Luxman M-02 Power Amp BBQ

madtech

Well-Known Member
This one has been under my bench for years and I've finally found the time to have a look. Seems like the previous owner blew the 1302/3281outputs on the right side and attempted to replace them with some "high quality" replacements. Previous stage was also BBQ'd. When they installed the replacements they didn't bother cleaning up all the carbon. Luckily it wouldn't come out of protection with all the NTE junk in there and nothing else fried. Bought some OnSemi replacements for the outputs. Capacitor C110 is listed as 1000pf but has no listed voltage in the shop manual. It's hooked up between the base and collector so I'm thinking 100V should do it?
Copper side is a bit of a mess but repairable. Heat sink for the outputs looks like something from Star Wars.
Looking forward to getting this running again after the abuse it's been put through. I've re-capped the C-02 pre-amp and it's ready to go.















https://flic.kr/p/2cpz6Kohttps://www.flickr.com/photos/144056422@N07/
 
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Well if the C-02 is ready to go the M-02 should be next. Good Luck. I'll check back to have a look at the pics when they show up.
 
If you look close, you can see where they soldered two resistors in series to come up with the desired value....... :)
 
When I was repairing crisp circuit boards in the MB3045 amp, I was told that the char can be somewhat conductive. I removed it completely and rebuilt the board with epoxy and some board shavings for color. Works a treat and the amps sound wonderful. I don't think Luxman had heat transfer engineers, just co-op students doing that part of their design. But boy their units sound nice.

Heat pipes became common in the early 80s. must be horizontal so the liquid flows to the heat source, evaporates and flows to the sink area to condense. A lot less metal needed for these than the regular finned sinks we see all the time. They must work just fine, lots of companies used them.
 
I miss my C-02/M-02 combo every day, one of those things I should have never let go.

Good luck with your repairs, hope it all works out for you.
 
Solder re-flow is all done. Schematic shows in red what was blown. I'm debating pulling all the remaining transistors or taking my chances with my dim bulb tester......Nothing to the left of the red line has been tested.


 
Just noticed the output emitter resistors (.22 ohm\ 5W) are from 4 different manufacturers. At least they were the same color. Yet another Mouser order......
 
The new outputs are installed. Dim bulb test went fine so it looks like there are no shorts. Flipped to main power and it won't come out of protection......bummer. The red LED D102b on the right channel won't light up, so it looks like I have an issue earlier in the stage. At least there is no smoke!
 
I've got a M-02 that's toasted in the exact same place - completely roasted through the board though.

There are a lot of fusible resistors that can fail, so check those if you haven't already. Nice work so far.
 
R124b and R127b are both open. Good news is Q114 and Q115b test good. Yet another Mouser order!
 
I had a lot of them on service, very susceptible to damage and unreliable layout, even now have one, with completly burned voltage amplifier and both of current amplifiers
 
Replaced the two open resistors. Dim bulb tester showed a short this time. Took a guess on Q111b (2SA1145) and found it shorted across all three pins. Replaced Q111b and we have lift off! Amp comes out of protection, DC Offset is 0mv both sides but I can't get the DC bias down to 4.5 mv on the left channel. Best I can do is 7mv. Anything to worry about? Both channels seem to be running at the same temp. Test with speakers is next!
 
After all the smoke and blown components, at times I didn't this one would come back life. Just proves that if you take your time, anything can be repaired. The side with the slightly higher DC bias voltage (7mv) only runs marginally warmer than the other side at 4.5 mv. 2 hours in and it's still running.

 
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