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Tuesday, September 18, 2018

Texas Beomaster 8000: Preparing for cabinet cleaning and reservoir capacitor replacement

The Beomaster 8000 unit from Canada has its cabinet nice and clean, output amplifier assemblies re-installed, reservoir capacitors replaced and new speaker switches. Now it is time to catch up the other Beomaster 8000 unit from Texas.

I will start the Texas Beomaster 8000 out with clearing the cabinet to check for rust and prepare for the reservoir capacitor replacement.

The inside of this one needs cleaning for sure but I don't see any troublesome rust damage.

So far so good. I will remove the base plate and check under there.

Again, just some dirt but no rust. The base plate does have a number of areas where paint has scraped off so I will repaint it to insure no rust starts.

That leaves me with the Beomaster 8000 frame, the big and small transformers, speaker switches and the reservoir capacitors.

The next task will be to replace the four reservoir capacitors. After that I will change the speaker switches then reinstall the left and right output amplifier assemblies.

Monday, September 17, 2018

Canada Beomaster 8000: Reassembly of Rear Cabinet Components

The rust on this Beomaster 8000 unit is neutralized and the affected metal pieces have been repainted. This receiver is ready for the reassembly of the left and right output amplifier boards, speaker switches and the power supply board.

First though, here are some final pictures of the rust cleanup. Nothing really to say here other than to reiterate that it is better to completely remove the frame parts in order to find any rust areas hiding in the seams.

While everything is open and out of the way I like to change the speaker switches at this point. We do that just to avoid any problems with the old switches in the future. I am using a Beolover speaker switch part for the replacement on this Beomaster 8000 unit.

Here is the speaker switch wiring for the two original switches.

Here is the new switch for Speaker 1

Here are both new speaker switches installed.

Now on to the reinstallation of the left and right output amplifier assemblies I restored and tested earlier.

Starting with the left channel output amplifier assembly...

The opening has a small shelf for the lid damper molded into the cabinet frame. That makes it nearly impossible to slide the output amplifier board into the cabinet oriented the way it will be when installed.

The left channel output amplifier board must be turned 90° sideways to fit through the opening in the frame, then rotated back 90° to its installed position.

Now that the left channel board is in place I will finally solder down the left channel reservoir capacitor wires.

The right channel output amplifier assembly installation is a little easier. The cabinet frame opening for the right channel is much less obstructed.

The final steps are to mount the left and right channel output amplifier assembly heat sinks back on the cabinet frame.

The Beomaster 8000 power supply board assembly is installed and I can now move on to the next part of the restoration.

Note in the above picture that I have temporarily left the metal shield box off the remote control receiver (on the power supply board) until I test that it is working.

Wednesday, September 12, 2018

Canada Beomaster 8000: More rust to neutralize

While reviewing the last couple of blog posts on this Beomaster 8000 unit from Canada I started to question whether I was sure I got all of the rust. I neutralized the areas I saw inside the cabinet but when I turned the Beomaster over to look at the cabinet's outside bottom plate I saw the same type of suspicious corrosion on the left channel side of the Beomaster.

Maybe at some point in its life this Beomaster cabinet's left channel side was subjected to some corrosive liquid.

I removed the base plate's mounting screws and found some rust areas that were hidden by the molded frame of the Beomaster.

On the frame and rear cabinet panel you can see additional rust and some rust staining.

The frame is non-metallic so I will try some products to remove those. The rear panel is metal so it will need some rust neutralizing treatment.

Again, the right channel side is fine (other than some dust). That reinforces my theory that there was some liquid spilled on the left channel side.

I am glad I removed the bottom plate to check for more rust. This will be easy to fix and while the rust neutralizing treatment is drying I can continue restoring the other Beomaster boards.

Canada Beomaster 8000: Restoring the power supply board

The Rust-Oleum flat black paint has been applied on the left side of the cabinet as the final treatment to eliminate the rust areas I found.

While the paint is drying I performed the restoration on the Beomaster power supply board.

While I am working on this board I will change out the thermal protection on the ±15V and +5V regulators.

There is a 22uF, 25V capacitor under the metal cover for the remote control receiver circuit.

The large axial reservoir capacitors for ±15V and +5V have some rubbery glue that helps secure them in place.  I removed that glue and cleaned the board with alcohol.

...and here is the recap work and the remounted voltage regulators. I use black hot glue to secure the three large, axial reservoir capacitors. I will leave the metal cover off the remote control receiver until I can test that is works okay.

Monday, September 10, 2018

Canada Beomaster 8000: Changing the reservoir capacitors and some rust (?)

After an unscheduled little break over the Labor Day holiday it is time to get cracking on these Beomaster 8000 restorations.

This weekend I started on the Beomaster 8000 from Canada, replacing the four 10,000uF reservoir capacitors. These are the reservoirs for the left and right channel ±55V rails.

Starting with the left channel

The solder posts on the replacement capacitors are just a small post and do not provide the nice mounting terminal the original reservoir capacitors had.

To compensate I add a small, flat terminal at each end of the connecting bus-bar.

After that I added mounting terminals to the five wires that connect to the left channel reservoir capacitors. I won't connect those yet because I will need the slack in the wires when I reinstall the left channel output amplifier assembly.

On to the right channel reservoir capacitors.

There is the same issue with the new capacitors and mounting the bus-bar.

Solved the same way.

I went ahead and connected up the five supply wires with their new terminals on the right channel. They won't be in the way for the right channel output amplifier installation later.

I was actually hoping to reinstall the left and right channel output amplifiers after their respective reservoir capacitors were replaced. However, when working on the left channel reservoir capacitors I noticed something odd on the cabinet base that looked like corrosion.

So I took a little detour on my restoration step order.  I went ahead and removed all of the Beomaster 8000 boards from the cabinet so I could fully inspect the inside of the cabinet base.

The corrosion was rather strange. It is only on the left side of the cabinet (when looking at the Beomaster from the front). The areas with the corrosion remove the cabinet black paint when I wipe it with a paper towel.

There is no corrosion on the right side. Just some dust that needs cleaning up.

Back to the left side of the Beomaster cabinet I wiped all of the nooks and crannies that had the rust.

On this type of problem I apply three coats of a rust neutralizer. It will turn the rust black. After twenty-four hours I will check the result and see if any rust has reformed. If it does then I will retreat the areas again. Once the treatment is satisfactory I will be able to paint the inside of the cabinet with black, rust protective paint.

This detour doesn't really hold up progress on this Beomaster project. I can proceed to work on the Beomaster 8000 boards I removed.  I will return to the cabinet in twenty-four hours though to see if it is satisfactory to paint.