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PAS 3 Hum
PAS 3 Hum
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Old 12th June 2018, 11:18 PM   #11
Conrad Hoffman is offline Conrad Hoffman  United States
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Location: Canandaigua, NY USA
Do you have the same amount of hum in both channels?
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Old 12th June 2018, 11:27 PM   #12
rayma is online now rayma  United States
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Quote:
Originally Posted by Marksd View Post
it was working great before the electrolytic started failing with the old boards.
The capacitor you have is fine. The original power supply design works well enough.
There is a problem somewhere.

Can you put these steps in the right order of what you did?

replace old capcitor
replace phono board
replace line board
replace filament supply
hum started
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Old 13th June 2018, 12:24 PM   #13
Marksd is offline Marksd  United States
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The hum was audible before I replaced the electrolytic can and was dead quiet with the typical heater hiss at a volume setting of 2:00 o'clock, which is to high volume for me to listen too. I replaced the PC5 and PC6 boards and the definition from the line inputs is dead quiet and very transparent. The music is better then they ever have been. When any of the phono, tape or special is selected there is a hum that is consistent in both channels and I can increase the volume, which increases the hum. The hum is amplified by the line PC5 board. If I use shorting plugs on tape amp it kills the hum but also kills the sound to that channel. I have gone component by component checking values and all are in spec. I rewired he unit exactly as shown in the manual pictorials. the only thing I can think of is that the gain is so high in the phono stage that it is picking up this hum somewhere. I even tried tube shields on the phono PC6 board to no avail. I do not have an oscilloscope to check where the hum is being injected into the phono circuit.
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Old 13th June 2018, 12:26 PM   #14
Marksd is offline Marksd  United States
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replace filament supply
No Hum
Hum started
replace old capacitor (hum went away)
replace phono board
replace line board
Hum is back
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Old 13th June 2018, 12:27 PM   #15
Marksd is offline Marksd  United States
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Conrad, hum is exactly the same in both channels. and increased as I increase volume but only when on the phono, special and tape input on the selector switch only.
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Old 13th June 2018, 12:39 PM   #16
kstagger is offline kstagger  United States
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Underside shot? Everything grounds at the cap cap twist-lock that contacts the metal chassis - that's where I would be looking first. You could run another ground wire from the phono board to the capacitor grounding point.
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Old 13th June 2018, 02:16 PM   #17
rayma is online now rayma  United States
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Quote:
Originally Posted by kstagger View Post
You could run another ground wire from the phono board to the capacitor grounding point.
There should be two ground wires to the can from the phono pcb already.
Post close photos of the bottom wiring.

Last edited by rayma; 13th June 2018 at 02:23 PM.
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Old 15th June 2018, 12:20 PM   #18
Marksd is offline Marksd  United States
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All, yes there are two grounding wires from the PC6 to the can. I read where a person tied the two grounds together and then connected eyelet 10 the to can. I am very careful to make sure things are the same. I have included pictures of the bottom of the chassis. The capacitors on the bottom side are to block DC from the outputs as used in the pas 3x.
Attached Images
File Type: jpg DSCN5372.jpg (304.6 KB, 53 views)
File Type: jpg DSCN5373.jpg (303.6 KB, 53 views)
File Type: jpg DSCN5362.jpg (375.8 KB, 51 views)
File Type: jpg DSCN5366.jpg (354.6 KB, 51 views)
File Type: jpg DSCN5365.jpg (378.2 KB, 50 views)
File Type: jpg DSCN5368.jpg (251.8 KB, 14 views)
File Type: jpg DSCN5363.jpg (331.0 KB, 14 views)
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Old 15th June 2018, 03:21 PM   #19
rayma is online now rayma  United States
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Quote:
Originally Posted by Marksd View Post
I am very careful to make sure things are the same.
Looks about normal. Are the can capacitor's mounting lugs twisted to lock it tightly to the chassis?

Last edited by rayma; 15th June 2018 at 03:27 PM.
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Old 15th June 2018, 06:09 PM   #20
Marksd is offline Marksd  United States
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Yes the can is tight. I checked it and even twisted the lugs more.
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