Beomaster 8000: Continuing the Board Recap

Three more circuit boards are now recapped...old electrolytic and tantalum capacitors replaced with new 105°C electrolytic capacitors or polyester (WIMA) capacitors where applicable.

Here is the Beomaster 8000 preamplifier board (from various angles) before recapping.

Here is the board after the recap.

Along with the capacitor replacement I also reflow the solder joints on all of the board connectors and on this board I cleaned the input trimmer contacts with contact cleaner. The solder joints on those trimmers were also reflowed.

Next to the preamplifier board are the FM and FM Interface boards so they were next to be recapped.
Here is the before picture.

Here are the after pictures.

The last board in this set of board recapping is the Tone Control and Filter board.
This is the before recapping picture.

This is probably the simplest board to recap in the Beomaster. Here is the after picture.

That leaves just the display and microcomputer boards to do before this Beomaster will be ready for a test drive.

Beomaster 8000: FM & FM Interface Board Rework

The FM & FM Interface board assembly (the two boards connect together) appear to have been at the heart of the post burn-in failure that threw a circuit breaker in AC line powering the Beomaster. Once I had rechecked the power supply and output amplifier boards, I found that the Beomaster power up relays for the ±55 VDC rail voltages would fail to engage due to the Beomaster's fault protection circuitry. Unplugging power from the FM Interface board fixed the problem and I began using a spare FM/FM Interface set of boards for the Beomaster tuner.

My plan was to find the bad parts in the FM boards during the recap process and then re-install them. I discovered several defective transistors and a defective diode. This picture shows a couple of the damaged components on the FM Interface board. Since those components were bad I also replaced the three OpAmps on the FM Interface board.

After repairs were made to this board I re-installed it back into the Beomaster. Upon applying power and first selecting TP1 as the source input, I immediately started hearing a buzz in the speakers. Power was quickly removed as well as the FM board assembly. Something there is still not right. I am lucky nothing got damaged and installing it was not my best idea. This board needs to be wrung out on the bench by itself before testing it again in a Beomaster. 

To move forward with this project I decided to take one of my spare FM assemblies and use it. I selected the FM assembly that was closest in part number to the removed FM assembly.

Like the removed, faulty FM assembly I had replaced the electrolytic and tantalum capacitors plus the three TL072 OpAmps. One difference with this spare is that I used sockets for the OpAmps so I could experiment with different OpAmp types. The installed OpAmps here are OPA2134PA chips. The same kind I used in the Filter & Tone Control board.

To be consistent and to provide peace of mind, I decided to replace the TL072 OpAmps in the preamplifier board I completed earlier. Here is the preamplifier board with the OPA2134PA OpAmps installed.

This completes all but the Beomaster Display and Microcomputer boards. I will tackle the Display board next as it requires the most work in updating the displays modules with SMD LEDs.