Luxman D-225 optical pick-up replacement - Page 2

anatech · 22nd November 2005, 02:39 PM

Hi Chicco,
I don't have that one, sorry.

What I want you to do is put the probe on the RF test point. Settings are 0.5uS / div (or as high as you can go) and 0.5V/div. use a 10:1 probe. You will see an RF waveform called an "eye pattern". What you normally would do is adjust the focus bias for the highest amplitude and sharpest pattern. Do not move any control very much. The next adjustments can get you into trouble easily. They are tracking offset and E-F balance. Do not touch without the service manual.

Send a picture of the RF test point before you do anything. It can be hard to catch. Also, try to measure (DC volts, 2-10 V scale) across a normally 22 R resistor near the RF amp that goes to the flat cable for the pickup head. Calculate the current. Compare to the Iop figure normally printed on the head. I use a laser power meter for quick checks, but they are expensive and I don't know what the expected value is for that head.

-Chris

anatech · 22nd November 2005, 02:43 PM

I see the heads are available from MAT electronics for $25. Here is a link to the page, it's down a fair bit.

-Chris

chicco_36 · 23rd November 2005, 01:16 AM

Hi Chris,
I spoke with my friend, he have hand made probe with 50 Ohm cable and termination on both ends of the cable with 50 Ohm resistors. Scope has 1Mohm/30pF input. Is it good at all?
In my first inspection I didn’t find adjusting pots, and without schematic I will have hard time to find measuring points and right values.
Thursday I will have more time to examine this problematic CDP and I will post new info.
Chicco

anatech · 23rd November 2005, 03:10 AM

Hi Chicco,
Sadly, that probe is exactly what you do not want in this application. What is required is a low capacitance 10:1 probe. 10Mohm input impedance (DC). This is the most common probe supplied with an oscilloscope. Common specs are 50 MHz or 100MHz bandwidth for the probe. Really old probes were speced at 10 MHz.

To use an oscilloscope for servicing, this is what you need to get a hold of.

-Chris

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22nd November 2005, 02:39 PM	#11
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Chicco, I don't have that one, sorry. What I want you to do is put the probe on the RF test point. Settings are 0.5uS / div (or as high as you can go) and 0.5V/div. use a 10:1 probe. You will see an RF waveform called an "eye pattern". What you normally would do is adjust the focus bias for the highest amplitude and sharpest pattern. Do not move any control very much. The next adjustments can get you into trouble easily. They are tracking offset and E-F balance. Do not touch without the service manual. Send a picture of the RF test point before you do anything. It can be hard to catch. Also, try to measure (DC volts, 2-10 V scale) across a normally 22 R resistor near the RF amp that goes to the flat cable for the pickup head. Calculate the current. Compare to the Iop figure normally printed on the head. I use a laser power meter for quick checks, but they are expensive and I don't know what the expected value is for that head. -Chris

22nd November 2005, 02:43 PM	#12
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	I see the heads are available from MAT electronics for $25. Here is a link to the page, it's down a fair bit. -Chris

23rd November 2005, 01:16 AM	#13
chicco_36 diyAudio Member Join Date: Sep 2004 Location: Skopje, Macedonia	Hi Chris, I spoke with my friend, he have hand made probe with 50 Ohm cable and termination on both ends of the cable with 50 Ohm resistors. Scope has 1Mohm/30pF input. Is it good at all? In my first inspection I didn’t find adjusting pots, and without schematic I will have hard time to find measuring points and right values. Thursday I will have more time to examine this problematic CDP and I will post new info. Chicco

23rd November 2005, 03:10 AM	#14
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Chicco, Sadly, that probe is exactly what you do not want in this application. What is required is a low capacitance 10:1 probe. 10Mohm input impedance (DC). This is the most common probe supplied with an oscilloscope. Common specs are 50 MHz or 100MHz bandwidth for the probe. Really old probes were speced at 10 MHz. To use an oscilloscope for servicing, this is what you need to get a hold of. -Chris

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