Output level of Sony cdp-395

[ytsoc]

Hello ,
I got this player and the output seemed kinda low.
So i put a 1khz tone on a cd and i measured 0.7v peak to peak output.
Is this normal? The specs say it has 2 volts output .
I removed all circuits after the buffer stage and the results are the same, replaced op-amps , nothing changed.
I don't know what else could be at fault that is common to both chanels
I do have an osciloscope .
Here is the output stage:

 

[DF96]

Problem with the muting circuit?

 

[Mooly]

It depends what level the tone is on the CD

A 0db tone should be playing back at around 5 to 6 volts peak to peak. Check the calibaration of your scope too.

I doubt you have a real fault with the player.

 

[ytsoc]

Problem with the muting circuit?

removed everything after the buffer output(even the output caps)

It depends what level the tone is on the CD

A 0db tone should be playing back at around 5 to 6 volts peak to peak. Check the calibaration of your scope too.

I doubt you have a real fault with the player.

test tone is indeed at 0db, scope is ok(but even if it was faulty , compared with a technics tuner, and pc , the cd-player sounds a lot weaker)

 

[Mooly]

Have a look at the signal with the scope on the output of the first two opamps (the TL082's). That should be the same amplitude as you would get at the final output sockets.

If it really is a 0db tone then that suggests a problem somewhere but I find that hard to believe I've never ever once had a low amplitude problem from any player. If the player has an unknown history or hasbeen worked on then check that BOTH feeds to the differential amps are present. That is the signal on those two red arrows going to each opamp. A normal music CD should have peaks approaching 2.5 volts (5 volts peak to peak). Try it.

 

[Mooly]

It just so happens I have a similar-ish player on the bench at the moment,
http://www.diyaudio.com/forums/digital-source/226288-sony-cdp790-kss240-restoration-project.html

and so I know what the levels should be. The 2 volts you quote will be 2 volts RMS (a kind of standard for many players) which is 5.66 volts peak to peak at 0db.

 

[ytsoc]

output voltage p-p at output pin of first op-amp is about 1.5v then after R369 drops to 0.7volts.

Here are some scope shots:
inverting input of first op amp:

non inverting input of same op amp

output of first op amp(1.5V)

input/output of buffer(second op amp)

 

[Mooly]

That doesn't look right. The output of the first opamp looks incredibly noisy.

Let me just look at mine... 5 minutes

 

[Mooly]

OK. The output of the first opamp on mine is around 5.8 volts peak to peak. It looks absolutely clean and clear.

The signals on the two input pins of the first opamp also look clean and clear and are around 1.2 volts peak to peak.

If you want pictures it will have to wait 'till tomorrow but they are just a perfect clean and clear sinewave.

 

[ytsoc]

welp, since up to the input pins of first op amps we only have passives can i assume that the DAC is toasted?

 

[Mooly]

Maybe but I've never had one fail. If there's nothing obviously amiss physically then I guess it has to be suspect. Big chips are always always the last to suspect though, 99% of the time its something else... but there's always a first time.

Only you know the history of the player. Check the supplies are OK on the DAC. Go round all the pins on the DAC with the scope and a meter looking for anything out of the ordinary or unexpected. If nothing is found then it has to be suspect.

 

[simon7000]

welp, since up to the input pins of first op amps we only have passives can i assume that the DAC is toasted?

No. I would look at the DAC and see where it gets the reference voltage. It looks like it actually is doing the digital part but the output is low on both channels. So the reference and the power supply to the DAC should be checked.

Cross posted with Mooly

 

[ytsoc]

i don't know anything about the history of the player, at first glance every ps rail is ok except for a +10v one that is +12v

No. I would look at the DAC and see where it gets the reference voltage. It looks like it actually is doing the digital part but the output is low on both channels. So the reference and the power supply to the DAC should be checked.

Cross posted with Mooly

good one, i did not know how dacs work.
I will check for this, thank you

 

[Mooly]

See what you find, don't overlook ANYTHING Go round every pin with the scope, even the grounds. Yes it may well be duff but don't assume it is.

I'll have to leave it for tonight

 

[ytsoc]

thank you all for your help, i'll do some checking around the DAC and report my findings here in a couple of hours

 

[ytsoc]

i did some measurements.
The one that worries me most is that on the digital filter, but it's a bit odd as the pin is connected to the dac via a 1.2k resistor and there are 2 diffrent values on each side of that resistor on the schematic.
Here are the values:
Digital filter

DAC

 

[Mooly]

The reading I get (mine is a different filter but same DAC) are,

R319, 2.5 volts in stop and play
R318, 1.06 volts in stop and 1.87 in play
R316, 2.8 volts in stop and play

Essentially same volts on each end of resistor.

 

[ytsoc]

well i guess it's a dead end. I'll do some more measurements but i don;t think i'll find anything else wrong

 

[Mooly]

It is a strange one I must admit. There's not much else you can do really having been all around the IC's. When your sure everything else is OK then its time too look at swapping the IC's.

 

[ytsoc]

at the moment it's more of a curiosity than a need to repair it, most probably i'll sell the transport along with the laser and keep the case for some diy amp