Page 1 of LG 3350 problems - help please

I `think` that there is a sound problem on my LG. There seems to be high frequency whistles and digital clock `mush` when playing `some` DVDs. In general, the noise stops when the disc is paused, and then comes back during the single step to the next frame. All channels have the noise.

The discs that have the `noise` are Chicken Run and Stuart Little.

The digital clock mush could be directly related to disc rotation speed - perhaps these discs are offset and the kit is working in overdrive to follow a `wiggling` track.

Can some of you guys check out your kit at `normal` listening volumes?

BTW, you do have to get close to the speaker so be careful!

As no-one is replying, I will have to do it myself :-)

> In general, the noise stops when the disc is paused, and then
> comes back during the single step to the next frame.
> All channels have the noise.

I have investigated some more. If you pause the disc, the speakers are sometimes silent, subsequent pause steps will bring up the noise and it will sometimes stay during the pause proper.

Oh yeah - I now reckon it happens on ALL discs.

Note: this ONLY happens via the Dolby Digital decoder circuitry. If you use the `normal` 2 phono outputs (via the highly rated BurrBrown D/A) the unit is totally silent when it should be.

Surely someone can do a check - sob!

Me again. I have just looked at the service manual and guess what?

The 2 channel D/A chip (PCM1716) has a zero detect output that mutes the `downstream` analogue amplifiers when `the data is continuously zero for 64K clock cycles`. The LG3350 uses this output to mute the two channel outputs.

The 6 channel D/A is the PCM1600 and has 6 zero detect outputs that should be used to mute the downstream analogue amps. The problem is that on the LG3350 circuit diagram THEY ARE NOT CONNECTED. The 6 channel outputs are not muted when they should be!

Looks like LG have skimped on the circuitry (basically not enough pins on the board to board connector is my guess), but looking at how the 2 channel mute works, 6 1K resistors can take the 2 channel mute signal (which will probably be muted when the 6 channel `should` be muted - dodgy guess?) and apply it to the 6 individual mute transistors (used only in the `absolutely everything mute` mode).

Are you guys sure that your dolby digital is quiet, as this `makes me think` that there is a design fault?

This item was edited on Sunday, 4th February 2001, 23:30

Talking to yourself? They`ll send the men in white coats.

I don`t have a 5.1 setup, but can I test this out for you using just a couple of speakers on two of the outputs?

If so, let me know exactly what I should do to try to re-create the problem.

This item was edited on Monday, 5th February 2001, 12:24

> I don`t have a 5.1 setup, but can I test this out for you
> using just a couple of speakers on two of the outputs?

Just move your existing stereo phonos to the front L+R on the 5.1 outputs. Play your favourite DVD and pause, then single step. A noise `should` `appear` after 5 or so `steps`. If not, try the rear L+R.

If yours is OK, then I may have some bad solder/components around the 5.1 D/A converter - I will send it back to dabs.

If yours is noisy .....

Thanks IT Troll.

MJJ,

I get this noise on mine as well. I`ve tried front + rear speaker outputs and it`s on both. As you say, sometimes the noise is there when paused, sometimes not, but the noise *always* starts as soon as I press `play`. That is, if I`m on pause, I can always hear the noise during the short space of time between actually pressing `play` and the time that the audio track restarts.

If the noise isn`t there on pause, it starts sooner or later when I start slow-motion, or step a few frames. The normal audio out phonos haven`t got the noise, but a slight `clicking` when stepping single frames instead.

The noise on mine has got a sort of chopping sound in it as well as the general electronic sort of noise, a bit like a helicopter.

I now see/hear what you mean. This is not good. The noise is exactly as Tim describes it and what is worse I think it is there all the time during playback! It is just that most of the time it is masked by the soundtrack.

If you monitor the rear output on an animated menu that doesn`t have any surround track you can hear the noise all the time. I have dropped a 5 second (80Kb) mp3 of what I was getting here:

http://members.tripod.co.uk/ittroll/3350noise.mp3

It sounds to me like electronic interference from the disc transport. Do you think it is worth raising this with LG?

>The normal audio out phonos haven`t got the noise, but a
>slight `clicking` when stepping single frames instead.

This is probably the hardware zero detect operating.

>The noise on mine has got a sort of chopping sound in it as
>well as the general electronic sort of noise, a bit like a helicopter

I refer to this as a digital `mush`.

As the sound changes during pause and single step, I think we are
seeing LG relying on software to mute the D/A converter rather than the
hardware - which is not used. A firmware upgrade would cure this I guess.

>and what is worse I think it is there all the time during playback

On Chicken Run, I sometimes get a high frequency hiss at the rears
when most of the sound is forward, that is what first made me aware
of the problem. Is it possible that the 5.1 encoding is at fault? Doesn`t
CR have some special enhanced 5.1 encoding?

>Do you think it is worth raising this with LG?

Yes.

Basically, I consider this a design problem and as such it can be returned at any time because it is always `unfit for purpose`.

Yep sounds like a design fault to me. Could be something simple like insufficient -+V supply rail filtering or poor routing of the D/A output traces on the PCB (high cross-talk) Either way, the `hardware mute` is a very nasty workaround (basically a brutal noise gate!) and should not be required...useful for producing spec sheets though (look at the signal to noise ratio on this!)

Makes me wonder if the main output is similarly affected...what you need is a test cd with noise recorded at about -87dB to `toggle` the bottom 2 bits, this should disable the `brutal mute` and allow you to hear if there is any other noise at higher levels (bet it`s at around -60dB!)

I could burn you a test audio CD if you want.

>"I could burn you a test audio CD if you want."

If this is a small file, send it over.

I guess if this is apparent on 3350`s on both front and rear, I should be able to duplicate it on the Aiwa.

Or perhaps the Aiwa fimware had the problem cured?
Maybe an option guys...

AIWA 370 (officially) ROCKS!!!!!!!