Hi fellow LD enthusiasts

I came across this information today which explains how to correctly identify the illusive "NULL POINT" when calibrating a Laser optical block "grating". I followed it today when calibrating my CLD-1750 and it works like a charm

The grating is a specialised lens in the optical block that splits the main laser in to 3 discrete beams. Two for driving the tracking circuits and one for data retrieval. If it's not set correctly then some discs will read and other older discs will not. Older discs tend to be more fussy about how they are read/played back. Maybe the tracks have shrunk over the years who knows! I would be very interested to compare my Pioneer calibration disk with my older "fussy discs". Either way if your laser does not tack properly then you are out of luck and your player will eventually reject the disc.

You do need an oscilloscope to check for the tracking signal.

I've included some pictures of an old optical block I have so the curious amongst you don't have to take your player to pieces! - Anyway this is like my 3rd post here so I do hope that you all enjoy.



The laser grating slot for calibration. Laserdiode can be seen to the left (solderjoints).


Grating and prism for splitting the beam.


Grating and Laserdiode (rear, solder joints)


Laser Optics/beam splitter and lens that directs the information from the LD back to photosensitive components to generate the EFM signal for decoding.

Where's that description from? Doesn't look like a Pioneer doc...

ARP2000 Adjustments for CD Players Vol. 1

Rarely do I touch grating when servicing a working player. I insert the test disc and make sure centering, focus, and tracking are good. I check frames 115, 475 etc for crosstalk and adjust based on that. Does this sound about right?

Pioneer covers this adjustment in the newer pickups so you cannot adjust it. The older Pioneer players did perform this step, I believe the CLD-D702 family was the last to have access.

Yes from what I have read the grating is only accessible on older Pioneer LDs, newer ones it's factory sealed... It's tricky to find the laser null point so I thought I would make this post to assist others.

I have another recent issue with rectifying AC to DC. Would this be of interest to this community?

F#475 amongst others is a great way to test for inter channel interference or crosstalk... The sharp edges of the black bar against a white background make it easier to check for inter channel interference.