Focal fps 4160 bias adjustment

[nonprof]

Good day to all!

Please somebody give their unsolicited advice for the bias adjustment of focal 4ch fps4160. All channels has a dc out ranging from 300mv to 2v.
Do you think that i have channels that out of bias? Or there is lying problems to all channels.
Or somebody help me how to adjust the bias settings. Thanks!

 

[Perry Babin]

Bias is rarely the cause of DC offset.

If no one has any definitive information, post a photo of the entire amplifier board and another of one of the audio channels.

 

[nonprof]

Thanks perry! It works now. I cleaned all the boards with little solders. Dc offset gone to all channels.

 

[Perry Babin]

Could the problem of DC offset have been due to contamination on the board?

 

[nonprof]

Yes. There is a history of flooding wheres the amp is originated. I cleaned up the four bias boards. Intermittent protect gone, and dc output stabilize to less than 100mv

 

[nonprof]

Hi perry the problem comes back. Three channels goes bad again after I heated their bias boards. The amp is temperature sensitive, if the amp becomes warm or hot the dc offset normalizes,no turn on and off pop sound and working good but if is cold it goes to protect mode, try it multiple times then will power on.
What do you think causes the amp to have a high dc offset during the low temp?
I have pics below. Thank you!

 

[Perry Babin]

If the fixative on the base of the emitter/source resistors has become conductive, that could be part of the problem.

Post a good photo of the driver board. Read this section of the basic repair tutorial before posting.
bcae1.com - Car Amplifier Repair Tutorial - The Basics

 

[nonprof]

Hi perry! Here is the driver board.

 

[Perry Babin]

I don't recognize anything there. I thought it might be like the xtant which is extremely sensitive to temperature vs offset but I see no similarity.