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Old 24th December 2008, 10:29 AM   #31
jitter is offline jitter  Netherlands
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I was just in another room when I heard white noise coming from the living room and I thought "OH NO, NOT AGAIN!" , but then I heard the white noise fade out and music fade in...
I am listening to the album "All Things Must Pass" from George Harrison (2001 rerelease). Track 12 of the 2nd disc ("I Remember Jeep") starts with a white noise sound effect that was not unlike (bit whiter, though) what the D20 used to do when it went bad.
Geez, that had me jump up for a second...
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Old 24th December 2008, 11:09 AM   #32
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Oh I know how that feels Used to happen with TV's, you fixed a fault, you are sure it's OK, you delivered it back and switch on -- fault still there --phew, no it's "them" transmitting some odd program
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Old 13th November 2010, 08:46 PM   #33
jitter is offline jitter  Netherlands
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I'm sad to report that the white noise problem has reappeared. Perhaps I was looking in the wrong direction all this time, but maybe I found the actual cause by chance today. Maybe... high potential on chassis CD-player
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Old 21st November 2010, 08:26 AM   #34
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This white noise problem keeps me puzzled. After connecting the CD-player to PE the problem went away...for a while. It came back big time today and kept reappearing a short time after each of several resets.

In the past the analogue output would just start to make white noise, but now it's accompanied by a buzzing sound which has a lot in common with that of an electric arc sound-effect in many a Hollywood production... It cuts in and out when the analogue output is producing white noise (presumably and upset DAC).
Now that this buzzing keeps cutting in and out more often and for longer periods have I finally something to trace...

There's definitely an intermittent failure going on here that seems to progress, albeit very slowly (just have a look at when I started this thread). Now that it keeps reoccurring rather rapidly can I hook up a scope to the PSUs of the analogue pcb and wait. Perhaps a bridge rectifier is failing...
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Old 21st November 2010, 02:50 PM   #35
jitter is offline jitter  Netherlands
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Finally found something.

The DAC-board is powered by four voltage regulators. An LM317/LM337 combo for the analogue circuits and two LM317s for the DAC (one for digital and the other for the analogue section).

It's the PSU for the analogue section of the DAC that seems to go wrong intermittently.
The LM317 is fed through a 22R0 resistor (just like the other one). Across it is 1.075 V, so I calculated a current of 49 mA. When the fault occurs, Vin of the LM317 drops below 8 V (it's set to 5 V Vout). It drops to ca. 7.6 V, and that's probably not enough to keep it in regulation. I assume this leads to an unstable 5 V which upsets the DAC.

It only lasts a short time before the fault somehow corrects itself, but this time it was long enough to see Vin drop far below the normal 8.1 - 8.2 V. I wasn't able to measure the voltage drop across the 22R0 resistor in time to see if the drop was caused by an increased current draw. Neither had I time to measure if the voltage on the other side of the resistor remained steady.

Now I know why the DAC gets upset, it's time to trace the real cause. In other words, up- or downstream the LM317. I'll replace the LM317 tomorrow to rule that out. I must do that at work as it's an SO8 we're talking about, and I don't have desoldering equipment for SMD at home.
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Old 21st November 2010, 10:15 PM   #36
jitter is offline jitter  Netherlands
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Default Found it?

Believe it or not, but after several years of chasing ghosts, I might finally have found the cause of the white noise problem!

When it happened again, I saw the voltage drop on Vin while at the same time the voltage across the 22R0 resistors stayed the same. In other words: no change in load but in voltage supplied to the VRs.

It seems that one of the pins of the pcb-transformer for the analogue circuits isn't making contact with the windings properly. It's a 4x 7.5 V transformer of which 1x 7.5 V is used seperately for the DAC and the remaining three in series for the analogue power supply. Repair of the transformer itself is impossible, it is a pcb-type which is sealed with resin.

It's the winding that feeds both VRs for the DAC that seems to make intermittent contact. I found out by chance when I touched the wires (transformers were originally pcb-mounted, see earlier in this thread). Then I measured the several windings and found that one of them varied with pressure applied to the pins. This most likely also happened when in normal use as a result of expanding/shrinking due to heating/cooling. When that voltage dropped below the threshold of the VRs min Vin, that would have led to no regulation and as a result a DAC that would start spit out white noise until a reset.

To make absolutely sure, I will supply power the DAC from an external PSU and see what happens...
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Old 23rd November 2010, 08:03 PM   #37
jitter is offline jitter  Netherlands
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Smile FINALLY FIXED!

Quote:
Originally Posted by Mooly View Post
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
I finally fixed the D20 by adding a transformer from a scrapped pcb I took home from work.
After a night on the lab PSU it kept working flawlessly, so I decided to finalize the repair. Going through the scrapped pcbs I was lucky to find one with suitable voltage. The somewhat higher voltage of this transfo meant upgrading one elco on the analogue pcb to a higher voltage (was 10 V). Luckily I had one of the same capacity and lead spacing of 35 V lying around.

I quoted Mooly's first reply as the combination of logic lockup caused by a faulty power supply was indeed the case (albeit caused by a somewhat less common fault). Finally fixed...
Attached Images
File Type: jpg D20 after repair.jpg (204.8 KB, 76 views)
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Old 4th December 2012, 05:43 PM   #38
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Default Another very strange fault

By both a CD-100 from Thule Audio and a D20 from Primare I observe, that the tray goes several times in and out and then only in one direction without stop.
Therefore I have start a new thread:
http://www.diyaudio.com/forums/digit...ml#post3270416

Last edited by tiefbassuebertr; 4th December 2012 at 06:08 PM.
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