Help with cdm-1 MK2

[zenleung]

Hi all,
I got my Krell trasport pre-owned and recently replace the laser due to not disk reading problem. After tunning the laser offset and beam current it fast read all disks without problem.

After 1-2 days running now problem exists, I smell bad burning from it after power on, I discovered 1 burned 1 ohm resisitor on the servo PCB after opened it up (see the picture). I replaced it with a new one the machine work perfectly again but the bad burning smell coming from the same resistor location after I power on the machine without playing disk. 1 side of the resistor with extremely high temperature when I touch it. Please have you kind advise what is the possible cause of problem and how to fix it?

Many thx in advance

[stephensank]

THE FIRST THING you need to do is replace that blue electrolytic capacitor, the one with 2103 beside it, with a new Nichicon(axial or radial matters not), then re-install the OLD CDM unit to see if the resistor still overheats. No doubt, AT ALL, the blue cap is the reason your old cdm stopped working. I've never, ever seen a CDM1-mkII have any problem other than this one cap failing. If the resistor stops burning with the old mech, then there is a fault in the new one.

[tiefbassuebertr]

Originally Posted by stephensank

THE FIRST THING you need to do is replace that blue electrolytic capacitor, the one with 2103 beside it, with a new Nichicon(axial or radial matters not), then re-install the OLD CDM unit to see if the resistor still overheats. No doubt, AT ALL, the blue cap is the reason your old cdm stopped working. I've never, ever seen a CDM1-mkII have any problem other than this one cap failing. If the resistor stops burning with the old mech, then there is a fault in the new one.

This is right.
goes from PIN 17, TDA5708 to GND (unbuffered out of APC for Laserdiode, goes to the base of buffer transistor, also PIN17 by TDA8808, but here not "C 2103")
http://www.datasheetcatalog.org/data.../499947_DS.pdf
I use still a 63V version for the electrolytic and add a MKT cap for bypass the electrolytic (0,47uF - 2uF) .

[poynton]

Originally Posted by stephensank

................I've never, ever seen a CDM1-mkII have any problem other than this one cap failing...........

Neither have I !!!!!

I wonder how many good drives have been thrown away because of those blue caps?

I'm a bit concerned the OP adjusted the laser current ... How?



Andy


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[stephensank]

Originally Posted by poynton

Neither have I !!!!!

I wonder how many good drives have been thrown away because of those blue caps?

I'm a bit concerned the OP adjusted the laser current ... How?



Andy


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I suspect that a shocking number of CDM's have been tossed in the trash due to ignorance of this cap. Since I have been working on, e.g., Revox A77's since the ate 70's, I knew of the poor durability of German brands of electrolytic caps(forgive this generalisation, but I doubt anyone can argue this point that has long experience), so I had little troube identifying the fault the first time I had read problems with a player thus equipped. The voltage rating of that cap need not be increased. If you use a Nichicon or at least a Nippon Chemicon, even a 16V cap will last forever.

There is a fairly easy procedure for adjusting laser current, which actually had you measuring the current drain of the PD array, rather than actual LD current. However, to get it right with CDM-0-through-4 units, you have to do the adjustment with a BROAD range of cd's, and go for best range compromise window of +/-5mv of the 50mV spec. Using one disc will have it reading only have the cd's in your collection, usually.

[tiefbassuebertr]

Originally Posted by stephensank

I suspect that a shocking number of CDM's have been tossed in the trash due to ignorance of this cap. Since I have been working on, e.g., Revox A77's since the ate 70's, I knew of the poor durability of German brands of electrolytic caps (forgive this generalisation, but I doubt anyone can argue this point that has long experience), so I had little troube identifying the fault the first time I had read problems with a player thus equipped. The voltage rating of that cap need not be increased. If you use a Nichicon or at least a Nippon Chemicon, even a 16V cap will last forever.

There is a fairly easy procedure for adjusting laser current, which actually had you measuring the current drain of the PD array, rather than actual LD current. However, to get it right with CDM-0-through-4 units, you have to do the adjustment with a BROAD range of cd's, and go for best range compromise window of +/-5mv of the 50mV spec. Using one disc will have it reading only have the cd's in your collection, usually.

This mentioned blue axial cap isn't from German brand. As I know, it is a Dutch brand (Philips, formerly VALVO), but I doubt, even this. Only the labeling is from there and the real manufacturer certainly anywhere in far east; outsorcing (certain work areas) is the keyword.
The really only bad electrolytic cap from Germany I know are the red plastic caps from Roederstein (ROE), often used by Krell and Mark Levinson - go to
http://www.soundparts.jp/capacitors/...0/roe22-40.jpg
Krell SBP-64X - YouTube
The yellow FRAKO axial caps (often to find by Revox and Braun) mostly in good condition, even after 40 years (unfortunately not the radial outlines).
http://www.elektroda.pl/rtvforum/fil...estaw_1427.jpg

[zenleung]

Originally Posted by stephensank

THE FIRST THING you need to do is replace that blue electrolytic capacitor, the one with 2103 beside it, with a new Nichicon(axial or radial matters not), then re-install the OLD CDM unit to see if the resistor still overheats. No doubt, AT ALL, the blue cap is the reason your old cdm stopped working. I've never, ever seen a CDM1-mkII have any problem other than this one cap failing. If the resistor stops burning with the old mech, then there is a fault in the new one.

Stephen,
Thanks very much for your advise and I had replaced the small blue "Philips" axial cap as recommended (I did replaced all the other electrolytic caps except this one and the disk reading problem already improved a lot). After I re-stall everything I finally discovered the problem of overheating the resistor is caused by earthing the servo PCB to ground (1 of the fixing screws that connecting the PCB to the CDM-1 aluminum chasis ground the PCB to the CD player casing via the spring isolator of the CDM-1!
Now the laser pickup read all discs strong!

[zenleung]

Originally Posted by tiefbassuebertr

This mentioned blue axial cap isn't from German brand. As I know, it is a Dutch brand (Philips, formerly VALVO), but I doubt, even this. Only the labeling is from there and the real manufacturer certainly anywhere in far east; outsorcing (certain work areas) is the keyword.
The really only bad electrolytic cap from Germany I know are the red plastic caps from Roederstein (ROE), often used by Krell and Mark Levinson - go to
http://www.soundparts.jp/capacitors/...0/roe22-40.jpg
Krell SBP-64X - YouTube
The yellow FRAKO axial caps (often to find by Revox and Braun) mostly in good condition, even after 40 years (unfortunately not the radial outlines).
http://www.elektroda.pl/rtvforum/fil...estaw_1427.jpg

That's true it is a "Philips" cap but not German brand.

And sad to hear that the ROE cap have leak problem! I owned quite a lot of gears with these caps (Krell, Audiolabor)!

[stephensank]

I believe the blue cap is a relabeled Siemens, a brand I have found extremely unreliable. In my experience, the worst reliability among European lytics is from Frako(ask any Revox tech), followed by Roederstein(as you say), followed by Philips, Siemens, and can't recall the others at the moment. But most of these are not as guaranteed to be bad after 10 years as Elna, Panasonic/Matsushita & Rubycon. Even worse, by far, is Nover, but I don't know where those are made. But, essentially, 30+ years of pro service work has proven to me that the only lytic brand that is virtually never the source of problems is Nichicon, followed not far behind by Nippon Chemicon. Only time I see Nichicons fail is from lightning damage or caps that were run more than 50% over voltage rating for some years(as in the case with a large number of Audio Alchemy DDS Pro transport units). One more generalisation- Any lytics that are epoxy sealed, such as the red/brown Roe's and one line of Chemicons used by Levinson/Cello, where there is no way for the cap to "out-gas", will ALWAYS start leaking after a few years. So, if it's got an epoxy end seal, REPLACE IT.

[poynton]

Originally Posted by zenleung

...............Thanks very much for your advise and I had replaced the small blue "Philips" axial cap as recommended .................

Does your original CDM-1 work now ??


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