Luxman M-300 Repair And Restoration

This Luxman M-300 power amplifier is in good cosmetic shape but is in need of some repair and restoration.

You can run this Luxman M-300 power amplifier in class AB or class A with a turn of a switch.

This Luxman M-300 power amplifier came with a nice wood case.

There are several screws that hold the wood case to the chassis. Once removed the chassis will pull out from the front.

The first thing that I notice with the chassis out of the case is that the positive speaker terminal for the left channel is broken off.

There is plenty of wire so I should be able to replace the speaker terminal without to much trouble.

The replacement speaker terminal is not an exact replacement but it's better then none at all. You can only tell the difference at the back of the M-300.

With this Luxman M-300 power amplifier out of it's wood case I can get a good look at it's layout.

This Luxman M-300 has a very large heatsink area. Any amplifiers that run in class A usually do.

There is some dirt and dust that needs to be cleaned up. Almost all vintage audio repair or restorations involve plenty of cleaning.

With the bottom cover removed on this Luxman M-300 you can see the output transistors and driver boards.

I am able to clean the pots and switches with dexoit without removing the faceplate. I use a piece of paper towel in the chassis to catch any overspray or dripping.

A small portable LED light can help you to see in those dark areas.

I will be reseating the power transistors with new insulators and new thermal paste. After 40 years of service it's time.

The three power transistor heatsink assemblies will need to be removed from this Luxman M-300 power amplifier.

I have removed the first heatsink assembly. You can now see the four power transistors that are associated with the first heatsink.

The old dried up thermal compound will be cleaned up and fresh thermal compound will be applied.

Cleaning up the old thermal compound and adding new will allow the power transistors to dissipate heat more efficiently.

I have cleaned up the first heatsink during this Luxman M-300 repair and restoration. Two more to go.

With all three heatsink assemblies removed I can now clean the old thermal compound from the twelve power transistors.

I have cleaned up the old thermal compound from the power transistors during this Luxman M-300 repair and restoration.

With the heatsinks removed I will be able to replace 40 year old electrolytic capacitors on the protection, class A/AB, relay board.

I have replaced the original electrolytic capacitors with high temperature rated Nichicon capacitors that should last for many years.

Most of the assemblies in the Luxman M-300 power amplifier have enough slack in the cables to make component replacement easier.

The Driver/Regulator assemblies have several electrolytic capacitors that will be replaced during this Luxman M-300 repair and restoration.

Once again there is enough slack in the cables to get the Driver/Regulator assemblies in a position to access the components.

There are several "audio grade" capacitors in the Luxman M-300. I will be using Nichicon Muse capacitors where audio grade capacitors are needed.

Sometimes you need to put the chassis in different position to get better access. Also, I have put a piece of bubble wrap on the face to protect it.

I have replaced the 40 year old electrolytic capacitors in one of the Driver/Regulator assemblies and I'll reinstall it.

I have now completed the electrolytic capacitor replacements on the second Driver/Regulator assembly and I'll reinstall it.

I have installed new power transistor insulators along with new thermal compound. I'll reinstall the heatsinks next.

With all of the assemblies reinstalled this Luxman M-300 power amplifier repair and restoration is getting closer to completion.

I now have a CD player plugged directly into this Luxman M-300. I'll give a listen on the test bench and see if everything sounds okay.

Both class AB and class A sound fine. 40 watts per channel in class A mode, 150 watts per channel in class AB mode.

In class A mode this Luxman M-300 run's very very warm(hot). Never block the top ventilation opening at the top of the power amplifier.

You must follow the service manual for the Luxman M-300 to set the idle current for both the class A and class AB modes.

There are two pots that you adjust for the two different idle currents on the Luxman M-300.

Any vintage audio repair or restoration should include bench testing with test equipment that is made to measure power, distortion, etc.

Both channels tracked very close to each other. This will allow both the left and right channels to sound balanced when listening to music.

The distortion numbers were very good on both channels throughout the various frequencies that were tested.

This Luxman M-300 power amplifier tested well on the test bench. It's about time to put the wood case on and listen to some music.

This Luxman M-300 power amplifier repair and restoration in complete. It's time for some music!

 

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