Newly assemble pl14 rev G bias trimmers do not work correctly

C

CrazyIvan

New Around These Parts
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Mar 27, 2022
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Hello, I recently added the DC protection, then new power caps from WO. I just assembled the pl14 rev G board. Started on a DBT no issues. went to adjust bias and my DMM readings are -.019 DC on both sides. Bias trimmers turned full CCW to start. Turning CW has no effect on the DMM. I am using board test points and white and red speaker outputs as test points. If I read between white and black or white and red I get .003 VDC. It doesn't seem normal to not get any bias adjustment. Any help is appreciated.
 
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Make sure the storage cap polarity is correct and you left the correct components off the control board for your quasi complement or full complement back wall.
If all is correct then post many good hi resolution photos.
 
Also check your rail voltages. With meter set to VDC, connect your negative lead to the copper bar. Touch positive lead to the other upper storage cap screw with the wired connection, should be around +80 VDC on a 400, +100 VDC on a 700. Now touch that same positive lead to the lower cap screw with the wired connection, -80 VDC, or -100 VDC depending on amp model.
 
I left the correct components off for full comp. I will go check voltage as you suggest, The voltage test points on the board read the correct -/+ 15 VDC, I will get photos soon.
 
CrazyIvan said:
Hello, I recently added the DC protection, then new power caps from WO. I just assembled the pl14 rev G board. Started on a DBT no issues. went to adjust bias and my DMM readings are -.019 DC on both sides. Bias trimmers turned full CCW to start. Turning CW has no effect on the DMM. I am using board test points and white and red speaker outputs as test points. If I read between white and black or white and red I get .003 VDC. It doesn't seem normal to not get any bias adjustment. Any help is appreciated.
Click to expand...


Just for shits and giggles, try the stock bias test point, each side of the 10 ohm resistor on the back wall....there are 4 of them, one for each column of outputs. The ones you are concerned about are the column closest to the transformer and the 3rd from the transformer.
 
Dig the PS cap hold down bushings. Is the PS cap polarity correct, I see a + where it shouldn't be if that + is attributable to the closest post...
 
laatsch55 said:
Dig the PS cap hold down bushings. Is the PS cap polarity correct, I see a + where it shouldn't be if that + is attributable to the closest post...
Click to expand...
Those bushings are the standard White Oak Audio offering for the old 4 fin amps Lee. Saves drilling any holes in the chassis.
 
Sorry to sound dumb, are the rail fuses the screw in fuses on the back? I never removed those. The amp was working after the DC and cap install. Does the copper bus bar between the large caps connect the caps + on bottom cap to - on top cap? I replaced the new ones the same direction the old ones came out. I did cut off the other white wire and remove from PAD5R. See pics, still -.019 on the test points. No trimmer adjustment.cap polarity 2.jpgcap polarity.jpgcut off bus wire and removed white wire after pic.jpgmoved white wire.jpg
 
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