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Monday, January 15, 2018

Beomaster 8000: Removing the Output Amplifier Boards and Power Supply for Recapping

It has been quite a bit colder in the workshop the last week. Another cold front is arriving tonight but work must continue on the Beomaster 8000. I had to plug in an additional heater in the workshop to keep things toasty.

The next step in the restoration is to replace the electrolytic and tantalum capacitors on the two output amplifier boards and the power supply board. The reason I am doing those as a group is because of their physical location in the Beomaster.

The output amplifier board is identical for the left and right channels. The only difference is the color coding on the wires that connect to the speaker switches and the headphone jack.

I prefer to do the recap restoration work with the boards removed. In the case of these output amplifier boards they can also be tested outside the Beomaster by applying the necessary ±55V and +15V supply voltages.

Removal of the output amplifier boards requires removing the output transistors from the big heat sinks. It would have been nice if the output amplifier board had enough room to slide out the back of the cabinet without removing the heatsink mounted components. There are just too many wires in way.

It is worse on the left channel and the cabinet ledge for the lid damper (damper is removed in the photo) blocks any chance of the board sliding out.

So heat sink component removal it is.

The thermal paste for the transistors has usually started to dry out by now so I don't mind the exercise as it should ensure long term protection for the parts.

Here are the left and right output amplifier boards removed and ready for recapping.

This is also a good time to pull out the power supply board and its heat sink with the voltage regulators.

While these boards are out I will clean out any dust and debris from the cabinet where those components live. I like the feeling of knowing the Beomaster is clean like new again after the restoration.

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