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Luxman L-100 woes

SingleReel

SingleReel

Member
I have owned this Luxman L-100U for about two years now and it seems this unit has been nothing but constant trouble. I know it was serviced before I purchased it and it immediately had problems. I decided to have it serviced by a long time professional and he claimed the last Tech did him no favors. Upon getting the amp back I was never really satisfied with the noise level it had, but I lived with it. Few months later I had a channel go dead, I decided to give it a look myself, it turned out to be a diode in one of the power amp sections. I was not impressed with the quality of repair the tech last did, just sloppy work. About half a year later, one day I turn on the L-100 and the left channel had now acquired a significant amount of noise.

The left channel noise is unaffected by the volume and source. There is no distortion noticeable in the audio. I decided to see if I could find the cause of the new noise issue. Currently I'm at my witts end, I have not been able to find the source of the noise and it seems the more I get into this the less it makes sense. I'm now familiar with how difficult this model is to service. It has been weeks and I'm stumped. Any help would be greatly appreciated. Here are my, observations, findings, and newly serviced components...

Observations/findings:

Significant noise issue is in the left channel output.

The noise appears after the 'Main in' section.

The left channel does not have the noise when coming directly out of the left Power amp section (PB-649). (Although the right does have noticable noise directly out of the right power section? Odd.) This stays the same after leaving the relay (directly after power amp section).

After leaving the relay, both audio channels follow a wire to the speaker switch, where oddly enough the significant noise issue then presents in the Left channel and the right becomes relatively clean... as if the opposite of after the relay? (I removed the wires from the speaker switch and no change).

One other odd observation is when I swap the signal inputs to the Left and Right power amp sections (PB-649), the noise follows the swap (presents in whichever power amp section has the left channel signal input). This is odd to me because all that is prior to the power amp signal input is, a relay, attenuator and 5 resistors per channel, which I have checked and replaced all with metal film.
Additionally, just swapping both the entire power amp sections do not change the noise, it remains on the same channel.

Serviced/replaced components:

Prior to the current noise issue;
(bias and offset set correctly)

Power Supply PB-647:
Electrolytic Capacitors
All 2sc1345 with BC550CTA

Power amp boards PB-649:
All Electrolytic capacitors
All output TO3 transistors
All 1N4003 diodes
All VD1221 diodes

After noise issue:
(Cleaned all pins and contacts)

Power Supply PB-647:
All Resistors in audio path with Metal Film
Audio path (c913&c914) Mylar capacitor with Film cap.
Resistor r933 with 2 watt.

Equalizer PB-636:
All Electrolytic capacitors
All 2sc1345 with BC550CTA
All VD1221 diodes

Tone Amp PB-639:
All electrolytic capacitors
All 2sc1345 with BC550CTA

Filter/mute PB-638:
All electrolytic capacitors
All 2sc1345 with BC550CTA
All Tantalums with Nichicon UKL
All VD1221 diodes

Flat Amp PB-640:
All Electrolytic capacitors
All 2sc1345 with BC550CTA
All 2sa640 with 2sa992
All Tantalums with Wima Film caps.
All Resistors in audio path (after preamp section, attenuator) with metal film.

All service I did after the noise issue was done one board at a time and then tested. Function and noise issue remaind the same after each board service and test. I even fixed and cleaned up the prior techs sloppy work. That is where I am at, still have the original noise level issue and current significant noise issue in the left channel. When working this was the most spectacular amplifier I've ever heard, and I would love to have that feeling again, any help would be greatly appreciated, thanks.
 
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By noise do you mean a constant noisy background? Do you have noise without the input signals? A little video may help to understand the noise you mentioned.
 
Constant noisy background. Noise remains consistent without input signals. Sounds like ground hum if I had to describe it.
 
sanjib said:
Are the main filter capacitors replaced?
Click to expand...
They are original. The reason I eliminated them as an issue was that, I can swap the left and right main filter capacitors by swaping each power amp section's connectors and the noise does not follow an individual filter cap. Am I wrong in this assessment?
 
You have noise only in the left channel and no noise in the right channel. When you swap the amp card the noise swap to the right channel. Is that what you saying?
 
sanjib said:
You have noise only in the left channel and no noise in the right channel. When you swap the amp card the noise swap to the right channel. Is that what you saying?
Click to expand...
The only thing/swap that changes the noise ( from the left to the right) is when I swap the signal input connectors going into the power amp sections.
 
If swapping the amp card does not swap the noise in channels then how do you eliminate the main filter capacitors from the problem list? When you are checking the amp section only you are connecting the signal directly in the main-in amp ports?
 
sanjib said:
If swapping the amp card does not swap the noise in channels then how do you eliminate the main filter capacitors from the problem list? When you are checking the amp section only you are connecting the signal directly in the main-in amp ports?
Click to expand...
At the bottom of each power amp section there is the signal in connector essentially from the preamp section. At the top of each power amp section there is a connector with the audio output going to the relay prior to speaker output, and that connector also supplies the main power and filter caps. during troubleshooting I swapped the top connector on the power amp sections, thus swapping the main filter caps too and the noise did not follow the swap ( not unique to one filter cap). Hope this description helps.
 
If swapping the amp card does not swap the noise, I think amp boards are fine it is coming after the main amp. Usual suspects are speaker selector switch and relay. From the schematic, it looks like there 2 relays. Am I right? Can you post some pics of the boards?
 
sanjib said:
If swapping the amp card does not swap the noise, I think amp boards are fine it is coming after the main amp. Usual suspects are speaker selector switch and relay. From the schematic, it looks like there 2 relays. Am I right? Can you post some pics of the boards?
Click to expand...
After the power amp boards there is one relay located on the Power Suppy board PB-647. (This relay was replaced by previous tech). After that the signal goes to the speaker select switch. I have removed the audio path/wires from the speaker select switch and the noise is the same upto that section. This is one of the reasons the more I troubleshoot the less it seems to make sense to me, it all seems counterintuitive. I also don't think it is the relay because I can get the noise to switch channels at the speaker select switch stage by swapping both the power amp section's signal input wires.
 
The schematic I am looking at shows one relay (probably s signal relay) between the main-in port and the input stage of the main amp. It is located in the board where all the components are numbered 300s but there is no board number.
 
sanjib said:
The schematic I am looking at shows one relay (probably s signal relay) between the main-in port and the input stage of the main amp. It is located in the board where all the components are numbered 300s but there is no board number.
Click to expand...
Yes, that is correct. The L-100 manual has some missing documentation. Particularly the board you are speaking of, the Touch mute/Filter (PB-638). In the sevice manual it has no documentation beyond the location diagram and the schematic, where is is unlabeled and shown in the center area.
It does have the relay you mention, a 12v relay. Part of the Touch Mute. It was one of my areas of interest too. I cleaned the contacts and have proper continuity going through it. The relay at rest allows full pass through of the audio signal, only when the Touch mute is activated does the relay activate to pass the audio signal through a -20db attenuation.
 
I would suggest disconnecting C09 and C10 on the amp board. I think C09 is a ground pin, check it (if yes make it connected to the chassis). Then feed a signal directly at C10 and check the noise in the problem channel.
 
sanjib said:
I would suggest disconnecting C09 and C10 on the amp board. I think C09 is a ground pin, check it (if yes make it connected to the chassis). Then feed a signal directly at C10 and check the noise in the problem channel.
Click to expand...
Yes C09 is the ground pin. After disconnecting C09 and C10, I connected C09 directly to ground as recommended and the noise was still present after the power amp board.
 
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