Before testing the Beomaster 1900, I needed to reinstall its four output transistors, which are located on the rear heatsinks. I had previously removed the heatsinks and their old thermal paste. For this reassembly, I prefer using modern SIL-Pad thermal insulators. They are much cleaner to work with than thermal paste and provide excellent thermal transfer.

Here are the components prepped for reassembly.

Bang & Olufsen designed a clever mounting system for these transistors. Curved, metal spring clips secure the transistors to the heatsinks, effectively sandwiching the thermal insulator between them.

The output transistors are shown reinstalled below.

With everything back in place, it was time to begin testing the Beomaster 1900.

As soon as I connected the variac and dim bulb tester, I knew there was a problem.

The Beomaster 1900’s +15 VDC power supply wasn’t working. The Standby lamp remained unlit. I tried cycling the main power switch in case of a poor connection, but nothing changed.

I disconnected the power cord and inspected the +15 VDC power supply. There was no voltage across its fuse. While the fuse holders showed heavy tarnish, the unit had powered on before the restoration began. I removed the fuse and confirmed it was still good, but I still couldn’t get a reading from the fuse holders.

The following photos show the fuse holder clips and their position on the board.

These fuse holders have deteriorated with age. I then remembered that the original bridge rectifier had been replaced and that there was significant scorching on the board underneath it. It’s possible a major electrical surge occurred at some point.

In any event, I need to order replacements for the +15 VDC power supply fuse holders. If I order from Mouser today, they’ll be here on Tuesday.

This power supply issue made me consider the Beomaster 1900’s overall power input. I had previously encountered a faulty power switch on a Beomaster 2400, so I decided to examine this one closely.

I’m glad I did. The switch itself tested fine, and I cleaned it with Deoxit. However, I discovered damaged insulation on one of the main power wires supplying the Beomaster. It might not have caused any problems, but I prefer to avoid exposed wiring.

I’ll repair the power switch wiring while waiting for the new fuse holder clips to be delivered.

The following picture shows the power switch after cleaning and preparation.