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Tomom 29th December 2012 05:40 AM

Has someone had some experience with this old , but good sounding, player?

Service note says to look for the following (no disc in):

1. The optical pick-up move to outside and then move to inside.
2. Laser beam emits spreadingly.
3. The objective lens perform up-and-down three times.

I have 2. and 3. but not 1. But player starts to play, for about 50 seconds, but then jumps back for about 20 sec. and keep repeating it. Focus coil transistors are getting very hot; I replaced them with new (stronger BD139/140), still the same. Could it be shorted coil?

I would like to fix it if possible as I want to replace audio section with discrete op amps - the player itself does actually sound surprisingly good, and is good base for mods.

Mooly 29th December 2012 01:26 PM

It sounds more like a problem with the sled rather than focus. If your 1, 2 and 3 refer to service modes then again, the problem of item 1 seems to confirm sled issue.

What pickup and mechanism type is used in this player ?

Have you checked to see the sled is free ?

Tomom 30th December 2012 04:20 AM

This morning I dismantled optical assembly - took sliding bars out, cleaned them and bushes. Lubricated with a bit of fine machine oil (didn't have white silicone grease but may get it later) and put it back together. Sled seam to be free and easy moving when pushing worm gear by finger. Still, transistors (focus coil) are getting hot again and it would jump back a bit after about 60 sec. of playing. I measured coils (focus and tracking), they are about 7 Ohms each - seams about right to me...

The pick-up mechanism is KSS-152A .

Mooly 30th December 2012 07:14 AM

Hard to say. I wouldn't expect the focus amp to very hot yet it doesn't sound like a focus problem.

Its worth connecting your meter across the sled motor and watch the voltage in play mode. The sled motor should have minimal voltage across it as the sled inches along. Perhaps as low as a few 10's/100's of millivolts.If the voltage starts to suddenly rise it indicates a problem with friction. When the voltage and motor power overcomes the friction the sled jerks causing the jumping.

Worth checking if only to eliminate it.

Tomom 30th December 2012 07:56 AM

Ok, I did what you said; initially voltage was around 20mV. As CD start playing, voltage started rising - it vent up to 4V in about 30 sec. and it stopped rising there, but CD kept playing for another 20 sec. or so and then jumped back.

I will open it up again. Interesting problem, as it did feel free to move when I was moving it by hand (finger)...

Mooly 30th December 2012 09:10 AM

Check the gears for burrs and for "tropicalised" grease (grease thats gone hard and "sugary). Also of course the sled motor could be faulty. Many sleds will often run end to end with just the "power" and voltage a DVM can provide on its diode range (just) but it give an idea of how it should be. Try a 1.5 battery and series resistor to whizz it up and down.

If the motor is suspect/faulty then discconect it (electrically and the gears) and apply 9 volts each way to see if it frees it up and cleans the commutator.

Tomom 31st December 2012 02:29 AM

I checked motor as per your suggestion - it would not run on DWM power, but did run happily on 1.5V and 9V...

Gears were all clean, and then I inspected bushes again, they are holes cut in plastic. To the naked eye everything seamed to be ok and clean. Then I used 10x magnifying glass and then I saw them: tiny layers, scattered here and there on the walls of bushes, of "tropicalised" grease. So I used suitable size drill bit and gently passed it through the holes few times and that cleared them. I assembled everything back together, using a bit of lithium grease, turned it on - and it works.

Though transistors on focus coil are still getting hot (PNP one more than NPN ?). That, I think , is just a design problem ( or a feature of the design). I will install small heat sink on them, just to help them out a little bit.

Thanks Mooly, and Happy New Year; and to every one else too...

Mooly 31st December 2012 06:28 AM

Excellent work, pleased to hear you were able to fix it. Can't say for sure without seeing the circuit but remember the focus drive transistors and coil are often just like a speaker coil and amp on a split supply, The focus coil has to be driven "upward" (the equivalent of a DC offset) and that means one transistor in the pair is doing more work and will get hotter. I'm sure its normal and OK.

Tomom 31st December 2012 11:40 AM

1 Attachment(s)
I have attached diagram with 8 transistors shown, just to confirm. I think it is the same problem as used to be with first generation of Sony CDPs, like 101 and 501...Their original driver STK6922 was getting terribly hot in operation driving focus coil, and would not last long. But that one could have been directly replaced it with Sony BX1201 and it was running cool. But I do not know what made the difference between two...

Mooly 31st December 2012 01:15 PM

In your circuit one transistor (say the NPN) is conducting to put (say) 1 volt DC across the focus coil so the transistor heats up. That means the PNP is non conducting so runs cold. However in practice the PNP acts as an active "pull down" on the coil although its work is minimal because the coil needs a positive voltage to bias it mechanically away from the rest position. So the heating of just one device is normal.

The BX1201 was a metal encapsulated package. I seem to remember there were some other components R's and C's to change the value of too.

But yours is fine :)

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