Hello,
I am looking for advice on how to troubleshoot a Nakamichi CD Player 4 that quit working suddenly. It does not read the CD. Here is some preliminary testing that I have done. Not sure where to go from here.
Opened the unit and found that on power up the laser carriage moves to the forward position and trips the leaf switch (checked OK) and then stops. Usually in most other CD players that I have seen, the carriage first moves to the extreme forward position, trips the switch and then moves back and forth before it settles down. In my case the back and forth movement is not observed after the initial forward move.
The laser is working and the lens moves up and down. I have checked all clocks, voltages and the related transistor voltages as shown in the schematic. All look good. The only concern that I have is that the VCO output from the Sony CXA1082BS is not 8.64Mhz. It is 10.5Mhz. Adjusting VR105 to one extreme end only brings the frequency down to 9.5Mhz. Not sure if this is the problem and what is the fix. I would like to be sure it is indeed CXA1082BS that is defective before changing it.
Any help or advice will be greatly appreciated.
Regards,
Veej
I am looking for advice on how to troubleshoot a Nakamichi CD Player 4 that quit working suddenly. It does not read the CD. Here is some preliminary testing that I have done. Not sure where to go from here.
Opened the unit and found that on power up the laser carriage moves to the forward position and trips the leaf switch (checked OK) and then stops. Usually in most other CD players that I have seen, the carriage first moves to the extreme forward position, trips the switch and then moves back and forth before it settles down. In my case the back and forth movement is not observed after the initial forward move.
The laser is working and the lens moves up and down. I have checked all clocks, voltages and the related transistor voltages as shown in the schematic. All look good. The only concern that I have is that the VCO output from the Sony CXA1082BS is not 8.64Mhz. It is 10.5Mhz. Adjusting VR105 to one extreme end only brings the frequency down to 9.5Mhz. Not sure if this is the problem and what is the fix. I would like to be sure it is indeed CXA1082BS that is defective before changing it.
Any help or advice will be greatly appreciated.
Regards,
Veej
How have you adjusted the VXO ? Typically you need a low capacitance probe to prevent the measuring equipment affecting the frequency.
Its not impossible for there to be a problem with the VXO but its unlikely. Try coupling the probe via a really small cap (like 2.2pf or 4.7pf) and recheck the result.
On further probing, it seems that the VCO may not be the problem given the fact that the o'scope probe might be loading it as Mooly rightly pointed out. The 3.5V output for the VCO is good too. What I have noticed is that once the CD carriage closes without a CD, the lens jumps up right away and immediately drops down. At this time the laser is still on and remains so for about 5 seconds and then shuts off. I assume that the lens should try to focus by moving up and down and then lock. Am I wrong in this assumption?
The lens tries to focus on the stationary disc. If that happens then the "Fok" or focus OK line changes logic state and tells the system control to spin the disc up to approximately the correct speed... from then on the servo takes over and the speed is adjusted so that the data rate coming off the disc is locked to the main crystal oscillator. The free running speed of the VXO needs to be within this "pull in" window or else the servo will never operate. Having altered that you now have a double problem of the original fault and one you have introduced.
The VCO is exactly at the same frequency as it was originally. I have measured the frequency as well as measured the POT voltages and set it to what it was before I trimmed it.
Taking your explanation into consideration, I probed the FOK pin. When the carriage is in the out position, the voltage is 0.101V. After a disc is loaded and as long as the laser is on, the voltage is 0.010V. Once the laser shuts off, it reverts to 0.101V. Obviously this is not a logic change. Moreover, when probed on a scope, this line is very noisy. Does this imply that the laser unit is not functioning?
Taking your explanation into consideration, I probed the FOK pin. When the carriage is in the out position, the voltage is 0.101V. After a disc is loaded and as long as the laser is on, the voltage is 0.010V. Once the laser shuts off, it reverts to 0.101V. Obviously this is not a logic change. Moreover, when probed on a scope, this line is very noisy. Does this imply that the laser unit is not functioning?
I wouldn't have thought it should noisy, so that might point to a pickup issue. With it just sat there I would say the FOK line should be clean. It should also be clean with no disc inserted and the laser doing its search routine.
Have you scoped the rails, particularly the supply to the pickup/laser diode driver. Typically that would be one of the main 5 volt rails.
Have you scoped the rails, particularly the supply to the pickup/laser diode driver. Typically that would be one of the main 5 volt rails.
All supplies are clean. 5V supply is measured as 5.03V and at the pickup it is measured as 4.93V.
I also found that per schematics, voltage at base of Q108 (NPN) and Q109 (PNP) should be 0.3V. However, I read -0.3V. The base of these two transistors are connected to SPDLO (disc motor amp output) pin of CXA1082BS and the emitters are connected to the disc motor and SPDL- (non inverting input to disc motor amp) pin The emitters are always sitting at 0V. But after insertion of disc, the disc motor spins for a second. At this time the voltage is 0.7V and then goes back to 0V. My suspicion is that one or both of these transistors could be bad.
Voltages for other driver transistors connected to CXA1082BS read correctly as shown in the schematic.
I also found that per schematics, voltage at base of Q108 (NPN) and Q109 (PNP) should be 0.3V. However, I read -0.3V. The base of these two transistors are connected to SPDLO (disc motor amp output) pin of CXA1082BS and the emitters are connected to the disc motor and SPDL- (non inverting input to disc motor amp) pin The emitters are always sitting at 0V. But after insertion of disc, the disc motor spins for a second. At this time the voltage is 0.7V and then goes back to 0V. My suspicion is that one or both of these transistors could be bad.
Voltages for other driver transistors connected to CXA1082BS read correctly as shown in the schematic.
I wouldn't be so sure they are faulty tbh. If the disc spins briefly then that suggests focus has been found. What you need to look at if you can is the RF signal from the disc during that brief spin up period. Look at the amplitude and general "quality" of the signal. If the amplitude is low (pickup problem) then the servo won't lock. When you earlier said the FOK line was noisy, was that during the spin up of the disc. If so then a low amplitude signal could explain that (as it causes severe dropouts).
Amplitude of the RF is typically around 1.2 to 1.5v pk pk for many players.
Amplitude of the RF is typically around 1.2 to 1.5v pk pk for many players.
Probing RFI pin of U101, I see a clean sine wave that is 2.58V p-p and ~1.2Mhz. The schematic shows an image of a series of sine waves in succession. I have not bee able to capture this on the scope. It is always a single sine wave.
Probing RF- pin of U101, I see a sine wave that is 220mV and ~1.2Mhz.
Probing EFM pin of U101, I see a square wave that is 2.4V p-p.
Probing FOK pin of U101, I see a noisy dc signal that is sitting at about 50mV. It does not change state even when the disc motor turns on for a second.
I also noticed that if I look at the lens from an angle, it does move up and down as if trying to focus after the CD carriage moves in. First it pops up to the max upward direction, then drops down and then moves up and down ever so slightly. After about 5 seconds, it drops down and the laser shuts off. During this whole process, FOK line does not change state at all.
Probing the focus coil of the pickup directly, as long as the focusing is operating the output signal resembles a capacitor charging and discharging. It is a -2.2Vp-p.
Probing RF- pin of U101, I see a sine wave that is 220mV and ~1.2Mhz.
Probing EFM pin of U101, I see a square wave that is 2.4V p-p.
Probing FOK pin of U101, I see a noisy dc signal that is sitting at about 50mV. It does not change state even when the disc motor turns on for a second.
I also noticed that if I look at the lens from an angle, it does move up and down as if trying to focus after the CD carriage moves in. First it pops up to the max upward direction, then drops down and then moves up and down ever so slightly. After about 5 seconds, it drops down and the laser shuts off. During this whole process, FOK line does not change state at all.
Probing the focus coil of the pickup directly, as long as the focusing is operating the output signal resembles a capacitor charging and discharging. It is a -2.2Vp-p.
I found out that the sine wave that I was observing on RFI pin was actually being picked up by the o'scops probe. C102 are wires for the photo detector. If the probe is resting on C102 wires, the signal is there. But once the probe is moved away from the wires it disappears. So basically, there is no eye patterns that I can observe on the RFI and RFO pins.
The RF signal for a normal spinning disc (servo locked) will look like these (various images in post #1). The RF is identical for ANY music CD. If the disc speed is incorrect, which it will be if it just spins up and slows back down again then the frequencyof the signal will contract and expand along the X axis. The amplitude would be constant. If the servo is not locked (yours wont be) then the diamond pattern will be very very poor and noisy, again the amplitude should be correct.
So it does seem a little at this stage that there could be a problem with the pickup.
http://www.diyaudio.com/forums/digital-source/226288-sony-cdp790-kss240-restoration-project.html
So it does seem a little at this stage that there could be a problem with the pickup.
http://www.diyaudio.com/forums/digital-source/226288-sony-cdp790-kss240-restoration-project.html
Hello,
I received the KSS-150 pickup yesterday. I have installed it but not powered it up since I am not sure if there is a solder short or a capacitor that I need to remove. I believe I had read about this some time in the past. I do not see any short but I do see a capacitor on the pickup pcb that has the two connectors and the pot. Just want to make sure before I move ahead.
I received the KSS-150 pickup yesterday. I have installed it but not powered it up since I am not sure if there is a solder short or a capacitor that I need to remove. I believe I had read about this some time in the past. I do not see any short but I do see a capacitor on the pickup pcb that has the two connectors and the pot. Just want to make sure before I move ahead.
Well, after power up the results are the same as well as I do not see a laser. With the previous laser unit, I could see the laser quite faintly. I say faintly because I opened another Sony DVD player and observed that on loading a empty tray, the laser turns on and is quite bright. The laser carriage also moves back and forth and then stops when it does not detect a CD. None of this is happening in the Nakamichi. I also do not see the diamond signal (eye pattern) on pin 1 of U101.
I do not have any specific experience with this Nakamichi model but from what you describe I think your laser pickup and transport are healthy. It seems that the logical sequence stops when the laser discovers the CD and has to read out the TOC. This is where the clock comes in. It is possible that the crystal is drifting or overtoning or that adjacent loading capacitors are leaking.
Try leaving the CD on for 15 minutes and see if it works then. Another favourite way of testing a potentially faulty crystal is to pinch it with two fingers without touching the chassis and pressing play while holding the crystal.
EDIT: if the new transport behaves differently that may be due to the fact that you did not remove the protection short circuit from the laser diode. Also, there will be no eye pattern before the CD player enters PLAY.
Try leaving the CD on for 15 minutes and see if it works then. Another favourite way of testing a potentially faulty crystal is to pinch it with two fingers without touching the chassis and pressing play while holding the crystal.
EDIT: if the new transport behaves differently that may be due to the fact that you did not remove the protection short circuit from the laser diode. Also, there will be no eye pattern before the CD player enters PLAY.
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