Sony TA-E901 any service experience?

[Chrisr3521]

Just recapped this one and looking through the service sheets the copy I have at least doesn't have the dc balance adjustment procedure or values, does anyone have any experience with this?

Thanks

 

[JonSnell Electronic]

The Equaliser amp has the zero point set using RT401 in the shown diagramme;
The other channel is set up the same but as long as the DC offset is within a volt either way, that is acceptable as it is AC coupled.

 

[Chrisr3521]

The Equaliser amp has the zero point set using RT401 in the shown diagramme;
The other channel is set up the same but as long as the DC offset is within a volt either way, that is acceptable as it is AC coupled.

So set a close to zero with reference to ground, with as you say +/- 1v max. I take it no need to absolutely match the channels, just ballpark of each other?

 

[Chrisr3521]

New problem with this, when testing it sounds noise than it should, almost like a quiet motorboating. I've scoped the power rails and this is the negative 18v rail from a 7918 regulator, I take it has gone noisey?
2021-01-22_03-35-01 | chris reddish | Flickr

 

[U230421]

If the 7918 has become noisy (or an electrolyte on it's rails or reference), it can seep through to the signal path. The motorboating is the very clue. Easy & cheap replacement or both the 7918 and surrounding caps - might be the fix!

 

[Chrisr3521]

So changed the regs over and no joy still hiss, quiet motorboat through both channels, so I'm assuming power supply or ground issue? Where to look next?

 

[Chrisr3521]

So voltages from the psu,

18v supply -17.576, +17.576
5v supply -4.926, +4.927
24v supply -23.160, 23.419

+24v seems a tad low to me?

 

[Chrisr3521]

So some measurements of ripple came across this on the NE5534P pin 6, is something wrong here or is this normal behaviour?

 

[anatech]

Check to make sure your reference is clean. If D504 has failed it might do what you are seeing. Try replacing the 10 uF caps across the reference with Poly-Aluminium types. If the negative supply is oscillating, the positive supply will pick it up. It is possible the NE5534 has gone bad, but that has nothing to do with the recap.

-Chris

 

[Chrisr3521]

The reference looks clean, measured all around. Ripple (seems to be 360mv peak 2 peak) is present until the diode end of r509/512 I've attached the noise from the emitters of q501/503. Anywhere else I should be measuring? I take it this could account for the noise on the output?

 

[anatech]

360 mV is huge!

Maybe your ground point is wrong, or your 'scope is very noisy. But if those are clean, looks lie a bad 5534, and they are pretty quiet. Cheap too. Try putting in a new one.

 

[Chrisr3521]

360 mV is huge!

Maybe your ground point is wrong, or your 'scope is very noisy. But if those are clean, looks lie a bad 5534, and they are pretty quiet. Cheap too. Try putting in a new one.

Well, tried new 5534's and still the same. Ground point wise I'm using the main psu ground and my scope is a Rigol 1054z, decent but not ground-breaking.

360mv is measured throughout most of the psu from the from the bridge onwards, but when the voltage goes to different parts of the circuit it seems to be unmeasurable.

Maybe I'm measuring the reference in the wrong place?

Anywhere else to look for the source of the noise on both outputs?

 

[anatech]

Honestly, it looks like they are trying to supply an extremely low noise supply. Your readings are, for whatever reason, completely useless. You need an analogue scope to see what is going on for real. All we can do is guess. I think your scope is lying to us.

All right. Is the noise on all inputs, or just phono? Do you have shorting plugs in the phono inputs?

-Chris

 

[Chrisr3521]

Honestly, it looks like they are trying to supply an extremely low noise supply. Your readings are, for whatever reason, completely useless. You need an analogue scope to see what is going on for real. All we can do is guess. I think your scope is lying to us.

I can get access to an analogue scope next week, readings wise, measure the ripple again?

All right. Is the noise on all inputs, or just phono? Do you have shorting plugs in the phono inputs?

Noise is on all inputs that's why I thought psu as common to both, and no shorting plugs in the phono