Phase Linear 2000 troubleshooting

[laatsch55]

Well, I replaced Q2, and I have no more Buzz but a light hum is still hearable ...

60hz hum?

 

[Coldsmoke]

60hz hum?

Yes it's a 50Hz thing. Can't figure why :/

 

[Coldsmoke]

60hz hum?

And, I haven't replaced the IC's by the ones you sent me on yet

 

[NavLinear]

One simple check is to verify that all components are plugged into the same AC circuit. It is possible that differences in AC potential can develop between grounds of different circuits resulting in a current differential between the grounds. This can cause voltage drops across the ground wires in the power cords of the circuits that provide power to the audio components and this has the potential to create the line frequency hum.

 

[laatsch55]

Yes it's a 50Hz thing. Can't figure why :/

Ah yes Europe....the 50hz hummers...

Have all the electrolytics been replaced?

 

[Coldsmoke]

One simple check is to verify that all components are plugged into the same AC circuit. It is possible that differences in AC potential can develop between grounds of different circuits resulting in a current differential between the grounds. This can cause voltage drops across the ground wires in the power cords of the circuits that provide power to the audio components and this has the potential to create the line frequency hum.

I don't have a ground wire nav

 

[NavLinear]

I don't have a ground wire nav

The AC neutral line eventually ties to ground. It's a quick and easy test by using the same AC circuit for the preamp, amp and source.

 

[gadget73]

They don't have neutral wires over there either. 220v, both are hot.

I suppose there is a possibility of inverted phase on the power wiring though. Not sure if the cords can be flipped over, but that might be worth a try.

 

[Gepetto]

An other consideration, I noticed that I had to use quite high resistors values to lower the LED brightness (about 300k), can this affect the functioning of the TIS97?

The TIS97 in that circuit is just a poor man's zener diode. Why PL did that I will never know.

The high value is right, the LED you have is an ultrabright and you do not want an ultrabright in that application.

 

[Coldsmoke]

The TIS97 in that circuit is just a poor man's zener diode. Why PL did that I will never know.

The high value is right, the LED you have is an ultrabright and you do not want an ultrabright in that application.

It's troubling indeed....

Well, I finally checked the values of the new caps that have been replaced by the previous owner, I can't figure out why but C42 and C43 where downsized from 10/50 to 1/100 (???) and C47-48-49-50 where also downsized from 22/35 to 2.2/50.
I suppose it is worth to change again these caps and that it could help with the hum thing... right?

 

[NavLinear]

They don't have neutral wires over there either. 220v, both are hot.

I suppose there is a possibility of inverted phase on the power wiring though. Not sure if the cords can be flipped over, but that might be worth a try.

http://en.wikipedia.org/wiki/Ground_and_neutral

 

[Coldsmoke]

http://en.wikipedia.org/wiki/Ground_and_neutral

I think I'll give a try to the neutral/phase check once I'll have replaced the electrolytics

 

[Gepetto]

It's troubling indeed....

Well, I finally checked the values of the new caps that have been replaced by the previous owner, I can't figure out why but C42 and C43 where downsized from 10/50 to 1/100 (???) and C47-48-49-50 where also downsized from 22/35 to 2.2/50.
I suppose it is worth to change again these caps and that it could help with the hum thing... right?

Likely will not fix your hum but it will improve your low end frequency response. The P.O. did not do the right thing by this preamp. What did the P.O. do to the values of C40 and 41?

My suspicion is that there is a ground loop inside the PL2000 because of the multiple DC ground tie points to the chassis. Never a good thing.

 

[Gepetto]

Likely will not fix your hum but it will improve your low end frequency response. The P.O. did not do the right thing by this preamp. What did the P.O. do to the values of C40 and 41?

My suspicion is that there is a ground loop inside the PL2000 because of the multiple DC ground tie points to the chassis. Never a good thing.

I looked over the artwork in the service manual and it pretty much confirmed my thoughts. None of the OUTPUT RCA jacks have an attachment to DC ground. Rather they rely on a connection to the chassis for the ground reference. This is a possibility for your low level hum problem.

 

[laatsch55]

And maybe many others....

 

[Coldsmoke]

And maybe many others....

Ah ah, hope not... The P.O. kept the same values for C40 and C41.
Once I'll have changed - again - the caps, everything aside the ceramic capacitors will have been changed. I hope I'll get some result ...
Joe, is there something I can do to improve the DC grouding?

 

[Coldsmoke]

Perhaps can I install some jumpers to the DC ground?

 

[Gepetto]

Perhaps can I install some jumpers to the DC ground?

We will see what we can do to recommend some improvements. Be patient though...

 

[Coldsmoke]

We will see what we can do to recommend some improvements. Be patient though...

Will be : )

 

[laatsch55]

I am sending Joe one of my 2000's so he can peruse the situation up close and personal....that's what he meant by being patient. It will be headed his way Monday..