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Luxman L-100 faulty channel

I see no obvious faults on the PB-640 here
 

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Note to self to reread section 9 on the touch mute. Is it saying that the circuit is designed to hum but through the use of high gain transistors the hum is at a very low level. So what happens at refurb when the transistors are replaced with lower gain items???

Anybody find the attenuate control VR601cd on the schematic, having a blonde moment...
 
mbz said:
Note to self to reread section 9 on the touch mute. Is it saying that the circuit is designed to hum but through the use of high gain transistors the hum is at a very low level. So what happens at refurb when the transistors are replaced with lower gain items???

Anybody find the attenuate control VR601cd on the schematic, having a blonde moment...
Click to expand...
Maybe there’s an error in the manual this is where I think it would be? Looks like it lists the balance control twice instead ?
 

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I replaced the mute circuit relay but the hum prevails both with speakers and headphones any ideas where I can look next?
 
The schematic is not an easy read. Tried looking for what "components" the attenuator controls then having a closer look at those components/solder joints/replace. I need to revisit that touch muting, check/try with it turned off/can it be turned off? Same behaviour with off?
 
mbz said:
The schematic is not an easy read. Tried looking for what "components" the attenuator controls then having a closer look at those components/solder joints/replace. I need to revisit that touch muting, check/try with it turned off/can it be turned off? Same behaviour with off?
Click to expand...
There’s a switch on the rear that you can turn it off and on, I have it set to off already. I have another l100 working which I plan to swap the power supply board over to rule it out also
 
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Ok good news I think I’ve solved the hum problem - take note future or current l100 owners who encounter this problem

I swapped pb-647 I had initially no difference then I thought I should check the voltage adjustments to the power supply given the swap over I noticed once you exceed 59v the hum exists reducing it back to 58v the hum disappears

With the wood sleeve I notice both units hum the same way

Interestingly on one of my Luxman the lowest I can get is -58.6v and +58v the other I can dial in +-58v with ease but still hummed a little, reducing it to +-56.9v removed the hum

Will do some listen tests and see how it goes but feeling good so far!
 
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