Gibsonian's Cherry Pl 700 Ser I, soon to be a PLWO-1000

[laatsch55]

Here ya go....

 

[Gepetto]

If I am understanding your post correctly Lee, when left channel bias is set to minimum, you achieve an offset of 0.004V but when you turn the bias up to maximum, you get an output offset ranging from +16 to +25VDC and then it slowly drifts down.

Did I get that correctly?

 

[laatsch55]

try this one..

 

[laatsch55]

If I am understanding your post correctly Lee, when left channel bias is set to minimum, you achieve an offset of 0.004V but when you turn the bias up to maximum, you get an output offset ranging from +16 to +25VDC and then it slowly drifts down.

Did I get that correctly?

Correct.

 

[Gepetto]

OK that is twice I have gotten dumped by Phoenix this morning. Is something in process, like a backup?

 

[Gepetto]

Frustrating to write a long response and then have the website dump you when you hit submit response.

 

[laatsch55]

Also, the right side will not go below 357MV and adjusting it makes the offset on that channel go bonkers, from Minus 15 mv to minus 89 mv.

 

[Gepetto]

The value of R37 at the bottom of the negative stack should be checked Lee. It looks like the first band is RED which is not right but that could just be the camera. Should be between 150 and 180 ohms. Looks like a replacement resistor.

 

[laatsch55]

Frustrating to write a long response and then have the website dump you when you hit submit response.

VERY!!

 

[Gepetto]

The normal offset ranges from -0.009 to -0.011V

 

[laatsch55]

On Series I's they were 150, and this one measures 150.2

 

[Gepetto]

The second observation is what is that small orange or tan resistor looking item halfway up that same stack going from the output driver base bus wire to the junction of all the 0.27 ohm emitter resistors? Is that a replacement R39?

 

[Gepetto]

Are your sockets any good and are the transistor leads actually making contact? Prior insertion of larger leaded devices followed by smaller ones renders these sockets very unreliable. Carefully squeezing the tulip contacts will usually restore that.

This is one of the weakest parts of the PL assembly, the cheap sockets they used.

 

[Gepetto]

Something wrong with your right channel as well Lee if it is doing that kind of stuff. Just not as bad as the left channel.

Bottom line, based on what you have told me, the negative half of the output bridge is not coming into play here and needs to.

 

[Gepetto]

going out for a while. back later.

 

[laatsch55]

The second observation is what is that small orange or tan resistor looking item halfway up that same stack going from the output driver base bus wire to the junction of all the 0.27 ohm emitter resistors? Is that a replacement R39?

Yes a one watt Dale.

 

[laatsch55]

I'll scope it and see what a sinewave looks like.

 

[laatsch55]

Joe, up until the point that adjusting the bias throws BIG DC to the rails the output sinewave looks very good.

 

[jbeckva]

OK that is twice I have gotten dumped by Phoenix this morning. Is something in process, like a backup?

No nothing going on

 

[laatsch55]

Gotta go to work myself.