The signal might not be present at the input pin of TDA8808T because:
1. Coupling caps (as you mentioned) could be faulty. Did you check the presence of the signal BEFORE the caps? If the signal is not there - the caps are probably ok.
2. Tracks could be open.
3. Faulty TDA8808T might be shorting these signals to ground. Cut the input pin and check again for signal presence.
4. There might be some sort of "reflectivity adjustment" (to accommodate CD-RW ROM reflectivity as well as standard CD ROM's reflectivity) done via transistors - usually darlingtons. They could be faulty (not likely but possible), or the control signal might be present at all times, or too high / low (more likely).
Maybe someone could help with a circuit diagram………
Good luck
Extreme_Boky
1. Coupling caps (as you mentioned) could be faulty. Did you check the presence of the signal BEFORE the caps? If the signal is not there - the caps are probably ok.
2. Tracks could be open.
3. Faulty TDA8808T might be shorting these signals to ground. Cut the input pin and check again for signal presence.
4. There might be some sort of "reflectivity adjustment" (to accommodate CD-RW ROM reflectivity as well as standard CD ROM's reflectivity) done via transistors - usually darlingtons. They could be faulty (not likely but possible), or the control signal might be present at all times, or too high / low (more likely).
Maybe someone could help with a circuit diagram………
Good luck
Extreme_Boky
Hi Boky,
Yes in my last post I mentioned that clean HF was present at the 100K pullup resistor, perhaps I wasn't clear enough, but the signal is present on one side of the cap (pullup resistor side) and not the other - the 8808T side of the cap. Unfortunately this does not necessarily mean that cap is bad, the 8808 input could be shorted internally. I did note that the supposed HF input impedance of the 8808T is extremely low, and not knowing the capacitance of that capacitor means I don't really know what to expect in terms of normal amplitudes at that point in the circuit.
All board traces are intact, and I have verified continuity everywhere on the board.
My first move will be to replace that capacitor, then if warranted I will replace the 8808 once the replacements arrive. Before replacing the chip though I will double check to make sure that the servo signals going to the 8808 are present.
Kevin
Yes in my last post I mentioned that clean HF was present at the 100K pullup resistor, perhaps I wasn't clear enough, but the signal is present on one side of the cap (pullup resistor side) and not the other - the 8808T side of the cap. Unfortunately this does not necessarily mean that cap is bad, the 8808 input could be shorted internally. I did note that the supposed HF input impedance of the 8808T is extremely low, and not knowing the capacitance of that capacitor means I don't really know what to expect in terms of normal amplitudes at that point in the circuit.
All board traces are intact, and I have verified continuity everywhere on the board.
My first move will be to replace that capacitor, then if warranted I will replace the 8808 once the replacements arrive. Before replacing the chip though I will double check to make sure that the servo signals going to the 8808 are present.
Kevin
Haven't had too much time to work on the lambda lately, but thought I would try replacing the coupling capacitor at the HF input of the TDA8808T which incidentally is a 470pF capacitor. This didn't fix the problem, I was somewhat hopefull that it was the reason why there was no signal at the input of the 8808T.
Perhaps the cap was good and I just didn't get a good contact on the chip side.
I modeled the diodes as a current source, used the same circuitry as used in the HF branch and determined that the high levels of HF I measured would not be there if the chip was good and was presenting the roughly 500 ohm - 1K input impedance to the diodes that is listed in the spec. The individual diode current is on the order of a few uA typically.
Based on what little I know it seems like the TDA8808T HF input might be bad. I am doubtful however, but the chip is easy to replace with the tools available at work, just waiting for that part..
Perhaps I am chasing a red herring, but without a real schematic and some minimal information as to waveforms and amplitudes this is discouraging.
I am certain I can fix it, but on the other hand shotgunning every related component is going to be expensive, and time intensive.
I am still awaiting the arrival of the TDA8808T's and TDA8809T's I ordered a couple of weeks ago from the UK.
Including these chips, the pickup and some smd parts for the loader board this unrequited repair attempt has so far cost me over $150.
I doubt this makes much economic sense, and talking to a couple of telecom experts here about the design of the Lambda makes it questionable as to whether it is really worth it.
There are blatant design errors I can see when looking at even the incomplete schematic, to wit:
* 74HC74 flip flop are used to reclock the spdif and aes/ebu outputs. The problem with this is the clock to data propagation uncertainty which is at least several ps, and the fact that they are being used differentially. (Most 74 series logic uses an inverter for generating Q_bar so there is a delay between Q and Q_bar)
* AES/EBU output impedance is not 110 ohms balanced.
* Unused opamps feature both inputs grounded, so depending on differential offset levels they may oscillate or just toggle occasionally.
* Power on reset circuit is inconsistent.
* TDA8808T and TDA8809T are on separate boards, and connections run over low quality ribbon cable and IDC connectors.
* VFD (no schematic) filaments operate even when display is shut off.
The biggest thing seems to be the almost total lack of documentation..
Kevin
Perhaps the cap was good and I just didn't get a good contact on the chip side.
I modeled the diodes as a current source, used the same circuitry as used in the HF branch and determined that the high levels of HF I measured would not be there if the chip was good and was presenting the roughly 500 ohm - 1K input impedance to the diodes that is listed in the spec. The individual diode current is on the order of a few uA typically.
Based on what little I know it seems like the TDA8808T HF input might be bad. I am doubtful however, but the chip is easy to replace with the tools available at work, just waiting for that part..
Perhaps I am chasing a red herring, but without a real schematic and some minimal information as to waveforms and amplitudes this is discouraging.
I am certain I can fix it, but on the other hand shotgunning every related component is going to be expensive, and time intensive.
I am still awaiting the arrival of the TDA8808T's and TDA8809T's I ordered a couple of weeks ago from the UK.
Including these chips, the pickup and some smd parts for the loader board this unrequited repair attempt has so far cost me over $150.
I doubt this makes much economic sense, and talking to a couple of telecom experts here about the design of the Lambda makes it questionable as to whether it is really worth it.
There are blatant design errors I can see when looking at even the incomplete schematic, to wit:
* 74HC74 flip flop are used to reclock the spdif and aes/ebu outputs. The problem with this is the clock to data propagation uncertainty which is at least several ps, and the fact that they are being used differentially. (Most 74 series logic uses an inverter for generating Q_bar so there is a delay between Q and Q_bar)
* AES/EBU output impedance is not 110 ohms balanced.
* Unused opamps feature both inputs grounded, so depending on differential offset levels they may oscillate or just toggle occasionally.
* Power on reset circuit is inconsistent.
* TDA8808T and TDA8809T are on separate boards, and connections run over low quality ribbon cable and IDC connectors.
* VFD (no schematic) filaments operate even when display is shut off.
The biggest thing seems to be the almost total lack of documentation..
Kevin
I communicated with Theta on the 75 ohm AES EBU. They said at the time of the design there was uncertainty of what "balanced digital" in consumer products should be. They opted for 75 ohm. The two resistors that set this impedance are easily replaced with 55 ohms to give the required 110.
The output really is SPDIF in balanced mode, not AES EBU...
The output really is SPDIF in balanced mode, not AES EBU...
Hi Tubenut,
Yes that's true, I plan to change those resistors to 55 ohms once (if ???) I get the drive running again.
There are a couple of differences between the "pro" and "consumer" versions of the AES/EBU interface, in the professional version the subcode usually contains ASCII strings for identification of source and destination, and in the consumer version (spdif/aes) the subcode would carry scms information if present. (I suspect that given the age of the spdif interface IC in the lambda the scms function might not be supported. In some newer applications scms subcode can prevent codecs from outputting anything other than the analog stream - take a look at the PCM2906 as an example.) Other differences are that the last four bits in true aes/ebu words are not audio, however in spdif/ consumer aes/ebu up to 24 bits of audio are directly supported.
For anyone interested there is more on spdif and aes/ebu at:
www.epanorama.net/documents/audio/spdif.html
Still waiting on that 8808T to show up to try the next step...
Kevin
Yes that's true, I plan to change those resistors to 55 ohms once (if ???) I get the drive running again.
There are a couple of differences between the "pro" and "consumer" versions of the AES/EBU interface, in the professional version the subcode usually contains ASCII strings for identification of source and destination, and in the consumer version (spdif/aes) the subcode would carry scms information if present. (I suspect that given the age of the spdif interface IC in the lambda the scms function might not be supported. In some newer applications scms subcode can prevent codecs from outputting anything other than the analog stream - take a look at the PCM2906 as an example.) Other differences are that the last four bits in true aes/ebu words are not audio, however in spdif/ consumer aes/ebu up to 24 bits of audio are directly supported.
For anyone interested there is more on spdif and aes/ebu at:
www.epanorama.net/documents/audio/spdif.html
Still waiting on that 8808T to show up to try the next step...
Kevin
Latest is parts are finally on their way from the UK after months of delay.. I have no idea whether I will ever be able to fix this machine.. I will replace the TDA8808 and see where that gets me. Haven't devoted much time or energy to it lately and I now consider the Lambda to be dispensable.
Well, if you have the signal present at the coupling capacitor input pin, the capacitor
is ok AND there is no signal at the output capacitor leg (pin), TDA input pin is probably shorting signal to ground. The slightest impedance changes here would affect the RF signal to the point where nothing will work.
Unsolder the TDA8808 input pin and check if signal re-appears at the output capacitor leg. If it does (and I bet it will!), replace the TDA chip.
The PCB track between output capacitor leg and TDA input pin could have cracked…
Good luck,
Extreme_Boky
Hi Boky,
Looked at all that months ago.. The input impedance of the TDA8808T is only about 1K according to the specs I was able to dig up. The diodes are essentially current sources and based on measurements and modeling I was able to do the voltages present at the input of the 8808 should be well within acceptable limits.
The chip itself might be bad, more likely it is a lousy implementation that was fine tuned to one run of the pickup assembly and does not work properly with any devices that slightly differ from the originals. After much study and reading up on good digital design practices I have concluded that the Lambda is not nearly as good as it's cracked up to be, it is probably the case that most other players I have encountered are just worse..
The parts in this thing are seriously obsolete and very difficult to get in this country in the limited quantities I need to repair it. The replacement parts I ordered months ago were just shipped last week from the UK and will probably take a while to get here. Philips recently removed all of the data sheets on the chip set used in this player from their semiconductor business's website..
I have got to decide how much more time and effort is warranted, not to mention money - given that I no longer have any need for it.
Obviously I am worried that I could get into an endless spiral of parts replacement without fixing the problem, so I have decided to work on it on a casual basis and not to spend any more money on it should the TDA8808/9 chips I purchased not resolve the problem.
I will probably end up putting it on eBay as a repair/parts unit should this last effort prove unsuccessful.
Kevin
Looked at all that months ago.. The input impedance of the TDA8808T is only about 1K according to the specs I was able to dig up. The diodes are essentially current sources and based on measurements and modeling I was able to do the voltages present at the input of the 8808 should be well within acceptable limits.
The chip itself might be bad, more likely it is a lousy implementation that was fine tuned to one run of the pickup assembly and does not work properly with any devices that slightly differ from the originals. After much study and reading up on good digital design practices I have concluded that the Lambda is not nearly as good as it's cracked up to be, it is probably the case that most other players I have encountered are just worse..
The parts in this thing are seriously obsolete and very difficult to get in this country in the limited quantities I need to repair it. The replacement parts I ordered months ago were just shipped last week from the UK and will probably take a while to get here. Philips recently removed all of the data sheets on the chip set used in this player from their semiconductor business's website..
I have got to decide how much more time and effort is warranted, not to mention money - given that I no longer have any need for it.
Obviously I am worried that I could get into an endless spiral of parts replacement without fixing the problem, so I have decided to work on it on a casual basis and not to spend any more money on it should the TDA8808/9 chips I purchased not resolve the problem.
I will probably end up putting it on eBay as a repair/parts unit should this last effort prove unsuccessful.
Kevin
It's been several months now since I ordered those chips, and 4 of them by royal airmail should not have cost more than a couple of quid for shipping.. Sooo I am assuming that they went by surface mail, probably by paddle steamer..
Anyway I have just about totally lost interest in fixing this thing. I am sure it can be repaired by the right person.
If anyone is interesting in acquiring it make a reasonable offer by pm.
direct<dot>heated<at>gmail.com
Anyway I have just about totally lost interest in fixing this thing. I am sure it can be repaired by the right person.
If anyone is interesting in acquiring it make a reasonable offer by pm.
direct<dot>heated<at>gmail.com
Hello!
Can anybody help me and tell what is the chips with "?" simbol on this picture?
https://www.dropbox.com/s/y557xd8ndxu41xq/IMG_6132.JPG
I have Service manual for this model, but there is no info.
I have marking erased in my device...
And can anybody measure sense voltage?
It is CN3 connector in supply board:
https://www.dropbox.com/s/yocvenl41wei4k5/supply board CN3 to control board PS Lambda I.JPG
I need voltage DGND-SENS.
Can anybody help me and tell what is the chips with "?" simbol on this picture?
https://www.dropbox.com/s/y557xd8ndxu41xq/IMG_6132.JPG
I have Service manual for this model, but there is no info.
I have marking erased in my device...
And can anybody measure sense voltage?
It is CN3 connector in supply board:
https://www.dropbox.com/s/yocvenl41wei4k5/supply board CN3 to control board PS Lambda I.JPG
I need voltage DGND-SENS.
Last edited:
Kevin, A few years down the road I write this. Like 10. My Lambda just developed a symptom today and I'm thinking that it is some sort of mechanical issue and not anything more complicated but then even mechanical would be complicated considering the status of parts availability. Everything is working fine but all of a sudden the drive mechanism.. or specifically the mechanism that is actually spinning has become noisy. I have not opened it up yet so suffice to say it just sounds like the whisk whisk of a platter spinning. Any notion of what this could be? Im surprised I didnt just open it up to at least look and run it with the top off but I guess I didnt want to believe it happened although in the back of my mind ,,, I half expected something due to the age of this Lambda. Its also the first version and exceptionally clean.
Lambda "rub"
took the cover off and ran it and spun it when off as well. A little light tweaking with fingers on the assembly.. and cleaned off the spindle(?) as appeared a bit dirty. Don't know if a dirty spindle would cause that,, maybe if the disc doesnt seat properly? At any rate, back to working fine. One particularly strange even is when I was powering off or on when I was working on it a horrendous electronic noise was generated.. It ceased though but cant imagine that such a noise would erupt and then be gone after cycling through power on/off. I had thought I didnt even touch anything --where did that come from. All ok for now..
took the cover off and ran it and spun it when off as well. A little light tweaking with fingers on the assembly.. and cleaned off the spindle(?) as appeared a bit dirty. Don't know if a dirty spindle would cause that,, maybe if the disc doesnt seat properly? At any rate, back to working fine. One particularly strange even is when I was powering off or on when I was working on it a horrendous electronic noise was generated.. It ceased though but cant imagine that such a noise would erupt and then be gone after cycling through power on/off. I had thought I didnt even touch anything --where did that come from. All ok for now..
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.