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Old 4th December 2008, 10:30 PM   #11
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The plug that crimps onto the ribbon cable (IDC connector) - they can lose contact with the ribbon cable where they are supposed to pierce the ribbon's insulation.
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Old 5th December 2008, 05:14 AM   #12
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Well, I think I'm going to replace the whole thing with seperate strands that I solder directly onto those boards.

I might even use thin coax cables because I noticed the flatcable picks up some hum when I turn up the volume on the amp to the max. If I wrap some aluminium foil around the flatcable, the hum is nearly gone...
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Old 5th December 2008, 06:20 AM   #13
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Have you checked the PSU for DJ's yet ?
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Old 5th December 2008, 03:48 PM   #14
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What do you mean by DJ's? Dry joints?
If so, yes PSU is fine.

Digital and analogue circuits in the D20 have separate PSUs, starting with two transformers. The DAC-board has its own PSUs (it gets AC power from the transformers), again digital and analogue are separated.

One of the first things I did was measure the PSUs and the oscillator. All are rock steady.
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Old 5th December 2008, 04:21 PM   #15
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Dry joints yes It sounds a tricky one this. By their very nature "digital" faults once they occur don't usually go back to normal again unless the logic is reset by powering off which makes fault finding all the more difficult.
It's usually things that run hot that suffer with DJ's but not always. If the transformers are PCB mounted it's worth running an iron over them. Any fuse holders ? When you do find it you will kick yourself, the evidence will have been there all along.
If you suspect an IC try a hairdryer on it to heat it up while it's on. Give everything a good poke, again while it is on.
Good luck
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Old 5th December 2008, 09:20 PM   #16
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Quote:
Originally posted by Mooly

It's usually things that run hot that suffer with DJ's but not always. If the transformers are PCB mounted it's worth running an iron over them.


They are and I resoldered them today, just to make sure.

Quote:
Any fuse holders ? When you do find it you will kick yourself, the evidence will have been there all along.
Only one in the primary side, the others (SMD) are soldered directly onto the mainboard.

Quote:
If you suspect an IC try a hairdryer on it to heat it up while it's on. Give everything a good poke, again while it is on.
Good luck
That will only be possible with ICs on the DAC-board. The ICs on the mainboard are almost completely hidden below the mechanism. I don't suspect any of them though.

This evening I replaced the ribbon cable by bits of standard (shielded) interlink cable. It was a time consuming and fiddly mod, and the only thing to do now is listen to music and be patient...

EDIT: This time I didn't have to wait for very long...it's spitting out white noise again...
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Old 6th December 2008, 06:17 AM   #17
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Try extremely small amounts of freezer spray on any suspect IC with it working. I say that because once it does it's fault there is a good chance that even if the IC was playing up it would have "confused" the logic and blasting it with freezer may not correct it. The idea is to see if you can keep it from going faulty. Just drip freezer onto the part every minute or two.
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Old 6th December 2008, 01:35 PM   #18
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Well, the freeze spray (FS) is something I hadn't considered yet, even though at work I sometimes use it too for finding a fault. It's something I can't try yet though, I have no FS handy...

I kept myself busy with the D20 anyway. It's a nicely designed CD-player with one exception: the PCB-mounted transformers. From the very beginning I had plans to move them off-PCB because they put out a loud mechanical hum which the 2 mm thick steel housing only seems to amplify (resonance frequency?). Despite this, the D20 has always been a very musical player. Whatever I play, I can't stop tapping my feet, with the exception of the many "loudness war" CDs record companies are putting out nowadays.

This mod might sound a little off topic, but yesterday the white noise came back far more rapidly than usual after trying something. This morning I found out that I hadn't tightened the screw that sits between the (digital) transformer and the two elcos. That got me thinking: what if the vibrations have something to do with the white noise fault??? Only one way to find out: apply the mod I always wanted to do, but somehow never did, until now.

Click the image to open in full size.
As you can see, the mechanical hum has been taken care of. The transformers now sit upside down on some soft rubber rings. The D20 is no longer a "hummingbird".
I also reverted to the ribbon cable between the DAC-board and the mainboard. Three reasons: it was not the cause of the white noise, the D20 sounded more clinical with the interlink-wiring and it looks far less messy this way.
The hum in the analogue signal (in the noise floor) at very high volume levels has also been reduced to nearly nothing by the longer distance between the DAC-board and the transformers.

But will the white noise problem come back or not? Time will tell...
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Old 6th December 2008, 01:47 PM   #19
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Definitely not physical ? Poking and bending the PCB's has no effect at all does it ?
Very strange fault. In all the years I worked on CD players I have vague recollections of only one ROM failure, I don't think it was intermittant though. Must be nearly 20 years ago now
LSI chips are usually supremely reliable. You will have to see.
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Old 6th December 2008, 02:48 PM   #20
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In 8+ years I've had my share of bad connections, esp. in multilayer PCBs, although it's not a common phenomenon. Cracked ceramic capacitors can sometimes also be found by bending or pressing.
So yes, I applied the trick while the D20 was playing, it doesn't seem to affect it though.

While removing the transformers I seriously stressed the main PCB. Lets just say that they were hell to remove, but I managed without any (serious) damage. If there is/was an intermittent contact, it may have been repaired in the process for now or forever (preferably the latter).

I'm not thinking the ROM was the cause anymore. The D20 is operable when the white noise appears and yesterday I confirmed that the S/DIF output was working fine while at the same time the analogue output was nothing but white noise.

Contrary to what I wrote, the boxed headers for the ribbon cable are gold-plated.
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