Nakamichi MB-75 e-disc error - Page 2 - diyAudio
Go Back   Home > Forums > General Interest > Car Audio

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 28th December 2012, 07:36 PM   #11
frobek is offline frobek  Poland
diyAudio Member
 
Join Date: Dec 2012
Location: Poland
Laser diode is connected to collector of the PNP transistor. I measured voltage on emitters resistor (10 Ohm) and it was 0,41V, so Emitter current was ca. 40mA (Ic+Ib).
  Reply With Quote
Old 28th December 2012, 07:49 PM   #12
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Normally you measure the volt drop across the resistor to get the current. The laser should only be "lit" for the brief moment that the focus search operation is being performed. After that it is turned off. A typical laser current is in the 50ma region but its very device dependent and unless you have the exact value the individual pickup was calibrated at then the measured value can only be a rough guide that the laser is at least drawing somewhere in the expected current range. In full size players many pickups have the value incorporated as part of the pickup serial number for reference.

For general info...

If you take a laser diode and gradually increase the current from zero then it functions first as a side emitting red LED. There is no laser action. As the current increases more and more then suddenly lasing begins and the optical output increases dramatically. From this point a tiny further increase in current causes a massive increase in the optical output. Go a bit to high and the laser is damaged or destroyed. Its a fine window of operating current that is needed and is why the laser diode has an integral photodiode to monitor the "optical" output and maintain the "optical" output at an exact level. The current varies according to temperature and also as the laser ages. The laser power control circuit always tries to maintain the optical power at a constant level by altering the current but this current is always within a fairly narrow window.
__________________
-------------------------------------------------------
Installing and using LTspice. From beginner to advanced.
  Reply With Quote
Old 28th December 2012, 08:43 PM   #13
frobek is offline frobek  Poland
diyAudio Member
 
Join Date: Dec 2012
Location: Poland
The volt drop I measured across the resistor is changing during focusing procedure.
  Reply With Quote
Old 29th December 2012, 04:30 PM   #14
frobek is offline frobek  Poland
diyAudio Member
 
Join Date: Dec 2012
Location: Poland
After a couple hours of checking the problem I am almost sure that the laser is broken. And now the question is, if it's possible to buy a KSS-602A pickup laser, or somehow repair it?
  Reply With Quote
Old 29th December 2012, 04:59 PM   #15
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
If all checks point to the laser then it its time to look at replacement. I couldn't turn anything up on the KSS 602.

Have you checked to make sure that the spindle motor servo output and motor drive really is "non functional". We're assuming the pickup isn't focusing and that the system control isn't getting the Fok (focus OK) signal.

Its worth looking at the problem from another angle.
__________________
-------------------------------------------------------
Installing and using LTspice. From beginner to advanced.
  Reply With Quote
Old 29th December 2012, 06:25 PM   #16
frobek is offline frobek  Poland
diyAudio Member
 
Join Date: Dec 2012
Location: Poland
During focusing:
I cheked RF amplifier output with oscilloscope - no signal.
On the photodiode output (that one to control laser output power) : voltage level ca. 200mV, change to zero when trying to focus, not always, 1 of 5.
Another possibility is RF amplifier CXA2521 damage.
I didn't check RF amplifier input due to lack of space. I have to solder some wires to connect the oscilloscope.
What do you think I am supposed to check more.
  Reply With Quote
Old 29th December 2012, 07:03 PM   #17
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
All I could think of was to check the spindle motor drive amp during focus search. That would be just to confirm that the motor isn't spining up purely because there really is no spindle drive output from the servo. Very unlikely the problem would be there but it just covers all bases before deciding the pickup is faulty. Any measurements would have to be done during the brief focus search time.

And never overlook supplies. Are they all correct and not low. Once you've done all that then the pickup is the most likely suspect.
__________________
-------------------------------------------------------
Installing and using LTspice. From beginner to advanced.
  Reply With Quote
Old 29th December 2012, 08:01 PM   #18
frobek is offline frobek  Poland
diyAudio Member
 
Join Date: Dec 2012
Location: Poland
I checked spindle motor driver out. - no signal. Power is ok.
  Reply With Quote
Old 29th December 2012, 08:40 PM   #19
diyAudio Member
 
freax's Avatar
 
Join Date: Sep 2007
I once span a sony playstation playing a music cd by hand, it worked and gave an audio output.

I'm thinking that If you can spin it fairly fast it might lock on, if its that then you know where the problem is.
__________________
"It seems that perfection is reached not when there is nothing left to add, but when there is nothing left to take away" - Antoine de Saint Exupéry
  Reply With Quote
Old 29th December 2012, 09:18 PM   #20
diyAudio Member
 
Zero Cool's Avatar
 
Join Date: Sep 2004
Location: MN
welcome to the wonderful world of Nak car stereo's....I gave up on them! the cd-changers always had problems!
__________________
It's not about what you can BUY...It's about what you can BUILD!
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
nakamichi mb-2 disc loading problem deafdumband50 Digital Source 6 16th June 2013 08:37 AM
nakamichi MB-75 george21 Car Audio 2 1st December 2010 04:25 AM
nakamichi mb 75 wesley64 Car Audio 0 2nd January 2010 07:48 PM
Nakamichi MB-75 CD has no sound white93nsx Car Audio 1 18th July 2009 12:56 AM
Nakamichi MB - 75 AUX Input aladdin_s Car Audio 0 15th September 2008 11:02 AM


New To Site? Need Help?

All times are GMT. The time now is 10:39 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2