Technics SU-VX500 Amplifier Internal & Cleaning Process

I have been working at home since last Thursday, this is because of the corona virus pandemic that spread already. Stay safe everyone, stay at home.

Actually it is quite boring if not do something related to my hobby. So in this opportunity I pull out my old Technics amplifier from the cave. This amplifier is built around 1991, the model is SU-VX500. It is still made in Japan and the great things about this amplifier is the Class-AA patent technology that quite make this amplifier famous at that time.

So let see the inside and I will do a lot of cleaning to make this amplifier like new again.

This amplifier is full of dust. No wonder for the amplifier living more than three decades that only sit on the storage room.

The good things is all condition is almost perfect. No sign of missing knobs or broken parts.

Opening the top cover you will see this amplifier is using Technics own proprietary power IC. Not like others brand that mostly using the old Sanyo STK IC amplifier, this IC is made by Technics to simplify the discrete power transistor.

This power IC is link to the Class AA module board that vertically mounted. It consist of several transistors before going to the IC.

This amplifier has two big power reserved capacitor covered with plastic case that become this amplifier main attention.

The plastic covered is hide the capacitors brand inside.

Moving to the right panel, there is a phono pre-amplifier module using an op-amp and several transistors.

As I said earlier, this Class-AA amplifier is simply because of the line input of the amplifier IC is pre-biased by using transistor configuration that running on Class A. It is not the power IC amplifier that biased on Class A configuration.

This configuration made by Technics engineering to feed the power amplifier IC signal input with constant voltage act like in the Class A mode although the power amplifier itself is running on Class AB. This method gives the amplifier as efficient as the Class AB amplifier but sound like the Class A biased amplifier.

Finished with the internal components, I am going to the next steps is clean up all the knobs and the front panel.

Once the knob are completely clean, I can see the color is not black. It is dark purple aluminum.

Pretty cool!

I clean the dust on the panel using a cloth. This is to remove thick dust before going to the deep cleaning with brush.

I need open up the board inside the front panel, so all nut and bolt should be remove first.

This is the volume control module which using mediocre pot.

All module has their own socket so the removing process is quite easy.

I also removing the back panel for easy access on the components inside.

Phono pre-amplifier is removed for further cleaning process.

The big capacitors is also removed.

I disconnect the power cable by lifting the socket locking mechanism. This amplifier is easy to work on since all components inside are basically removable.

With the back panel open and the transformer cable removed, now they can separate from the amplifier chassis.

The front panel is also removed so only the main board and the chassis remains right now.

All dust is clean up including the capacitors base plate is cleaned as well.

First attempt for cleaning is by using cloth and swipe the board surface.

This is the power IC photo in close up.

I wish to open the bolts on the IC to separate from the heat sink. But I stop to do that since I think it is not necessary.

I adding new small bolt for securing the amplifier feet. The original feet attach to the chassis is only using the plastic molded to hold on the chassis which not strong enough. So adding a bolt for securing all four feet is a great option for the holding the feet's attach to this heavy amplifier unit.

With brush and cleaning solvent, now the chassis is clean as new.

I continue cleaning in detail of every parts in the main board.

Now it is clean like new.

I continue to cleaning up the power transformer.

Then I clean up the back panel as well.

Then I continue open up the front panel board.

Jump to the phono pre-amplifier board, I noticing the transistors using in the circuit is 2SK170 for the input stages. Very surprising since this FET transistor is well known for good sounding audio transistor.

I clean up the front panel and it is look like a new unit.

The final step is assembly all components again.

I am using the cable ties to tidy up the cables.

Installing the front potentiometer screw.

All bolts and nuts are in place but what is this steel bracket came from?

I forget where it should put on.

After takes some times to figure out, finally I know there is the spot where it should be put on.

The remaining process is put all knobs on.

I check the amplifier DC offset based on the service manual and the result is as specification, within the measurement range.

It is all done.

I using the direct mode for better audio performance as said on the manual and his amplifier sound very good. It is dynamic, detail with warm vocal.

But this amplifier not operate perfectly. The switches inside not perfectly contact. I found that several things need to be replace is the speakers switch relay, switch for selector and potentiometer that already degraded by time.

But for now, I am quite happy to have this amplifier in this clean condition.

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