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Luxman L-100 faulty channel

quadmatrix82

quadmatrix82

AK Subscriber
Subscriber
hi all, I purchased a non working Luxman l-100 in pretty good condition, I’ve started to refurb it but hoping to get some help where to look next to solve the faulty right channel so far can confirm

- both amp modules are working well when used directly as a power smp
- bias and offset holds ok
- power supply voltages at c07-10 look good approx 57v
- right channel when used as a integrated is low and distorted

- Both channels have hum regardless of volume level and regardless if pre-main in out links are connected - the hum doesn’t get louder or softer with volume adjustment.

So far I have recapped the unit, replaced the vd1221 diodes with pairs of 1n4148, replaced zeners and replaced all the 2sc1345 with bc550c

Relay clicks out of protection

I see no broken grounds or cables or bad joints any pointers where I can look next?? Thankyou
 
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These are picky units.

I wouldn’t use a BC part for a 2SC, best is KSC1845.

How are the other two relays? The one on the phono board (I’ve had to replace that big cap soldered on to the connector just to get it to go) and the relay on the preamp board?

Tighten all your grounds.
 
I assume you have tested the preamp output with another amp or headphones? All your voltages? Rebuild the eq board inside the perforated cage there are some known problem transistors there and recap. All switches, controls and pots cleaned? I have one with a distorted right channel but it’s the amp module with crossover notch distortion and a wandering bias as the preamp output is clean. Pay attention to the relays including the one for the touch mute. I have probably done 10 of these. Replace the tantalum’s and check, resolder all the wiring as some are known to separate from the pins1728227955684.png
 
ivandezande said:
These are picky units.

I wouldn’t use a BC part for a 2SC, best is KSC1845.

How are the other two relays? The one on the phono board (I’ve had to replace that big cap soldered on to the connector just to get it to go) and the relay on the preamp board?

Tighten all your grounds.
Click to expand...
Thankyou:) I suspect relays now too do you know where they can be found? I’ll check the grounds! Big cap on the connector is replaced
 
jefferylhenr said:
I assume you have tested the preamp output with another amp or headphones? All your voltages? Rebuild the eq board inside the perforated cage there are some known problem transistors there and recap. All switches, controls and pots cleaned? I have one with a distorted right channel but it’s the amp module with crossover notch distortion and a wandering bias as the preamp output is clean. Pay attention to the relays including the one for the touch mute. I have probably done 10 of these. Replace the tantalum’s and check, resolder all the wiring as some are known to separate from the pinsView attachment 3313399
Click to expand...
Thanks for these tips! I have recapped and replaced the 2sc1345 and zeners on this board, all pots and controls cleaned…connections look good, I’ll buy the relays just need to find them any suggestions where to look? I’ll try test it as a pre to confirm findings and report back, I haven’t measured any voltages for the pre if you have any suggestions which spots to check I can do it and report back?
 
There are two trimmers on the power board. If you look at the schematic, you will see that they are connected to a - and + voltage transistor (left and right). I can’t remember which leg. Measure and adjust that +/- voltages to ground.
 
jefferylhenr said:
There are two trimmers on the power board. If you look at the schematic, you will see that they are connected to a - and + voltage transistor (left and right). I can’t remember which leg. Measure and adjust that +/- voltages to ground.
Click to expand...
Thanks I should have been more specific these are adjusted +/- 58v

I had a look at the relays visually the touch mute one does look a little oxidised the other looks ok I’ll order both fit and see how this goes.
 
jefferylhenr said:
I assume you have tested the preamp output with another amp or headphones? All your voltages? Rebuild the eq board inside the perforated cage there are some known problem transistors there and recap. All switches, controls and pots cleaned? I have one with a distorted right channel but it’s the amp module with crossover notch distortion and a wandering bias as the preamp output is clean. Pay attention to the relays including the one for the touch mute. I have probably done 10 of these. Replace the tantalum’s and check, resolder all the wiring as some are known to separate from the pinsView attachment 3313399
Click to expand...
relays on order if you have any voltage check suggestions happy to test and report back I’ll look over grounds and wiring also in the interim
 
While you're waiting, I would recommend going over all of your solder connections and component orientation. Check the wire wraps on the pins on the boards. I had a few break off simply by moving the boards to change components. Also, I remember the selector switch being extremely dirty causing dropouts until being cleaned. Before and after pictures.

20221230_145652.jpg20221230_145722.jpg
 
Bruno Primas said:
While you're waiting, I would recommend going over all of your solder connections and component orientation. Check the wire wraps on the pins on the boards. I had a few break off simply by moving the boards to change components. Also, I remember the selector switch being extremely dirty causing dropouts until being cleaned. Before and after pictures.

View attachment 3313975View attachment 3313976
Click to expand...
Cheers I actually just rewired these for longer length to make it easier to work on the boards I haven’t cleaned the pots before that way I might try it
 
So I have some good news to share!

Replacing the 24v relay in the eq/phono board pb-636 solved the distortion issue

I’m still waiting on the 12v touch mute relay to arrive I’ll replace it anyway when it arrives.

Not so good news - I still have hum on both channels…

Both channels have hum regardless of volume level and regardless if pre-main in out links are connected - the hum doesn’t get louder or softer with volume adjustment, I don’t see any broken wires and made sure the black ground cables were secured. Any suggestions how I can track this down? I wonder if it’s normal given the chassis is all open without face plate and sleeve etc???
 
Possibly a failed or tired voltage regulator. It may have failed short or could also be a bad cap(replaced) or maybe zener(replaced). Look for a regulator that supplies the front half of the power amp stage, look for elevated voltage and ripple. In the absence of an oscilloscope to could try detecting increased ripple by measuring Vac.

edit
Check AC then DC voltage at C07S(or C12M) and C10S(or C11M). With AC measure then remeasure reversing probe orientation.
Cheap MM will respond differently.

Q901 is the main regulator on the +ve rail, controlled by Q903,5,,,,
Q902 is for the -ve rail. Problem could be with either. Looking for some significant difference in voltage measurements between those rails.
 
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mbz said:
Possibly a failed or tired voltage regulator. It may have failed short or could also be a bad cap(replaced) or maybe zener(replaced). Look for a regulator that supplies the front half of the power amp stage, look for elevated voltage and ripple. In the absence of an oscilloscope to could try detecting increased ripple by measuring Vac.

edit
Check AC then DC voltage at C07S(or C12M) and C10S(or C11M). With AC measure then remeasure reversing probe orientation.
Cheap MM will respond differently.

Q901 is the main regulator on the +ve rail, controlled by Q903,5,,,,
Q902 is for the -ve rail. Problem could be with either. Looking for some significant difference in voltage measurements between those rails.
Click to expand...
Dc voltage measurements approx +\- 55v with 100dim bulb on c07 and c10

Removed the power supply board and fitted new relay and q901-2, 3,5. I noticed one of the 2sc945 didn’t test too well and r933 560 ohm was dark so changed it even though tested well

measurements were same before and after, zeners and caps are new on the board but the hum remains
 
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Update - the volume hum changes with the attenuator pot being adjusted strangely it’s hum volume is the loudest at the centre of the pot and is almost least loud at min attenuation and not so bad at max attenuation middle of the pot is the loudest - no difference with the volume pot or balance pot attenuator only.
 
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