Troubleshooting CD Players

[dr*audio]

Greeting​

Thank you, Dr, for being a steadfast contributor to the resurrection of many a fine CD player. I've got a new one for you, if you please.

Context​

This Sony CDP-C35 is very susceptible to skipping from light taps on the table or from tonal vibrations. TOC loading, seeking, playing are good if not disturbed at all. Track seeking takes about 3 seconds. I've verified the top arm yoke is not contacting. I can wiggle it with the whole CD tray while playing and get no rubbing or skipping. Pickup springs have been re-stretched and suspension feels sturdy yet compliant. Lens looks clean. Spindle motor top bearing lubricated. All transport mechs clean and lubricated. I can hear a lil repeating noise from what I think is the tracking or focus motors, once per revolution of the CD. The motor itself seems quiet when it first spins up or down.

I'm very very new to using an oscilloscope so don't assume I'm measuring things correctly here. I totally understand that teaching OSC operations is outside the scope of this thread.

RF​

RF measurement looks messed up. Do I need to set a trigger mode on the OSC to properly see the diamond pattern or is this simply not right? There's nothing in the manual to suggest how to calibrate this.

View attachment 3312556

Focus​

I'm pretty sure I have focus set properly to ~100mV center. But, am seeing conflicting info in the svc manual.

View attachment 3312557

In the manual I see this
View attachment 3312576... and thisView attachment 3312578

First graph is centered on 100mV with a 200mV p-p. Second graph is centerd on 0V with a 500mV p-p? What is correct? Why are these different?

Tracking​

I don't think tracking is correct. The screenshot in the svc manual is hard to interpret. I think the manual wants to see a 2v p-p amplitude with a 0v center? Best I can get is about 700mV top to bottom.

View attachment 3312562

Again the two sections of the svc contradict each other (unless they mean different things I don't understand yet)
View attachment 3312579View attachment 3312580
My interpretation of the first image shows 0V center with ~2V p-p? Second graph shows 0V center with 100mV p-p?

Thanks​

Thank you for your time!

1. The rf; your scope needs to have the sweep set faster, maybe 2uS/div.
2. The focus is ok, I think.
3. The Tracking offset is adjusted with the tracking gain turned down, then you will see the 2V p-p waveform, and you quickly adjust for 0V offset (waveform symmetrical above and below 0.
The rhythmic ticking you hear is an important symptom. Look at the spinning Cd and see if it is eccentric or if the outer edge moves up and down. Could be the motor shaft is bent or there could be foreign material on the disc table.

 

[deckblad]

...

Thank you!

Isn't 200nS faster than 2uS? At no time window does the output appear stable or geometricly patterened like in the service manual. Could you point out or recommend any pots/adjustments that effect this output? Or, should I leave it alone?

Can you clarify my assumption that, as I'm accessing the focus and tracking pots from the underside, that clockwise is lower value and counterclockwise is higher?

I'd since found a value for tracking that gives me pretty solid playback now. So I may have lucked out! At this point I'm mostly interested to know about the RF calibration.

Thanks again!

 

[Ullar]

Before going further, this unit has a position locater, which is a variable resistor attached to the sled motor and moves with it. Try putting a bit of Deoxit on it and slide it back and forth a bunch of times. See if that helps. It's #12 in the picture below:

Thank you for your advice. I rubbed the position locator with some contact cleaner. It looks nice and even. No scratches or stains. Voltage on the connector is within limits (0.3 to about 4 V depending on the position of the pickup). Still the same symptoms.

Should I remove and test sled drive transistors? Or are there some other checks I could do before that??

 

[dr*audio]

Thank you for your advice. I rubbed the position locator with some contact cleaner. It looks nice and even. No scratches or stains. Voltage on the connector is within limits (0.3 to about 4 V depending on the position of the pickup). Still the same symptoms.

Should I remove and test sled drive transistors? Or are there some other checks I could do before that??

The sled drive comes from the tracking error. Once the tracking error gets above a certain amount, correction is applied to the sled drive. So we need to go back and look at the Tracking error signal, the output to the tracking coil, then the sled output. make sure the scope is DC coupled. We need to see if the output goes both positive and negative. If not, the output transistors are suspect.

 

[dr*audio]

Thank you!

Isn't 200nS faster than 2uS? At no time window does the output appear stable or geometricly patterened like in the service manual. Could you point out or recommend any pots/adjustments that effect this output? Or, should I leave it alone?

Can you clarify my assumption that, as I'm accessing the focus and tracking pots from the underside, that clockwise is lower value and counterclockwise is higher?

I'd since found a value for tracking that gives me pretty solid playback now. So I may have lucked out! At this point I'm mostly interested to know about the RF calibration.

Thanks again!

You're right; 200nS is .2uS. I couldn't tell where the setting was, it looked like it was too slow.
So now that it plays, have a look at the rf waveform again. Adjust the Focus offset for max waveform and read the p-p value.

 

[Ullar]

The sled drive comes from the tracking error. Once the tracking error gets above a certain amount, correction is applied to the sled drive. So we need to go back and look at the Tracking error signal, the output to the tracking coil, then the sled output. make sure the scope is DC coupled. We need to see if the output goes both positive and negative. If not, the output transistors are suspect.

Hello again!

1. Tracking error (pin 6 of Optical Servo Control IC) is about 0.4Vpp, and is centered at 0V.
2. Output to tracking coil (measured at emitters of output transistors Q161/162) is about 4Vpp, and is roughly centered on 0V.
3. Sled output (measured at emitters of output transistors Q181/182) is about 0.7Vpp and has a positive bias varying between 3v to 7V. It is jumping around quite a bit and is difficult to measure accurately but ha clear positive bias.
Tracking coil and TE signals are centered on 0V.

Can we make anything out of that?

 

[Bumpalump]

Since you have it where you can get it to play, connect your scope up to the RF test point and look at the eye pattern. If it's less than 1V P-P, the laser is bad. If it's less than 1.5V p-p, you can try adjusting the laser power to bring it up to 1.5V. Then play an entire CD, monitoring the RF test point. If it drops off, the laser is bad. On a customer unit, if the laser power is low I replace the laser.

Incrasing LD current is the worst advice, because it leads to an immediate shortening of life.

If the RF signal amplitude is not within spec the first thing is to clean the external collimator, if its not enough you have to clean in a bit deeper, internal collimator, prisms etc

RF signal decrasing is only by the dust on optical parts, never by the diode itself so the current should be left alone once its set in factory, excep that you can measure the current draw by LD and compare it to the current pointed on last 3 digital of serial number, also measure the optical power which is different on the optical pickup but for most of the sony pickup is about 90-110uW

 

[bangsezmax]

So Liberty electronics on ebay sells good lasers that they source in China. I've used them, they seem to last and work well. I had one dud and they replaced it immediately. I wouldn't buy from anyone else.

Back to my problematic Nakamichi CD Player 4 -- I've replaced the laser with one from Liberty and I'm not out of the woods yet.

Yesterday after replacing the laser, I was getting intermittent loading. I thought maybe it was a platter motor-related issue, so I removed the PCB and sprayed a small squirt of DeOxit into the hole at the bottom of the motor. This seemed to help -- I was able to get it to load almost every time and it worked all day. I though I had it licked.

Then this morning, it's back to it not loading most of the time. I get the feeling that if I mess with it long enough -- loading, unloading, trying to get to TOC -- it will eventually work again. But then if I turn it off and let it sit for a few hours, I'll back to square one -- it won't load, or will load very intermittently.

So my conclusion, having ruled out the laser, is that it's likely an issue with the motor -- it's just wonky and needs to get warm to function normally. But it also could theoretically be whatever electronic component (IC?) controls the motor. Same idea -- could be a cold solder joint that warms up or the component itself is failing. The other possibility -- or possibly an additional factor, and this is just a hunch based on the behavior when I try to get it loading again -- something to do with the table height. This is because sometimes messing with the position of the top bracket seems to have a positive effect on the loading behavior. Of course, that may not have anything at all to do with it. This is why intermittent faults are so maddening -- you can't be sure if something you did to change the environment had an effect vs random behavior patterns.

By now I've spent so much time on it -- and a new laser -- that I'm going to be extremely frustrated if I can't solve the puzzle. I'm open to any guidance at this point.

Edit: one more interesting behavior that may or may not be relevant -- sometimes when ejecting the disc, the disc motor will spin backwards (counterclockwise). Not always, just sometimes.

 

[Ullar]

The sled drive comes from the tracking error. Once the tracking error gets above a certain amount, correction is applied to the sled drive. So we need to go back and look at the Tracking error signal, the output to the tracking coil, then the sled output. make sure the scope is DC coupled. We need to see if the output goes both positive and negative. If not, the output transistors are suspect.

Hello again!

1. Tracking error (pin 6 of Optical Servo Control IC) is about 0.4Vpp, and is centered at 0V.
2. Output to tracking coil (measured at emitters of output transistors Q161/162) is about 4Vpp, and is roughly centered on 0V.
3. Sled output (measured at emitters of output transistors Q181/182) is about 0.7Vpp and has a positive bias varying between 3v to 7V. It is jumping around quite a bit and is difficult to measure accurately but ha clear positive bias.
Tracking coil and TE signals are centered on 0V.

Can we make anything out of that?

Investigated a little further but still confused. dr*audio, your input would be greatly appreciated.

With no disc in player, sled coil voltage is 0.1V (Vpp 0V) as it should be according to manual. I couldn't resist and pulled sled signal output transistors but no problem there. Both of them in working order (hfe 165 and 153).
I still can't identify where the source of my problem lays. Could it be somewhere in sled drive circuitry? There is an IC with 4 op amps and one, strange to me, (switching?) IC.
Here is the video of sled coil signal:

 

[dr*audio]

Investigated a little further but still confused. dr*audio, your input would be greatly appreciated.

With no disc in player, sled coil voltage is 0.1V (Vpp 0V) as it should be according to manual. I couldn't resist and pulled sled signal output transistors but no problem there. Both of them in working order (hfe 165 and 153).
I still can't identify where the source of my problem lays. Could it be somewhere in sled drive circuitry? There is an IC with 4 op amps and one, strange to me, (switching?) IC.
Here is the video of sled coil signal:

Is the sled moving when it makes that signal? It should be!

 

[Ullar]

Is the sled moving when it makes that signal? It should be!

It looks like sled is pressed towards center of the disk.
When I move pick-up to the outermost position and start the player pick-up moves to the center and remains there.
Too much positive voltage?

 

[dr*audio]

It looks like sled is pressed towards center of the disk.
When I move pick-up to the outermost position and start the player pick-up moves to the center and remains there.
Too much positive voltage?

When started, the pickup should move to the center then move back. The tracking servo signals look normal to me so I think the problem is in the sled servo.

 

[Ullar]

When started, the pickup should move to the center then move back. The tracking servo signals look normal to me so I think the problem is in the sled servo.

Thank you dr*audio. Very much appreciated.
Any suggestions about trouble shooting the sled servo circuitry?
Here is the schematics:

 

[dr*audio]

That schematic is so blurry it hurts my eyes to look at it. When you load the CD:
1. look at the emitter of Q161 with a scope on DC coupled. Make sure it goes positive and negative.
2. Look at IC103 pin 1. Same thing.

 

[Ullar]

That schematic is so blurry it hurts my eyes to look at it. When you load the CD:
1. look at the emitter of Q161 with a scope on DC coupled. Make sure it goes positive and negative.
2. Look at IC103 pin 1. Same thing.

Thanks again, dr*audio. Sorry for the quality of the schematic. I put the link for the original below. It's downloaded from hifiengine and the only scan I've been able to find.
Now to the matter at hand.
1. Signal at the emitter of Q161 looks more or less symmetrical to 0V. Yes, it goes positive and negative.
2. Pin1 of IC103 stays mostly few volts positive, changing quite wildly but falls below 0V about once every 10 seconds. So yes, it does go both negative and positive.
I took a close look on sled, and noticed that it actually nudges a little bit back and forth during TOC search.

SL-P1300 service manual

 

[dr*audio]

What are IC103 pins 8 and 14 doing?

 

[Ullar]

What are IC103 pins 8 and 14 doing?

IC103 pin 8 is 0.2 V rising occasionally up to 0.4 V for about half of second.
IC103 pin 14 is centered at 0 V, 0.04 to 0.1 Vpp.
Does that make sense?

 

[McPint]

Hello,
can anyone shed some light on what's wrong with my Sony CDP-990?
When I insert a CD nothing happens. I disassembled the CD and noticed that the pickup won't move. I can move it spinning the gears manually.
I tested the sled motor by removing all the gears and applying 1V. It started spinning but when the gears are in and the tray is closed, it won't do anything at all.
Voltage on the motor is always at 0.15V.
The IN (home?) switch seems fine, I tested the continuity on the main board and it worked as expected.
What else could I check?
Any help is appreciated.

 

[Ullar]

Hello,
can anyone shed some light on what's wrong with my Sony CDP-990?
When I insert a CD nothing happens. I disassembled the CD and noticed that the pickup won't move. I can move it spinning the gears manually.
I tested the sled motor by removing all the gears and applying 1V. It started spinning but when the gears are in and the tray is closed, it won't do anything at all.
Voltage on the motor is always at 0.15V.
The IN (home?) switch seems fine, I tested the continuity on the main board and it worked as expected.
What else could I check?
Any help is appreciated.

Hi,
Nice piece of equipment you have over there
Does the sled move if you first move it to the outer edge (rotating the gears) and then switch on the player?
If not, you may have a problem with sled drive circuitry. Could be some electrolytic capacitors gone bad.

 

[McPint]

Hi,
Nice piece of equipment you have over there
Does the sled move if you first move it to the outer edge (rotating the gears) and then switch on the player?
If not, you may have a problem with sled drive circuitry. Could be some electrolytic capacitors gone bad.

Thanks! I finally managed to reassemble my hifi system after relocating, the CD player is badly missed!
No, it won't move at all. Maybe I'm missing some switch other than the IN switch?
I'd expect the voltage on the motor to change even with bad capacitors, or am I wrong?