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-   -   Very strange fault (CD-player) (http://www.diyaudio.com/forums/digital-source/133909-very-strange-fault-cd-player.html)

jitter 27th November 2008 08:24 PM

Very strange fault (CD-player)
 
What can cause a CD-player to suddenly create white noise instead of music?

That's the problem I had (I hope) with my Primare D20. This player is about 10 years old now. It's the model with the Philips CDM12.4 mechanism (I believe the later version of the D20 had a Sony mechanism).

The problem started to appear when it was 4 or 5 years old. Once in a while the player would suddenly put a noise that can only be described as white noise on the analogue output (not on the S/PDIF output, though). It could happen 5 mins after switching on or after a hour or so. Once the white noise started, it would go on forever. The only way to get it back to normal operating condition was to power it down completely and switch it back on (it also has stand-by mode), but then it was just a matter of time before the white noise would reappear.

After a while it got so bad that I decided to have it repaired. The DAC-board (AK4324 DAC and OPA132s opamps, muting relay) was replaced and everything seemed fine...sadly only for a few months... I put it away for several years and I recently decided to try to bring it back to life myself.

Since the DAC board had already been replaced with a new item, I assumed the error had to be somewhere else, so I took out the mechanism to have access to the main board which sits beneath it. On it were some marginally soldered ICs and some (factory fitted) modifications that looked messy. I took out the pcb and took it to work where I have access to excellent rework equipment (forget Weller, go JBC). I took off some ICs and put them back on properly and tidied up some mods (esp. a resistor-mod on the SAA7xxx (I forget) which was sitting incredibly close to a capacitor and a pin)).

The player worked fine for some days, but then....the white noise came back. There was only one thing left, and that was to take out the (low cost) socket and solder a ROM IC directly on the board. The IC I'm talking about is the ROM for a 80C32 microcontroller. That seems to have done the trick, although I'm not sure yet. If the D20 keeps behaving well for a few more days, I will pronounce it repaired.

In the meantime I wonder what would have caused a DAC to spit out white noise... Any ideas???

Mooly 29th November 2008 04:37 PM

Sounds like a logic "lockup" to me. It's the sort of symptom you can create by shorting out random IC pins etc ( not something you should do unless you are extremely bored and don't mind the possible consequencies ) and the unit stays locked up until you switch off. Bit like a computer not responding etc.
As to a specific cause it could be anything !! Anything that gets hot, such as a regulator developing dry joints and "spiking" the logic is a possible, it really could be anything though. You may well have found the cause with the socket - time will tell :)

QSerraTico_Tico 29th November 2008 04:47 PM

ROM
 
I bet it's the ROM. The Sony SCD1 had a similar problem.

Steerpike 29th November 2008 08:27 PM

Quote:

There was only one thing left, and that was to take out the (low cost) socket and solder a ROM IC
It might just have been the nasty socket.
My Revox did exactly that - the problem was nothing more than dirty contacts on the D/A chip's socket. Of course there was actual audio data passing through the dirty pins in this case, which is slightly different to to your situation.

jitter 29th November 2008 09:29 PM

Thanx for the input. Right now I'm listening to music played by the D20, so it's still behaving very well! It has been playing perfectly for longer than ever since the problem appeared for the first time. I rediscovered why I had bought this player despite the fact that it was priced quite a bit higher than the max I had in mind at the time...

The theory I have now is that the serial audio data going to the DAC board at some point got so corrupted that it no longer made any sense. It was not a complete lock up of the player because it still played discs and responded to the controls af if everything was fine. If memory serves me right even the digital output still fucntioned correctly when the analogue outputs were creating white noise...

Steerpike 29th November 2008 10:18 PM

Quote:

f memory serves me right even the digital output still fucntioned correctly when the analogue outputs were creating white noise.
Exactly the same with my Revox - which is how I knew it must be the DA converter, and not any of the 'digital' ICs.
It's the same 'noise' that I get when 'playing' CD-ROM discs - as you pointed out, bits going into the DAC that don't fit the data structure that make up music.

jitter 30th November 2008 09:00 AM

Quote:

Originally posted by Steerpike


Exactly the same with my Revox - which is how I knew it must be the DA converter, and not any of the 'digital' ICs.
It's the same 'noise' that I get when 'playing' CD-ROM discs - as you pointed out, bits going into the DAC that don't fit the data structure that make up music.

In my case, it's not the DAC I was worried about. Yes, at first I thought about the DAC too, and so did the technician who replaced the DAC-board. As I wrote in the start of this topic, it did not cure the problem, though. The fact that the S/PDIF output did not suffer from the white noise problem leads me to believe that there's something in the digital audio path between the point where that signal is taken and the DAC and that it's somewhere between these two points the problem occurred.
When looking at the layout of my other CD-player (Nakamichi CD-4), it seems to me that the S/PDIF signal is NOT routed through the digital filter. Can anyone shed some light on this?

When I load a CD-ROM, the player says " NO DISC" in the display but when I press the play button it will start to play anyway. The sound I then hear does not sound the same as the white noise I experienced. Playing a CD-ROM sounds far more agressive data-pattern-like.

One thing I had not mentioned yet was that it could also start to produce white noise in stand-by mode! Apparently the D20 doesn't mute the analogue output in stand-by mode...

jitter 4th December 2008 05:44 PM

:bawling:, the white noise came back today. I'm running out of possible causes.

Everytime I tried something (meaning the disconnection and removal of the mechanism and mainboard), the white noise would stay away for a while. That's why I'm now thinking it may be caused by a connection going bad after a while.

http://i522.photobucket.com/albums/w...4313_klein.jpg
DAC-board of the Primare D20 CD-player

As you can see there is a flatcable between the DAC-board and the mainboard. The boxed headers and connectors are not gold-plated. How likely is it that this kind of connection turns bad after a while (oxidation)?

QSerraTico_Tico 4th December 2008 05:56 PM

more likely is a bad soldered SMD IC especially the signal processor.

jitter 4th December 2008 06:10 PM

Already checked and taken care off. Several ICs needed resoldering, one I even removed completely before soldering it back on the PCB. No cure though...


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