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Marantz CD-73: not recognizing disc, laser seems fine, voltages differ oddly from SM?
Marantz CD-73: not recognizing disc, laser seems fine, voltages differ oddly from SM?
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Old 14th December 2020, 05:52 PM   #21
N101N is offline N101N
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Join Date: May 2018
joydivision,
would it be appalling to suggest a nonoversampling 44/16 DAC without reclock and a grounded base discrete analog amplifier?
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Old 23rd December 2020, 07:34 PM   #22
joydivision is offline joydivision  Portugal
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Join Date: Feb 2007
Location: Algarve
So, unfortunately this had another turn-around and so I'm asking for some opinions. The player is still not ready to go back to its owner (luckily the problem has occured here, not already at owner's), as it still has one intermittent and odd problem:

sometimes (I'd even say, RARELY), instead of the beautiful sound, it outputs harsh digital noise (still some music recognizable very low), mostly on one of the channels, sometimes on both, sometimes one (once even happened with both!) channel simply outputs silence, no noise but no music either. What has also happened is that while it is playing well, suddenly some of the noise starts randomly on one of the channels, getting worse, or eventually getting a little better again, one time it even disappeared again, being back to normal!

As this could be a bad connection, I've tried everything "obvious", like knocking around the decoder PCB with a plastic tool while listening to playback so to try and discover bad solder joints, I've moved every cable trying to find bad connections, I've knocked around and shaken the player, and connections while playing, nothing, except for the poking on the PCB, which was slightly changing the character of the sound on one place (making me suspect of bad solder joints, so I resoldered almost whole decoder PCB), that issue was then eliminated, but unfortunatley, the noise issue wasn't gone, after some hours playing it has happened again.

As it happens so rarely, it's really frustrating to hunt down, I've had the player open and scope ready, and was lucky enough to "catch" the signal for some minutes, it looks a little similar to RF (eye pattern) signal, but in a totally different frequency domain (audio frequencies). Does this mean that somehow the RF signal is modulating the audio signal due to some intermittent "short" or something? Or that decoding stages fail? Then the fault was gone and I couldn't do any more measurements...

It's really time consuming and at this time I can't continue this (our second child is going to be born soon in January, so this will rest for some weeks), but I'd really like to hear some opinions on what this could be. I did a lot of research (on here and other places) for similar noise problems and their causes. Here's a resume of the player's condition and then I'll follow with a list of possible causes on which I'd like to hear opinions. As said, no hurry, lots of time to think and research and plan, so that when I can finally continue working on this, I'll know how to tackle this.

Just a quick reminder and remark that this problem is there SINCE the start, wasn't caused by me changing capacitors (remember me writing somewhere in the beginning of this thread, when I had the player back to reading discs, that one channel was dead? Then later, without me doing anything, that problem had magically gone away? Well it hadn't, actually...

Present condition:

- Laser is fine

- Pressed discs are read very well, no intermittent problems, only some CD-R not so good (skips on some tracks), but other CD-Rs fine, due to age and mech used (CDM-0) this seems normal (have researched this)

- Power supply is fine, although I haven't measured voltages DURING the fault occurring

- I replaced all relevant electrolytic caps

- When fault not occurring, sound is absolutely fine

- Player doesn't show any trouble reading disc even while the problem occurs, so I'm pretty sure it has nothing to do with the mech and subsequent circuitry. But it could be caused in later digital stages (decoder).

- On some rare occasions, the orange and green LEDs for track display may flicker a bit, but I've read they can develop bad solder joints/connections in display panel, in the present player it's not serious (very rare and never stops displaying) and dismantling panel is quite difficult, also this happens on occasions when sound is absolutely fine, so I'm pretty sure it's unrelated and haven't bothered yet with solving this

- When I switch player on or off, it makes noticeable "pop" in audio output for 1/2 second, but it's kind of harsh, sharp, reminds a tiny little bit the noise that is heard while fault is occurring. As I've never had this model of player in my hands, I can't be sure this is normal or not... This has also been without change since I received the player, so not caused by me. Anyone knows? I've seen some other cd players do this, so it could be normal, but usually it's more like a "pop" or "thump", not so harsh/sharp/high frequency loaded...


What I researched:

- digital noise (with some audio present) can be caused by bad RAM chip for error correction. But normally, this kind of fault is permanent and appears in both channels. Does anyone know if this can also appear "randomly" like here and affect only one channel? Remember this player has dual TDA1540.

- digital noise can be caused when TDA1540 doesn't receive -18V supply or if that voltage goes bad randomly (or rises, for example). I wasn't able to measure that voltage while the fault occurs, yet. When fault is not present, -18V supply (as all others, I even scoped them) is fine.

- Any possibility of being the reed (KILL/muting) relays in audio out? I hadn't the chance to follow the audio signal while fault occurring, yet. But I don't think a failing reed relay would cause this kind of noise, right? It would only interrupt the sound, right? This player has no muting transistors, only reed relays.

- could a defect in audio opamps cause this? Not possible, right? I wasn't able, as already said, to follow audio signal while fault occurs, yet.

- this kind of noise can be caused by defective TDA1540, this could explain why mostly in one channel (one of them would be in a worse shape than the other), but it doesn't make much sense, as for what I read, this normally means that the fault happens consistently when player gets warm (chip gets hot). I've used the player extensively, sometimes for a couple of hours continously without problem occurring, and it has occurred sometimes when I switch the player on after one day without use, so while cold, but it also has appeared suddenly while playing, being warm...
I know that this can be narrowed down by applying freeze spray topically to TDA1540.

- This player has that "odd" Sony decoder piggy board. This has one of the the (in)famous griplets, actually the only one of the whole player. Could this cause anything like noise?

Thanks in advance!
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Old 23rd December 2020, 09:05 PM   #23
Markw4 is offline Markw4  United States
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Join Date: Jul 2016
Location: California
Only thing that comes to mind at the moment is that you have two channels. You might be able to swap some components or circuit functions from one channel to the other and see if the problem moves with it.
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Old 25th December 2020, 07:00 PM   #24
joydivision is offline joydivision  Portugal
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Join Date: Feb 2007
Location: Algarve
Yes, that's a good suggestion especially for checking if the fault lies in the tda1540, as they are in sockets, it's easy to swap them. I'll definitely try that when I got the player open on bench for testing, if the fault occurs being present only in one channel.

Merry Christmas :-)
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Old 31st December 2020, 03:29 PM   #25
joydivision is offline joydivision  Portugal
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Join Date: Feb 2007
Location: Algarve
So, I managed to find a couple of hours to dismantle it again, install it on the bench in a way it could play while doing some further tests. Now, for at least three weeks I won't be able to do anything else, but at least it's sitting there ready for more testing and I already did some of them (and might even have eliminated the problem, but it needs testing). This is what I did (and found):

- both TDA1540 run cold, so I can't imagine that they would be dying (while I was testing, the noise only appeared ONCE, right at the start, when player was cold, then disappeared before I could do much measurements...). Haven't swapped them, as I couldn't notice that noise problem would affect only one channel (when it briefly appeared, seemed to affect BOTH channels, but then I was using headphones, so I might have heard wrong, it stayed only for a few seconds).

- SAA7030 runs quite warm, but not hot, you can safely touch it. Guess that's normal.

- The -18V to the DACs is present, correct and stable. I managed to measure it while the noise was present and it was fine.

- I took out SAA7030 and both TDA's from sockets, applied professional deoxidizing spray to the sockets and firmly reseated them.

- I found that +5V would not be the same voltage at all boards. This is how the voltage was different: at PSU, I could adjust via POT to exactly 5V, but already on servo board, it would be 4,95V, then on decoder board it would be 4,9V and on the Sony piggy board it would be like 4,85V. Measuring the +5V lines from PSU to the boards gave always 0 Ohm, thoug, so this was suggesting ground problems, which I confirmed by measuring resistance - it was more than 1,5 ohms. This would also confirm what I had experiences early while I was repairing the mechanism, when it had not wobble oscillator, an additional ground link to the metal frame of the drive would slightly increase reading.

So, what I did was:
I resoldered many more joints on decoder board, the little connection board for flex cables and all the joints on PSU board. I then installed a direct wire to connect ground from PSU to Servo board (excluding the original connection which goes through those little insulators (resistors?) which are installed in the metal frame between PSU and servo board "cage". I also deoxidized all cable connectors from servo board to decoder board.
Now, +5V supplies are much more similar to each others, even on Sony board it's very close, still a little lower, though.
Also, before there was a different value at pin 24 of SAA7030 (4,9V) while pin 23 had 5V, now both would have same voltage.

It plays fine. But it had also played fine before. I noticed two things, though: the red overflow LED seems to work now, it briefly flashes when you try to access a track beyond end of disc, this wouldn't happen before. Also, I haven't experienced any flicker of the green leds for tracks yet (it would happen sometimes). Otherwise, I can't tell if this has solved the noise problem, as I didn't have time to do solid testing yet.

I'll be back towards the end of January, after finally being able to test extensively, and hopefully it will be fixed. Fingers crossed.

Happy new year!
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