A Pair of Beomaster 1900 Receivers for Restoration: Unit #1 Reassembly for Testing and a Power Problem

 The next step before testing the Beomaster 1900 was to reinstall the four output transistors that mount on the rear heatsinks. I had removed the heatsinks and the original thermal insulating paste. On the reassembly I like to use modern SIL-Pad thermal insulators. They do a great job and don't have the mess that thermal paste does.

Here are the parts laid out for reassembly.

I like the way Bang & Olufsen chose to mount the transistors to the heatsinks. They use curved, metal spring clips that press the plastic face of the transistor against the heatsink...sandwiching the thermal insulating material in between.

Here are the output transistors reinstalled.

Everything is installed that is necessary to start testing the Beomaster 1900.

It only took the amount of time for me to connect up the variac and dim bulb tester to try powering up the Beomaster to discover a problem.

The Beomaster 1900's +15 VDC power supply was not turning on. No Standby lamp illuminated.
I exercised the main power switch again to make sure it wasn't dirty but nothing.

I unplugged the power cord and started to check around the +15 VDC power supply.  I could not measure anything across its fuse.  I had noticed the fuse holders were badly tarnished but this unit had powered up prior to starting the restoration. I pulled the fuse and it was okay. I just couldn't get anything through it from the fuse holders.

Here are the fuse holder clips and where I removed them from on the board.

Age has not been kind to these fuse holders. I remember now that the original bridge rectifier had been replaced on this Beomaster and there was a large, charred mark under where the bridge rectifier had been mounted. It is likely some big power event had occurred sometime in the past.

In any case I need to order some of these fuse holders on the +15 VDC power supply line.  If I order them today Mouser will deliver them on Tuesday.

The power supply incident got me thinking about all of the input power to the Beomaster 1900. I had seen a bad power switch on a Beomaster 2400 in the past so I should look at this one more closely.

I am glad I did. The switch actually measures good and I did some cleaning on it with Deoxit.  However, I found a cut in the insulation on one of the main power wires delivering line power to the Beomaster.  It probably wouldn't hurt anything but I don't like bare wires where they are not supposed to be.

I will rework the wiring on the power switch and fix that problem while I am waiting for the fuse holder clips to arrive.

Here is the cleaned up and prepared power switch.