Yes, but then the optical output reduces and you get less reflected light from the disc surface (so lower RF level).
So, by your words I can deduce that it cannot be repaired, so I think the best option is to buy a cheap unit mounting CDM4/19
It seems that way. You have fitted a different pickup earlier and proved it all works and adjusts OK. This pickup has excessive laser current and you have low RF output. The output also falls after 10 seconds or so from cold.
It all points to either a failed laser diode or possibly a pickup that has sustained mechanical damage (internal alignment of the optics) and you are artificially turning the current up to a very high value to compensate but then after a few seconds the chip gets so hot the light emission falls away.
Either way it not really fixable by normal means.
It all points to either a failed laser diode or possibly a pickup that has sustained mechanical damage (internal alignment of the optics) and you are artificially turning the current up to a very high value to compensate but then after a few seconds the chip gets so hot the light emission falls away.
Either way it not really fixable by normal means.
Hi guys! I'm working again with this cd player.
Bought a cheap unit (AK601) and used it's CDM4/19. Only needed to change the connector of the cd motor.
Adjusted to 50mv (Laser) with no problems. The laser pot is almost at maximum, but reached 50mv so I'm happy.
I also measured the laser current by measuring the voltage across R3522 (18ohm) reading 1,013V
So... 1,013 / 18 = 0,056V -> 56mV
I think it's perfect.
The only trouble here is the Focus. Since I have not a philips test CD, I have chosen 4 of my best pressings in my collection. Tried one by one and writing down the results.
I've realized that first tracks of every CD give different results than last tracks. For example, Track 1 reads between 380 and 390mV but Track 11 oscillates between 120mV and 240mV. This phenomenon happened also with the original CDM. And happens with other cd players I have, so I think that it's an inherent issue on CD's.
Here you have the results with this 4 CD:
CD1: First tracks 390mV, Last tracks between 120mV and 240mV. -> Bad mV reading (low) only with last tracks.
CD2: First tracks 420mV, Last tracks between 360mV and 380mV. -> Perfect mV reading.
CD3: First tracks 405mV, Last tracks between 380mV and 385mV. -> Perfect rmV eading.
CD4: First tracks 320mV, Last tracks between 300mV and 310mV. -> Bad mV reading (low) in all CD.
What I did is to put back CD4 and adjusted to reach 360mV (+40mV) on first tracks, so the table now looks like that:
CD1: First tracks 430mV, Last tracks between 160mV and 280mV. -> Again bad mV reading (low) only with last tracks, BUT playing well.
CD2: First tracks 460mV, Last tracks between 400mV and 420mV. -> Perfect mV reading.
CD3: First tracks 405mV, Last tracks between 380mV and 425mV. -> Perfect mV reading.
CD4: First tracks 360mV, Last tracks between 340mV and 350mV. -> Good mV reading in all CD.
With this values, I closed the unit assuming that it's well adjusted. Used it a few days playing perfect, until today. I was playing this (CD2) and first tracks started to jump. Opened the player again and measured Laser, reading 47mV so that's perfect. Measured Focus, reading between 110 and 240mV!!!!!! (a difference of 130mV) and obviously a very low level in both cases. Checked the CD and it's flat, shiny... it looks like a new CD.
So what I did is to adjust the pot to reach values near 360mV. Obviously the values in the previous table (the 4 CD's) have increased considerably, but still playing perfect.
Now (apparently) all CD's plays perfect, no jumps, no issues. Can I assume that it's well adjusted?
Or I can use a better method to adjust the focus?
Thanks!!
Bought a cheap unit (AK601) and used it's CDM4/19. Only needed to change the connector of the cd motor.
Adjusted to 50mv (Laser) with no problems. The laser pot is almost at maximum, but reached 50mv so I'm happy.
I also measured the laser current by measuring the voltage across R3522 (18ohm) reading 1,013V
So... 1,013 / 18 = 0,056V -> 56mV
I think it's perfect.
The only trouble here is the Focus. Since I have not a philips test CD, I have chosen 4 of my best pressings in my collection. Tried one by one and writing down the results.
I've realized that first tracks of every CD give different results than last tracks. For example, Track 1 reads between 380 and 390mV but Track 11 oscillates between 120mV and 240mV. This phenomenon happened also with the original CDM. And happens with other cd players I have, so I think that it's an inherent issue on CD's.
Here you have the results with this 4 CD:
CD1: First tracks 390mV, Last tracks between 120mV and 240mV. -> Bad mV reading (low) only with last tracks.
CD2: First tracks 420mV, Last tracks between 360mV and 380mV. -> Perfect mV reading.
CD3: First tracks 405mV, Last tracks between 380mV and 385mV. -> Perfect rmV eading.
CD4: First tracks 320mV, Last tracks between 300mV and 310mV. -> Bad mV reading (low) in all CD.
What I did is to put back CD4 and adjusted to reach 360mV (+40mV) on first tracks, so the table now looks like that:
CD1: First tracks 430mV, Last tracks between 160mV and 280mV. -> Again bad mV reading (low) only with last tracks, BUT playing well.
CD2: First tracks 460mV, Last tracks between 400mV and 420mV. -> Perfect mV reading.
CD3: First tracks 405mV, Last tracks between 380mV and 425mV. -> Perfect mV reading.
CD4: First tracks 360mV, Last tracks between 340mV and 350mV. -> Good mV reading in all CD.
With this values, I closed the unit assuming that it's well adjusted. Used it a few days playing perfect, until today. I was playing this (CD2) and first tracks started to jump. Opened the player again and measured Laser, reading 47mV so that's perfect. Measured Focus, reading between 110 and 240mV!!!!!! (a difference of 130mV) and obviously a very low level in both cases. Checked the CD and it's flat, shiny... it looks like a new CD.
So what I did is to adjust the pot to reach values near 360mV. Obviously the values in the previous table (the 4 CD's) have increased considerably, but still playing perfect.
Now (apparently) all CD's plays perfect, no jumps, no issues. Can I assume that it's well adjusted?
Or I can use a better method to adjust the focus?
Thanks!!
The voltage across the resistor R3501 relates only to reflected light from the disc.
The focus voltage will vary disc to disc and is the voltage needed to position the lens in the vertical axis to achieve correct focus. There will be differences between discs and as the disc plays from inner to outer areas.
The quality and amplitude of the RF is what matters.
The focus voltage will vary disc to disc and is the voltage needed to position the lens in the vertical axis to achieve correct focus. There will be differences between discs and as the disc plays from inner to outer areas.
The quality and amplitude of the RF is what matters.
Yes I know 😉 that's why I measured also the current across the laser diode, reading 56mA
Having 50mV (R3501) and 56mA I can assume that laser pot is well adjusted.
Ok so next time I'll pay attention to the RF signal to adjust the focus. Thanks!!
Current is always flowing through something, voltage is measured across something 🙂
56ma current flow sounds spot on for a typical laser diode.
Checked RF signal across RF output and ground (same chip gnd leg) and obtained a much clearer signal than older posts:
Still low level but a beautiful wave.
Oscilloscope is set to 500mv/div (I think)
With “new” lens and well adjusted current and focus, still having a low? signal.
Maybe its a oscilloscope failure or maybe its my fault cuz I have not idea how to use it properly.
Here’s a full image of the oscilloscope panel:
Probe is well calibrated and set to X1. If I change it to x10 then the signal goes very very low (obvious).
Player is working perfect.
90% of my cd collection shows good Focus values (between 360 and 460mV)
The other 10% shows “high” values between 600 or +700 mV
Is this bad??
At this moment Im hearing a cd reading 590mV and sound is amazing.
Still low level but a beautiful wave.
Oscilloscope is set to 500mv/div (I think)
With “new” lens and well adjusted current and focus, still having a low? signal.
Maybe its a oscilloscope failure or maybe its my fault cuz I have not idea how to use it properly.
Here’s a full image of the oscilloscope panel:
Probe is well calibrated and set to X1. If I change it to x10 then the signal goes very very low (obvious).
Player is working perfect.
90% of my cd collection shows good Focus values (between 360 and 460mV)
The other 10% shows “high” values between 600 or +700 mV
Is this bad??
At this moment Im hearing a cd reading 590mV and sound is amazing.
Attachments
Last edited:
Also, the signal looks clearer (more defined) live than in the photos.
In last post I said it's a low level signal because the service manual says 2,5V
I don't know if that means that RF signal has to be 2,5V peak to peak.
I'm reading aprox 1,3V peak to peak and I think it's ok for most players.
In last post I said it's a low level signal because the service manual says 2,5V
I don't know if that means that RF signal has to be 2,5V peak to peak.
I'm reading aprox 1,3V peak to peak and I think it's ok for most players.
The calibrate trimmer in the probe only has effect in the x10 position and the amplitude goes low because you have to set the scope from 0.5v/div to 50mv/div to account for that. You then mentally make the leap to multiply all results by 10 as you use the probe.
Check the probe in the x10 position using the Cal output on the scope. I see it says 500mv on the output and that should be very accurate. With the probe in x10 you should see a perfect squarewave of 500mv peak to peak (so one square of deflection when set at 50mv/div). If the waveform is not perfectly square then adjust the trimmer in the probe.
Depends where you are measuring. Refer back to post #4 Pin #26 (HF in) would be around 1.2 volts peak to peak which is around what you are showing.
Well calibrated using x10.
Measured using x10 and still reading 1,3V peak to peak (pin 3).
If I measure Pin 26 (hf input) it shows nothing and player makes a sound like (TAK TAK) and stops playing.
What you are looking here is Pin 3, using x10 and scope set to 20mV scale.
Measured using x10 and still reading 1,3V peak to peak (pin 3).
If I measure Pin 26 (hf input) it shows nothing and player makes a sound like (TAK TAK) and stops playing.
What you are looking here is Pin 3, using x10 and scope set to 20mV scale.
I would have expected pin 3 to be 2.5v according to the circuit details.
I'm just having a rethink... I would really need one in front of me... but looking closer I think I'm wrong in what I said earlier. The HF in is going to be the input to an inverting amp stage and so that explains why you see no signal.
The 2.5 volts isn't the amplitude of the RF, it the mean DC level. So your measured 1.3 volts peak to peak sounds about right and is the typical value seen across many makes and models.
Sorry about that, my error there.
I'm just having a rethink... I would really need one in front of me... but looking closer I think I'm wrong in what I said earlier. The HF in is going to be the input to an inverting amp stage and so that explains why you see no signal.
The 2.5 volts isn't the amplitude of the RF, it the mean DC level. So your measured 1.3 volts peak to peak sounds about right and is the typical value seen across many makes and models.
Sorry about that, my error there.
Dont worry if you were wrong. Im just learning and you are helping me a lot. Im very thankful.
I was looking to older threads on which you posted years ago and you said that 1,3 V is ok for most players so I was thinking that you were wrong about the 2,5V 😅😅😂😂
Anyway, now the RF signal looks beautiful. Well…….. beautiful considering that the oscilloscope is too (too) old.
I noticed that different cd’s shows different RF signals. Some cds shows very clear signals, and other cd’s (just a few in my collection) shows a very blurry signal.
Do you remember a post where I said that the player was well adjusted, but hearing a specific cd it started to jump?? This cd is the only that shows a very blurry signal.
And also is the only CD that reads a very low level of focus. When other cd’s are adjusted around 400mv, I play back this specific cd and reads 70 or 100 mV in the inner part, and around 200 in outer parts. What I did is to increase the focus pot to read around 300mv (average) and the other cd’s obviously increased level to values around 500 or 600 in a few cases.
I did this to ensure this cd to play well, but I dont know if that’s a bad adjustment.
I was looking to older threads on which you posted years ago and you said that 1,3 V is ok for most players so I was thinking that you were wrong about the 2,5V 😅😅😂😂
Anyway, now the RF signal looks beautiful. Well…….. beautiful considering that the oscilloscope is too (too) old.
I noticed that different cd’s shows different RF signals. Some cds shows very clear signals, and other cd’s (just a few in my collection) shows a very blurry signal.
Do you remember a post where I said that the player was well adjusted, but hearing a specific cd it started to jump?? This cd is the only that shows a very blurry signal.
And also is the only CD that reads a very low level of focus. When other cd’s are adjusted around 400mv, I play back this specific cd and reads 70 or 100 mV in the inner part, and around 200 in outer parts. What I did is to increase the focus pot to read around 300mv (average) and the other cd’s obviously increased level to values around 500 or 600 in a few cases.
I did this to ensure this cd to play well, but I dont know if that’s a bad adjustment.
RF amplitude is determined by pit shape and quality, same for blurry eye patterns. Reflection quality also matters (translucent CDs don't reflect all the signal back).
Philips specified Philips test CD #5 for that very reason. Other manufacturers specify various CDs as they have a known amplitude and pit shape (quality). If you run through your music CDs, you will find a wide variation. Some will be warped, eccentric or translucent as well. Pinholes and scratches are local, variable defects as well.
Philips specified Philips test CD #5 for that very reason. Other manufacturers specify various CDs as they have a known amplitude and pit shape (quality). If you run through your music CDs, you will find a wide variation. Some will be warped, eccentric or translucent as well. Pinholes and scratches are local, variable defects as well.
Thanks for tour post anatech
Yes, by trying different cds I noticed exactly what you said.
If I test 10 of my cd’s results are very different.
The problem now is that I dont know what method I have to follow to adjust the focus.
The laser current is ok because all my cds shows values between 47mV and 50mV. I know that this measurement is only the light reflected on the cd… but 47 to 50 means that the laser is working well. And also the current through the diode (56mA)
Focus is the final stage.
As I dont have a philips test cd, I need a method to do it. Thats why I thought about trying 10 cds and adjust the pot to reach 400mv (average). But this is impossible because 2 of my cds reads very low values when pot is adjusted to 400mv with other cds.
This 2 cds are classical music (Archive) from the 80’s.
I tried other Archive cds from the same year (and obviously same pressing plant) and readed normal values (near 400mv). I dont understand why cds that look exactly the same (year, pressing plant…) shows very different results.
Yes, by trying different cds I noticed exactly what you said.
If I test 10 of my cd’s results are very different.
The problem now is that I dont know what method I have to follow to adjust the focus.
The laser current is ok because all my cds shows values between 47mV and 50mV. I know that this measurement is only the light reflected on the cd… but 47 to 50 means that the laser is working well. And also the current through the diode (56mA)
Focus is the final stage.
As I dont have a philips test cd, I need a method to do it. Thats why I thought about trying 10 cds and adjust the pot to reach 400mv (average). But this is impossible because 2 of my cds reads very low values when pot is adjusted to 400mv with other cds.
This 2 cds are classical music (Archive) from the 80’s.
I tried other Archive cds from the same year (and obviously same pressing plant) and readed normal values (near 400mv). I dont understand why cds that look exactly the same (year, pressing plant…) shows very different results.
Some old CD's (and I've seen this on Deutsche Gramophon in particular) can suffer from 'disc rot'. If you hold the disc up to a bright light you can see the mottled appearance if you look through the disc at the light. The silver layer also can look discoloured.
If the RF level is way down on some discs then it really sounds like a disc problem and there is nothing you can do about that I'm afraid.
If the RF level is way down on some discs then it really sounds like a disc problem and there is nothing you can do about that I'm afraid.
Find the CDs that measure very high, and very low. Put them aside. Then find some average and go with that. I was forced to buy all these test CDs at the time, $450 for the two Philips CDs and I got a break.
In real life your CD player will encounter all these. The manufacturer is attempting to set a "specified level" so it plays most CDs. You will always have CDs that fall way out of spec and play on some machines and not others. Single beam players deal with some defects better, and some three beam systems deal with others better. So don't sweat it too much.
In real life your CD player will encounter all these. The manufacturer is attempting to set a "specified level" so it plays most CDs. You will always have CDs that fall way out of spec and play on some machines and not others. Single beam players deal with some defects better, and some three beam systems deal with others better. So don't sweat it too much.