Resurrection of the Luxman L550

RuffzGuts

RuffzGuts

Super Member
Hello again all,
Well I have finally, after completing many other projects that were in the way managed to get back to working on my Luxman L550.
When I originally obtained this amp, unfortunately the previous owner had already been in and made attempts at repairing it, so as well as the wear and tear that the operating temp does to the boards and components, the delicate pcb’s were not in good shape particularly around the main amplifier…it also had some melted wiring and many cooked capacitors…

So anyway, at this stage, all I want to do is replace what I need to in order to hopefully get it operational before going any further…
Working on this amplifier has been painfully time consuming so far, but I am sure it will be worth it in the end!

There seems to be limited supply of detailed pictures of the internals etc of the 550 so will try and document the amp as best as possible as I work through it and share Pictures here…bare in mind this may take some time as this is very much a long term project.

Ok first advice I would like to ask is regarding re applying thermal compound to both heat sink and power transistors and silicon pads…
Suggestions on what type of compound to use, and how to go about it without making a mess….
It’s going to be a fiddly job, I am in the process at the moment of replacing wiring on the main amp boards, and I can tell you, just getting these pieces back together even without thermal compound is going to be a small challenge….
As always, much appreciate any help or advice…Cheers Ruff.
 
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First Pics
 

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more pics

pics 2
 

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"re applying thermal compound to both heat sink and power transistors and silicon pads…"

Silicon pads are one use only, and don't require thermal compound, did you mean mica?
50 watts of pure class A sure cooks the hell out of everything, I guarantee the main filter caps are done. my L-530 ( 15 watts class A 120 watts A/B ) sucked the life out of the main filter caps.
BTW the L-510 / L-530 / L-550 were only sold in Japan, europe and Canada
 
ryuuoh said:
Those are some impressively over heated caps!
For heatsink compound, I use the bog-standard white ceramic stuff. Not making a mess is a technique to learn by experience, but I try to apply as thin a coat as possible on the mica insulator. You could try the newer thermal pads and eliminate the grease altogether.

http://www.digikey.com/product-sear...=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25

This might be of some interest:
http://amp8.com/tr-amp/lux/l-550x.htm
Click to expand...

thanks for that link, although a different model to my amp, certainly well documented, it does show just how much work goes into restoring these Luxmans...a class jobs been done on that one.
 
Denten said:
"re applying thermal compound to both heat sink and power transistors and silicon pads…"

Silicon pads are one use only, and don't require thermal compound, did you mean mica?
50 watts of pure class A sure cooks the hell out of everything, I guarantee the main filter caps are done. my L-530 ( 15 watts class A 120 watts A/B ) sucked the life out of the main filter caps.
BTW the L-510 / L-530 / L-550 were only sold in Japan, europe and Canada
Click to expand...

Yes my mistake, Mika pads....MT200, I do hope the main filter caps are not done as they are 30,000uF and i have searched for replacements before with no luck...although I am sure there are other options or mods that can be done...

I didn't know they were only sold in Japan Europe and Canada...But i was told by the wife of the previous owner that her husband had brought the amp back him self from Japan...
 
Thing is, i was just going to have a crack at it...but I thought it might be better to use different compound for the plates to heatsink tube connection, which was pretty heavily caked on....( i know more isn't better) i have compound here which is kind of like a tooth paste kind of texture that i think will be good for that....but as far as the output transistor connection..and mika insulators ....well should i be using a CPU type of compound? also the mika insulators had grease on both sides...

I guess this is just going to be a trial and error kind of thing...just thought ide ask how you guys go about resetting mt200 transistors...
 
correct Luxmans do not run hot, the excess heat doesn't get out, it is burning internal components.

the computer compound could be conductive, do not use one that is.

all the compound is for is to fill all the uneveness between the parts to better transfer heat. Metal to mica to metal is best but these do not mate 100% so the paste fills in the microscopic nooks and crannies. Use as little as you can to cover the pieces.
 
Ok, had a Bugger moment today...snapped off a STV-2H varistor...live and learn!...dont try and manipulate these things ....I think i have found a source for this part...Hopefully after reading a few threads on here...

The heat sink compound i have on hand...some cheap ebay stuff i purchased a while back is IDL-280 not sure on its conductivity, i think i will definitely be using it on the plate to heat sink tube connection...unless someone screams NO!...but would appreciate a better suggestion for the output transistors, or should i just use the IDL-280 also?
 
Blue Shadow said:
correct Luxmans do not run hot, the excess heat doesn't get out, it is burning internal components.

the computer compound could be conductive, do not use one that is.

all the compound is for is to fill all the uneveness between the parts to better transfer heat. Metal to mica to metal is best but these do not mate 100% so the paste fills in the microscopic nooks and crannies. Use as little as you can to cover the pieces.
Click to expand...

The L-550 is 50 watts class A, so yes it does run hot :yes:
 
You're screwed for wrecking that STV-2H. Those are impossible to come by, and I would not trust a homebrew replacement in this amp. It's super critical that it works exactly right, or you'll practically have a fire to deal with (aside from a truly irrepairably broken amp).

You'll need to get another amp that uses it (many do) and harvest it for parts.

You must replace the main filter caps. They've been seeing ultra high ripple current all their life. This kills capacitors. Normally these will be fine in an old amp, but not when it's class A only.

30,000 µF is a nonstandard value so you won't find that. 33,000, 22,000 or even 10,000 will do just fine for a replacement. Mind the dimensions, I believe Luxman used some custom made caps here, with fairly low height. New 33,000 caps may not fit.

For thermal compound, definitely use the cheapest stuff there is. Difference will be minimal, especially in this application. On mirror finish computer parts, there can be differences between greases, but these old heatsinks and transistor surfaces were cut with broken hacksaws so it won't matter what you use.
 
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ZOOM said:
You're screwed for wrecking that STV-2H.

:pity: don't say that!! Yes well in searching for the part all the threads start appearing ...bangs head...I may need to attempt a repair on the broken one...

As for filter caps, yes they are short, I have found some nice Vishay 33000uF 100v I would like to use, but they are like most caps in this range 105mm tall, I need 63mm diameter by 85mm tall...

I through my Peak esr meter on them this morning, both are low in capacitance ,around 24000uF esr looks ok...but i think youre right in what you are saying..they are under constant load...I would like to replace them...they also need to be under 64mm diameter as they protrude through a metal cover that clips over the top of them which also holds some boards in place...
Click to expand...
 
STV-2H Repair

Well I had a crack at it and won!...I feel confident in the strength of the joint :thmbsp:

How i done it,
Dremel with and engraving attachment, carefully excavated around broken wires, this was actually pretty easy and i could get right in and around the wires without it tearing the thing to pieces.

i then took some very fine sand paper and polished the broken wires as best i could to allow the solder to take.....

I then dropped a dob of solder on both pins...

then i took some fine wire, about 5 strands, folded and twisted to get a loop at the joint end

I then tinned the loop with solder, sat the now soldered loop on top of pin, then just gave it a quick touch with the iron and bobs you uncle...:yes:

I guess i should epoxy over it, but to be honest it does actually feel really strong as it is...
 

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stv-2h

:D ready to go back on....I now know to try and avoid ever touching one of these things again
 

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Does anyone Know anything about the Nippon NXA series capacitor? the green toasted ones pictured earlier...I cant seem to find a data sheet on them....
 
Ok, been doing a bit more on the amp, just something that anyone might want to take a look at if they have this model, like many amps, the glue used to mount the capacitors is nasty stuff...it corrodes anything metal near it...I seem to have lost some earlier photos but on boards PB-1400-2 there are two of these...i did need to replace the IC (IC352) the legs on both of them were pretty well much corroded right off due to being mounted so close to a c358 capacitor and the glue residue...its really nasty stuff...if you have this amp in original condition this is something that needs to be addressed immediately.

This is also a problem on board PB-1401-1, IC402 is again located right next to glue, this may vary where the glue has been placed, I might be lucky to save this IC, i will remove it and try and clean the legs up as best as possible
 

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