? I located a schematic on hifi engine, but it is not in English.
    I stated earlier that this didn't sound a whole lot different than my tdk cd recorder. I A/B it against a denon player I have and the magnavox completely blew it away.
     
  14. dr*audio

    dr*audio Fish fingers and custard! Subscriber

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    Wrap a wire around your wrist and tie the other end to a cold water pipe. NOTE: this method will tie your body directly to ground, and would be dangerous if you touch any live electrical circuit, so don't work on the unit while it's powered up while you have this ground wire on you. If you want to make a safe ground, go to Radio Shack and buy a 4.7 Meg Ohm resistor, and put it in series with the ground wire to limit the current. A real wrist strap and static mat already have this resistor inside.
    MCM Electronics sell inexpensive anti static wrist straps and mats.
     
  15. bobbyonions

    bobbyonions AK Member

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    Thanks. Done.

    OK, I'm becoming comfortable enough under the hood to be dangerous. The focus voice coil is good, the clip on the ribbon cable is secure and swing arm swings freely. I've located the 33uf 16V axial lytic on the servo board. Not sold locally, so I will have to order that.
    The motor makes a distinct whirling noise when disc is spinning. Is it normal to hear this noise? It's quiet enough that I could think it is normal. The noise does have a pulse sound per revolution too. I've ruled out the top pressure plate or hub as a source of the noise.
     
  16. dr*audio

    dr*audio Fish fingers and custard! Subscriber

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    The noise is normal. Digikey will have the cap. I am sure there are other things you could use from them, such as solder wick to remove the cap with, and the electrolytic caps.
     
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  17. bobbyonions

    bobbyonions AK Member

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    Thanks dr*audio. Yeah, I think it's time for a new iron too. Mine works fine for point to point stuff, but a more delicate clean tipped one is in order. This will be my first time on a circuit board.
    What other caps would be suspect for failure or prime locations for upgrades? I am interested in upgrading the op amps and power supplies as mention by dr tinear.
    What's the proper way to dress connections? I have deoxit, but I don't want to go spraying that anywhere it doesn't belong.
    It looks like there is a little lithium lube on the tray rails. Is that factory applied? Should I lube anything mechanical under there?
    I really appreciate the coaching. Thanks.
     
  18. dr*audio

    dr*audio Fish fingers and custard! Subscriber

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    I would replace the main supply filter caps. Basically replace any large caps on the board. Also get yourself some 8 pin dip sockets and install them in place of the opamps so you can easily swap out opamps to try others.
    The lithium lube is factory, and a good idea to clean it off and re-lube.
    I would not buy a soldering iron from Digikey. I recommend the Hakko 936, from these people:
    http://www.tequipment.net/Hakko936-12.html?gclid=CLXC3N2tvaYCFUS8KgodrDurIQ
    They have the best price, and their service is excellent. I am very happy with mine.
     
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  19. jhoyt

    jhoyt Incomprehensible space llama

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    Hey, thanks for this information. I had only heard the "pro" side, and not any of the drawbacks. Do you think the TDA1541 with oversampling is still deserving of its reputation, or can better be readily found?
     
  20. bobbyonions

    bobbyonions AK Member

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    I like the sound of the mod you have done, but I can't find a manual in English, and I don't know if I could follow it if I had one. Could you describe in more detail which ps caps should be upgraded with the AD827 op amp transplant? Also will any AD827 do?
     

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