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Luxman L-480 Overheating Help

David Weaver

David Weaver

AK Subscriber
Subscriber
Luxman Rig.jpg

I have this beautiful Luxman rig that I acquired from my brother but the amp (L-480) has an issue that is apparently common to these models. I did find the following that best describes the problem from Geoffrey Kolbe (May 6, 2008) on an other forum:

"There seems to be a problem with a particular transistor pair (2SA 949 and 2SC2229) in the power amplifier section which can lead to an intermittent fault. The transistors run very hot and as they age, one of them can break down intermittently, (probably Zener breakdown as the rail voltage is quite high at 53volts), changing the quiescent DC output voltage of the amplifier. The DC voltage should be zero, and a relay disconnects the speakers if the voltage rises to +/- 1 volt or so. The red light on the front panel starts to flash, (as it does at switch on as the voltages settle) Replacing the 2SA 949 and 2SC2229 transistors with a pair of transistors that can take a heat sink would be a good idea."

Would anyone one on AK experienced the same issue and if so, what did they do to remedy it or who could I contact to get the unit repaired?

Thanks!
 
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I thought I would resurrect this thread.
After recently being told my L-480 was not repairable, I decided to take a shot at fixing it.
I read the post: "New Acquired Luxman L480 Surprise!" that detailed the similar issue I was having with mine. (The pre-drivers going Chernobyl)
I plugged her into my dim bulb and flipped the switch, only to find the bulb glowing solid. Upon further investigation of the drivers I saw they were slathered with silver paste. I unbolted the drivers from the heat-sink, cleaned up most of the paste and tried the dim bulb again.
This time the bulb glowed bright and then settled to dim. I then swapped out the pre-driver for some TO-126's and she came alive.
Unfortunately, when trying to set the bias and DC offset, the VOM was jumping all over. I suspect the trimmers need replacing but when I look up 330ohm trimmers on Mouser/Digikey, there are none available.
Can I use a 500ohm in place of the 330?

Crispy.jpg DriverMess.jpg NewPreDrivers.jpg Trimmers.png WorkingNow.jpg
 
Yes. All you need it settings about where the VR is now. I usually go up to the first one available.
 
Shoot those new transistors to see what temp they go to. Are these mounted to the underside of the board when the amp is in place? I'd put heat sinks on those transistors. Luxman didn't use those heat transfer engineers much back in the day and I have seen a few charred pieces.
 
Thanks Blue Shadow! I checked the temp with my DMM and the hottest trans was 55 Celsius.
I made some heat sinks from some copper I had that I'll mount tonight with some proper thermal grease.

DIY_HS.jpg
 
Those look like they will help get the heat away from the components. Copper, better than the Al sheet heat sinks available from D & M.
 
I installed my "MacGyver'd" heatsinks and then took another crack at bias and DC offset.
The unit was much more stable (heatsinks???) and I was able to adjust the bias to 26.4mv and the DC offset to under 20mv.
Trans temps are still around 50C so I may add a small 5v fan to help keep them cooler.
I plan to replace the trimmers and replace some of the caps as well.
I'm really pleased she actually works and sounds amazing to boot!

DIY_HS_Installed.jpg
 
Would it better to install the heatsinks on Q408ab with the long side up like Q407ab? The heat will dissipate upward away from the transistor and there will be less chance of shorting the legs.
 
vinnysj said:
Would it better to install the heatsinks on Q408ab with the long side up like Q407ab? The heat will dissipate upward away from the transistor and there will be less chance of shorting the legs.
Click to expand...
Thanks vinnysj, I looked at them again and they are all mounted with the "long side" up. The previous pic is kinda of an optical illusion.
Here is a different angle.

IMG_4676.jpg
 
David Weaver said:
Thanks vinnysj, I looked at them again and they are all mounted with the "long side" up. The previous pic is kinda of an optical illusion.
Here is a different angle.

View attachment 2735097
Click to expand...
Hi, I have a hot running L-480 also. I've enjoyed reading the thread. Which transistors did you end up using and how many? I looked up on the service manual, I couldn't really see the part in the lists. TIA
 
I used a pair of KSA1220A-Y and KSC2690A-Y's. I forget which one is end of life but you can still get them from Affinity For Artifacts.

LuxmanTransistors.jpg

These are beefier than the originals but they still put out a good bit of heat. Heatsinks required!

I hope you get yours up and running. Beyond the heat issue, they are wonderful sounding units!
 
Hi. Thanks for your reply and the tip. I went down to the local computer shop and showed the young fellow the heat sink and power transistors. He is working on a solution for a better heat sink and perhaps a CPU fan. He also wants to clean the inside of the unit completely. The power transformer is also over heating. We'll see how we go. Did you remove the old heatsink and install a better one?
 
If the "old heat-sink" you are referring to is the large heat-sink cooling the main driver transistors, no I did not replace it. The L-480 and I believe the 580 as well has special fluid filled radiator heat-sink for the mains that works really well. The heat generation is greater from the pre-drivers than the mains. As for the transformer, mine does get very warm but it not too hot to touch.
 
Ah, Ok. The computer store washed their hands. We managed to find a "specialist" fingers crossed. He finished my sentence when I referred to "overheating" and said he had a good parts supplier. He has many photos of equipment like McIntosh. This is the 4th person I've taken it to. It's very difficult to find a trustworthy honest person here in Mex City. Most people seem to say the heat sink is inadequate. Anyway, let's see. I will post an update. Thanks again.
 
Honcho52 said:
He finished my sentence when I referred to "overheating"
Click to expand...
That might be good. No reason to replace the liquid cooling loop if it is undamaged. The heat in the pics above are not the power transistors which are attached to the heat pipe. Luxman has a few units that have transistors that will char the board and attaching heat sinks to these can be a big help.

Hopefully you found a good tech for your unit.

But what do you mean by overheating? These things generate heat and are designed to run warm at least.
 
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