Hi all,
I recently got a NAD 510 in excellent optical condition for free, so I would like to get it to work again.
The problem is, the CD won't spin and all you get is a "No Disc" on the LCD.
The laser itself is at least not dead, you can see it go on and the lens tries to find focus as soon as a CD is being inserted.
I get output from the photo diodes, which are also present also after the preamplifier (TDA1302), so I assume this one is ok.
As the following servo processor has current inputs, this is hard to measure, but when lifting the output pins of the preamp, you get a signal following the movements of the lens.
But some reason, the motor is not being started, so either there is no focus found by the servo processor (TDA1301) or a focus ok command being sent to the decoder (SAA7345) is ignored. So the servo processor (TDA1301) turns off the laser after a few seconds.
The spindle motor is ok, there is definitely no motor control output from the decoder.
Does anyone have experience with this type of Philips chipset? The ICs can still be found on ebay, but I have no idea where to start. And there is no way for me to find out what exactly is going on on the communication lines between the chips and the µP. I only have an analog scope.
So there are mainly 4 scenarios:
1. the laser is merely too weak. But at least focus should be found as I get an output from any of the diodes?
2. The servo processor is defective in a way that it can not detect any reflection.
3. The decoder is defective and ignores the command.
4. Something is wrong with the communication bus. This would possibly imply a defective µP, and there is no point in trying to find one.
I found a few threads here, they all remained unsolved...
Maybe someone has a service manual? All informations I have come from the datasheets of the ICs, I do not have schematics.
Also, if someone has more experience than me in servicing CD Players, I would be thankful for any idea or advice.
Thanks,
Georg
I recently got a NAD 510 in excellent optical condition for free, so I would like to get it to work again.
The problem is, the CD won't spin and all you get is a "No Disc" on the LCD.
The laser itself is at least not dead, you can see it go on and the lens tries to find focus as soon as a CD is being inserted.
I get output from the photo diodes, which are also present also after the preamplifier (TDA1302), so I assume this one is ok.
As the following servo processor has current inputs, this is hard to measure, but when lifting the output pins of the preamp, you get a signal following the movements of the lens.
But some reason, the motor is not being started, so either there is no focus found by the servo processor (TDA1301) or a focus ok command being sent to the decoder (SAA7345) is ignored. So the servo processor (TDA1301) turns off the laser after a few seconds.
The spindle motor is ok, there is definitely no motor control output from the decoder.
Does anyone have experience with this type of Philips chipset? The ICs can still be found on ebay, but I have no idea where to start. And there is no way for me to find out what exactly is going on on the communication lines between the chips and the µP. I only have an analog scope.
So there are mainly 4 scenarios:
1. the laser is merely too weak. But at least focus should be found as I get an output from any of the diodes?
2. The servo processor is defective in a way that it can not detect any reflection.
3. The decoder is defective and ignores the command.
4. Something is wrong with the communication bus. This would possibly imply a defective µP, and there is no point in trying to find one.
I found a few threads here, they all remained unsolved...
Maybe someone has a service manual? All informations I have come from the datasheets of the ICs, I do not have schematics.
Also, if someone has more experience than me in servicing CD Players, I would be thankful for any idea or advice.
Thanks,
Georg
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Anything chip set related would be way down the list I suspect. First suspects would be either the pickup or something disc motor related. As you say, it wont spin unless focus is found but its worth checking the motor drive amp isn't being activated and the motor isn't spinning.
95% of faults like this are usually something simple... so don't go looking to hard at this stage. Check the supplies of course, that's always one of the first steps.
95% of faults like this are usually something simple... so don't go looking to hard at this stage. Check the supplies of course, that's always one of the first steps.
Thanks Mooly,
well, testing the supply rails is the first thing I do in such cases. They look fine with no ripple or similar. As far as I see (without a manual), they also arrive on all relevant pins on the ICs. I had tested the spindle and sledge motors too.
I also had a look at the spindle motor drive outputs on the decoder IC, they are of differential type and obviously remain unactivated. There is an amplifier afterwards (like a dual power opamp), which just does what it is supposed to do - nothing.
But as outputs supposedly are PW modulated (determined by a command on the system bus - so no chance to check this), I also might have made a measurement mistake. I will check this tomorrow and have a closer look at the integrators and power stages afterwards.
I could get a new laser of course, but there are quite a few threads to be found from people who had changed the laser to no avail, so I am sceptical.
The thing is, I don't know if the stopped motor is the cause or a symptom.
If anything would point to maybe the servo IC, which should send the Focus OK to the decoder by the control bus, I would get one and change it. They are still avaliable on ebay.
Georg
well, testing the supply rails is the first thing I do in such cases. They look fine with no ripple or similar. As far as I see (without a manual), they also arrive on all relevant pins on the ICs. I had tested the spindle and sledge motors too.
I also had a look at the spindle motor drive outputs on the decoder IC, they are of differential type and obviously remain unactivated. There is an amplifier afterwards (like a dual power opamp), which just does what it is supposed to do - nothing.
But as outputs supposedly are PW modulated (determined by a command on the system bus - so no chance to check this), I also might have made a measurement mistake. I will check this tomorrow and have a closer look at the integrators and power stages afterwards.
I could get a new laser of course, but there are quite a few threads to be found from people who had changed the laser to no avail, so I am sceptical.
The thing is, I don't know if the stopped motor is the cause or a symptom.
If anything would point to maybe the servo IC, which should send the Focus OK to the decoder by the control bus, I would get one and change it. They are still avaliable on ebay.
Georg
I think the photodiodes will give an output no matter what shines on them, even if its visible light. In other words you will see something happen.
If the motor drive amp isn't being told to run then you have to assume the motor itself is probably OK. If its a little DC motor then a quick check with a battery can be done. It should fly on 1.5 volts and a 9 volt battery can be used to quickly clean the commutator. Connect both ways around with the motor disconnected from the PCB.
Never say never for a chip fault but unless it is a known issue then I wouldn't automatically suspect it but I suppose that if you can turn up a lot of cases where replacing the pickup hasn't been a fix then it makes you wonder.
If the motor drive amp isn't being told to run then you have to assume the motor itself is probably OK. If its a little DC motor then a quick check with a battery can be done. It should fly on 1.5 volts and a 9 volt battery can be used to quickly clean the commutator. Connect both ways around with the motor disconnected from the PCB.
Never say never for a chip fault but unless it is a known issue then I wouldn't automatically suspect it but I suppose that if you can turn up a lot of cases where replacing the pickup hasn't been a fix then it makes you wonder.
Yes, you are probably right.
Thanks for making me think it over again.
I think it is clear that simply no reflection is being detected.
So I just cranked up laser power and initial reading occured. Seems that in fact the laser is dying. I will put the player aside for the moment and get a new laser.
Fiddling with the current trimmer was in fact about the last thing I wanted to try. If I had done this to a good laser I might have damaged it.
btw, the readings I got from the photo diodes did come from the laser, as it clearly made a difference when a CD was present and I could tell the exact moment when the laser was being switched off by the servo controller. Also the reading were related to the movement of the focus drive. The trouble is, you just see that something is happening but you do not know whether the values are ok or not.
Let's see if it works fine after laser replacement. If performance is promising I maybe will try some more things with the player (hopefully to make it better)
Cheers
Georg
Thanks for making me think it over again.
I think it is clear that simply no reflection is being detected.
So I just cranked up laser power and initial reading occured. Seems that in fact the laser is dying. I will put the player aside for the moment and get a new laser.
Fiddling with the current trimmer was in fact about the last thing I wanted to try. If I had done this to a good laser I might have damaged it.
btw, the readings I got from the photo diodes did come from the laser, as it clearly made a difference when a CD was present and I could tell the exact moment when the laser was being switched off by the servo controller. Also the reading were related to the movement of the focus drive. The trouble is, you just see that something is happening but you do not know whether the values are ok or not.
Let's see if it works fine after laser replacement. If performance is promising I maybe will try some more things with the player (hopefully to make it better)
Cheers
Georg
Yes, it seems that the laser power has degraded significantly.
You got to hand it to NAD, they also care about older products.
A few days after I sent them a request they mailed me a service manual.
While I am waiting for the new laser optics to arrive, I have taken some time to listen to the player. After several tries it manages to read 50-60 percent of my CDs. Its performance is decent, albeit not stellar. My old Arcam is a far more involving device.
I am interested to see if this can be improved a bit, so have already taken out the parallel 100nF ceramics at the outputs (does anybody know what these are supposed to be good for?) and bypassed the output decoupling caps. No need for them in my setup.
As soon as the player is working properly again, I am also planning to replace all electrolytics on the DA Board and try different opamps. Maybe later a separate regulator for the digital supply of the converter. And the mute transistors could be replaced by a relay.
Not sure yet if I will touch the topology of the filter section.
For some reason NAD had decided to use 2 active filtering stages after the differential amplifier (which is of course bandwith-limited, but even followed directly by a passive RC filter). So in fact 4 filtering stages. Maybe this contributes to a certain feeling of boredom in the player's performance.
It's all for the fun of it of course, the 510 was bottom of the line I think and actually a cheap player.
Cheers,
Georg
You got to hand it to NAD, they also care about older products.
A few days after I sent them a request they mailed me a service manual.
While I am waiting for the new laser optics to arrive, I have taken some time to listen to the player. After several tries it manages to read 50-60 percent of my CDs. Its performance is decent, albeit not stellar. My old Arcam is a far more involving device.
I am interested to see if this can be improved a bit, so have already taken out the parallel 100nF ceramics at the outputs (does anybody know what these are supposed to be good for?) and bypassed the output decoupling caps. No need for them in my setup.
As soon as the player is working properly again, I am also planning to replace all electrolytics on the DA Board and try different opamps. Maybe later a separate regulator for the digital supply of the converter. And the mute transistors could be replaced by a relay.
Not sure yet if I will touch the topology of the filter section.
For some reason NAD had decided to use 2 active filtering stages after the differential amplifier (which is of course bandwith-limited, but even followed directly by a passive RC filter). So in fact 4 filtering stages. Maybe this contributes to a certain feeling of boredom in the player's performance.
It's all for the fun of it of course, the 510 was bottom of the line I think and actually a cheap player.
Cheers,
Georg
I would have to see the circuit to hazard a guess what the ceramics might be for. Hopefully it doesn't use 4558 opamps though 
N channel JFET's might be a worthwhile option for the muting if the drive voltages are compatible. It would be a softer mute than bjt's but with care could be more than satisfactory.
N channel JFET's might be a worthwhile option for the muting if the drive voltages are compatible. It would be a softer mute than bjt's but with care could be more than satisfactory.
I would have to see the circuit to hazard a guess what the ceramics might be for. Hopefully it doesn't use 4558 opamps though
N channel JFET's might be a worthwhile option for the muting if the drive voltages are compatible. It would be a softer mute than bjt's but with care could be more than satisfactory.
Here is the output section. No 4558s
NAD uses a lot of film caps and the 200p in the last filter are even stryoflex.
The ceramics may be for stability reasons. Doubt they are really necessary. You see that NAD put quite an effort in the filter section. They certainly had a reason for that, but I do not know if this was the best idea.
For JFETs I think I would have to modify the control section, it is not capable of providing negative voltage.
edit: Really should take more time... the ceramics belong to the muting section, the output has mylar... Anyway, I think they can be omitted too, even it probably won't make a difference. Keep things simple ;-)
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The control voltage on the lower end of those 10k's would need to go to -5 volts to use FET's. Most bjt muting with NPN devices has the collector connected to ground and uses the very special 2SC2878 which has high gain even in a reverse polarity state.
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^ Link still works.
The NAD seems to use devices more suited to preamp use (so conventional high gain small signal devices). There might not be much you can do there.
The NE5532's. Great opamp when used for linear amplification but you might find a noticeable 'difference', 'improvement' in switching to something like FET input device for U11 and 12. There is a lot of low level high frequency hash kicking around the front of the filter and bjt opamps like the 5532 have been rumoured to get upset by this as the bjt front end partially tries to demodulate this hash causing non linearities.
Whether that mechanism is true or not, I have found the 5532 can be bettered by FET devices in that kind of location. If I said try a TL072 and trust your ears...…
(Or a GENUINE OPA2604
You might just like what you hear.)
HTTP 301 This page has been moved
^ Link still works.
The NAD seems to use devices more suited to preamp use (so conventional high gain small signal devices). There might not be much you can do there.
The NE5532's. Great opamp when used for linear amplification but you might find a noticeable 'difference', 'improvement' in switching to something like FET input device for U11 and 12. There is a lot of low level high frequency hash kicking around the front of the filter and bjt opamps like the 5532 have been rumoured to get upset by this as the bjt front end partially tries to demodulate this hash causing non linearities.
Whether that mechanism is true or not, I have found the 5532 can be bettered by FET devices in that kind of location. If I said try a TL072 and trust your ears...…
(Or a GENUINE OPA2604
You might just like what you hear.)
Thanks Mooly,
Interesting thing about the behavior of bjt Opamps, had not heard about that before.
I will use sockets anyway, so I can swap them.
Initially I was thinking of some newer device, like OPA2134 (also with FET input, btw), but I will give the 072 a try too. Anyway, my feeling is that a rather slow device like the TL072 may not be the best choice for filter applications.
Just had one more look at the muting circuit, it would at least take one additonal transistor and a few resistors to adapt it for the FETs. Don't think it's worth it. I will maybe go for the C2878 or do the relay solution. Just this also would need an additional transistor to invert the control signal, if done properly (muting on the normally closed contact).
I will do that later, given the caps and opamps bring satisfactory results. You cannot make a racing car out of a tractor.
Interesting thing about the behavior of bjt Opamps, had not heard about that before.
I will use sockets anyway, so I can swap them.
Initially I was thinking of some newer device, like OPA2134 (also with FET input, btw), but I will give the 072 a try too. Anyway, my feeling is that a rather slow device like the TL072 may not be the best choice for filter applications.
Just had one more look at the muting circuit, it would at least take one additonal transistor and a few resistors to adapt it for the FETs. Don't think it's worth it. I will maybe go for the C2878 or do the relay solution. Just this also would need an additional transistor to invert the control signal, if done properly (muting on the normally closed contact).
I will do that later, given the caps and opamps bring satisfactory results. You cannot make a racing car out of a tractor.
Erm.. Not forgetting that it's currently seriously wounded, as well.
Arcam isn't much of a milestone to measure against
......the 5532 can drive 600 ohm loads and is a low noise opamp..........
NE 5532 A(N,P)
Erm.. Not forgetting that it's currently seriously wounded, as well.
Arcam isn't much of a milestone to measure against
Well, the Arcam was one of the better "budget" players then. It is almost 30 years and still playing with lots of power. I like the kind of "excitement" in its music reproduction. But also has its drawbacks for sure.
I also thought that a 5532 would be a better choice, but I will give it try, just because I am curious. Sockets are already installed, but it will take a few days before I will be able to give it a serious listen.
In the meantime the CDM12 laser surgery has been finished successfully. Only the optical unit was exchanged. I almost messed it up when one of the small plastic parts that hold the sledge rod at its ends jumped from the tweezers and vanished for good. No use trying to fix this with elastic glue, the laser loses tracking at the end where the glue job is done. Seems that the small plastic lock provides just the right amount of clearance for the rod. I eventually ended up making a new one from a piece of a cable fastener.
The drive is reading in CDs fast now, just some CDRs may have a problem, although the TOC is being quickly recognized it won't play, with the CD spinning at full speed intil the player gives up with an error message. May be due to the Chinese aftermarket laser, I can live with this.
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CDR's on CDM12.1 and 12.4 pickups was always hit and miss. I found burning at the highest speeds (opposite of what you normally read) gave the best results. I verified this with an oscilloscope by looking the RF in playback. It will be PC and blank disc specific though.
Although the TL072 doesn't have the same outright drive ability as the 5532 you don't need that here. It will easily drive 600 ohm loads in this application (if you really want it to) because the signal levels are low. 2V RMS output (about the maximum from a CD player at 0db)into 600 ohm is only 3.3 milliamps RMS which is well within the TL072 capabilities.
Although the TL072 doesn't have the same outright drive ability as the 5532 you don't need that here. It will easily drive 600 ohm loads in this application (if you really want it to) because the signal levels are low. 2V RMS output (about the maximum from a CD player at 0db)into 600 ohm is only 3.3 milliamps RMS which is well within the TL072 capabilities.
Had a just little time yesterday to give it a short listen.
The TL072 do it ok, but not sure if better than the 5532s.
To no big surprise, the basic sound has not really changed, my feeling is that it lacks "definition". I will try to recap the DA board anyway, this will not cost a fortune.
At the moment, the old Arcam (which also got new electrolytics and opamps on the DA board recently) is definitely the better player.
The reason for fiddling with the NAD 510 was that I recently repaired a friend's NAD 514 and was surprised by its performance. Of course the interiors of the 514 are entirely different, it has a Sony drive and a Matsushita MASH converter. I was curious whether the (much cheaper) 510 would sound similar.
I will post the results when the caps are new.
The TL072 do it ok, but not sure if better than the 5532s.
To no big surprise, the basic sound has not really changed, my feeling is that it lacks "definition". I will try to recap the DA board anyway, this will not cost a fortune.
At the moment, the old Arcam (which also got new electrolytics and opamps on the DA board recently) is definitely the better player.
The reason for fiddling with the NAD 510 was that I recently repaired a friend's NAD 514 and was surprised by its performance. Of course the interiors of the 514 are entirely different, it has a Sony drive and a Matsushita MASH converter. I was curious whether the (much cheaper) 510 would sound similar.
I will post the results when the caps are new.
As with any modification you should give it time... sometimes expectations get in the way immediately following a component change.
Use it for a few days with different recorded material, and if you don't like or can't tell any difference with the TL072 after doing that then that's fine.
You may find after doing that and then reverting, that you then can tell the 5532 is better in this application, or maybe the 5532 suddenly doesn't sound quite like you thought.
So give it time over a few days. Live with it and see how it sounds day to day.
Use it for a few days with different recorded material, and if you don't like or can't tell any difference with the TL072 after doing that then that's fine.
You may find after doing that and then reverting, that you then can tell the 5532 is better in this application, or maybe the 5532 suddenly doesn't sound quite like you thought.
So give it time over a few days. Live with it and see how it sounds day to day.
Tried different things in the meantime.
The DA board got new electrolytics and a separate reg for the 7350's digital supply. The ceramics around the 7350s output stage were replaced by styroflex types. I also tried to take them out as sometimes is suggested, this did not work at all. The player sounded rather horrible afterwards. No big surprise actually, as they form an integrator within the 7350. I really wonder why this works out in some players.
The opamps are OPA2134s now. I found the TL072s sounded somewhat "thin", like lacking bass (which is probably not exactly the case, maybe this impression is due to some higher amount of distortion in th upper range, but I cannot prove it.) The good old 5532s on the other side sound rather boring. The 2134 seems to be a good compromise for the moment.
The probably baddest thing I did was a little bit of experimenting with the filter stages. As the IC are socketed now, it is easy to tap the output directly from the first filter stage which is has a multiple feedback topology, omitting the final LPF.
I may get considerably more sampling frequency trash at the outputs now, but to my ears it does not sound bad at all. With the final filter (which has its cutoff point at about 35kHz) mids appear rather undefined. Amazing given it's specs, maybe this is due to some phase behavior. No idea whether I will leave it this way. I also had thought of an LC filter like Marantz did, but I think this maybe won't be worth the effort.
Also the new electrolytics will take some time to break in, so let's see. I will stick to Mooly's suggestion and give it time.
The bigger problem is the drive, on several CDs it produces short dropouts on the outer tracks. Maybe the new laser just is not any better, or it had been damaged during shipment. So I thought I had nothing left to lose and turned up laser power by a tiny!! amount. Tracking on the outer tracks improved significantly, on the other hand, on some CDs that had been playing well before, the player had problems in finding the beginning of the first track then or even could not read the TOC. Very strange.
Put the trimpot about in the middle of the two settings and it seems I indeliberately found some compromise. Still not perfect on the outer tracks, but no problem with the beginnings so far.
Soundwise, the player starts to be fun to listen to, but still does not compare to my only slightly modified Arcam Alpha+.
If my less than competent modding of the humble NAD should eventually show some good results, I may try to get another Laser unit for it. But this may be a long way to go.
And the maybe I have the self-confidence to do some bigger modifications to my trusted Arcam.
The DA board got new electrolytics and a separate reg for the 7350's digital supply. The ceramics around the 7350s output stage were replaced by styroflex types. I also tried to take them out as sometimes is suggested, this did not work at all. The player sounded rather horrible afterwards. No big surprise actually, as they form an integrator within the 7350. I really wonder why this works out in some players.
The opamps are OPA2134s now. I found the TL072s sounded somewhat "thin", like lacking bass (which is probably not exactly the case, maybe this impression is due to some higher amount of distortion in th upper range, but I cannot prove it.) The good old 5532s on the other side sound rather boring. The 2134 seems to be a good compromise for the moment.
The probably baddest thing I did was a little bit of experimenting with the filter stages. As the IC are socketed now, it is easy to tap the output directly from the first filter stage which is has a multiple feedback topology, omitting the final LPF.
I may get considerably more sampling frequency trash at the outputs now, but to my ears it does not sound bad at all. With the final filter (which has its cutoff point at about 35kHz) mids appear rather undefined. Amazing given it's specs, maybe this is due to some phase behavior. No idea whether I will leave it this way. I also had thought of an LC filter like Marantz did, but I think this maybe won't be worth the effort.
Also the new electrolytics will take some time to break in, so let's see. I will stick to Mooly's suggestion and give it time.
The bigger problem is the drive, on several CDs it produces short dropouts on the outer tracks. Maybe the new laser just is not any better, or it had been damaged during shipment. So I thought I had nothing left to lose and turned up laser power by a tiny!! amount. Tracking on the outer tracks improved significantly, on the other hand, on some CDs that had been playing well before, the player had problems in finding the beginning of the first track then or even could not read the TOC. Very strange.
Put the trimpot about in the middle of the two settings and it seems I indeliberately found some compromise. Still not perfect on the outer tracks, but no problem with the beginnings so far.
Soundwise, the player starts to be fun to listen to, but still does not compare to my only slightly modified Arcam Alpha+.
If my less than competent modding of the humble NAD should eventually show some good results, I may try to get another Laser unit for it. But this may be a long way to go.
And the maybe I have the self-confidence to do some bigger modifications to my trusted Arcam.
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