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NEC CD-730 with a finicky laser
NEC CD-730 with a finicky laser
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Old 12th April 2019, 02:36 PM   #1
einzelherz is offline einzelherz  United States
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Default NEC CD-730 with a finicky laser

I recently picked up a dirty, but good condition NEC CD-730. It does not play discs (and the drawer is misbehaving but I think I have that sorted). It has the same KSS-150A as my Sony CDP-207ESD so I've been using that one to try and diagnose this NEC.

Upon putting a disc in, the spindle motor will spin it about the same amount as the Sony to read the track listing but [DISC] keeps flashing on the display while the laser constantly raises and lowers. The laser continues to do this after the disc stops spinning at least once more (with a faint but familiar click when it drops). On occasion the spindle motor will spin the disc backwards too, but I'm not really sure what that's about.

The laser sled seems to work okay - I've manually retracted it and when loading a disc it will return to its home position fine.

My current guess is that the laser itself is weak. Letting both the NEC and Sony load no disc with a white reflector above the laser, the Sony appears to be significantly brighter.

Would this behavior be in line with a laser that's weak and can't get a focus on the disc?

Thanks in advance!
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Old 12th April 2019, 04:29 PM   #2
mlloyd1 is offline mlloyd1  United States
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Location: Northern Iliinois
NEC CD-730 with a finicky laser
this site has been very helpful to me over the years for maintenance and repair of my cd players:
Notes on the Troubleshooting and Repair of Compact Disc Players and CDROM Drives

mlloyd1
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Old 15th April 2019, 01:30 PM   #3
einzelherz is offline einzelherz  United States
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Thanks for the link!

Oddly enough a second pass of cleaning with some isopropyl (door stop switch, both parts of the laser, the grounding pad on the laser) and it's functional now. I'm getting static during songs on some CDs (mostly newer pressings or CD-rs) so I think I'll need to focus its laser.
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Old 25th April 2019, 08:14 PM   #4
einzelherz is offline einzelherz  United States
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Finally hooked an oscilloscope up to it and while it was pretty well focused, the laser in it (and my 207ESD) seem tired. Their eye/RF measures are about .8-.9v on the scope but ~.2v lower using my multimeter. I assume that's because it's an erratic DC current and my multimeter is doing some averaging.
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Old 20th May 2019, 08:00 PM   #5
einzelherz is offline einzelherz  United States
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Replaced the lasers and went through the service manual tuning all of the calibration settings (E-F, eye, bias, focus, etc). Oddly, there is still one CD I have that it just HATES reading. It's picking up a lot of errors (they come over like popping on vinyl) and it shows up over digital out or going through the TDAs.

At this point I just assume it's just having difficulty with the bitstream on this one disc? Maybe it has something to due with the inverting and balancing compared to a single chip player?
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