Beomaster 4400 Type 2419: Investigating the Power On Problem

I left off this Beomaster 4400 restoration thread having reassembled the receiver for a power on test.
That did not go as I planned and it appeared there was a problem with the right channel output amplifier circuit.

I disassembled the Beomaster 4400 partially so I could de-solder the leads to the output amplifier transistors that mount on the heatsinks.  I found two bad right channel TIP 146 Darlington transistors. That being the case I ended up checking all of the output amplifier transistors for both the left and right channels.

For reference, here are the locations and transistor types.

After replacing the two bad TIP 146 Darlingtons I was ready to try the power on test again.
The dim bulb remained off, so a good sign there, and I reached the line voltage level of 125 VAC, 60 Hz on the variac.

The +15 VDC power supply measured good as did the ±35 VDC rail voltages. Before I could continue with the other power supply measurements I noticed my voltmeters were starting to show the rail voltages going down.  They were decreasing slowly (increments of about 50mV) but they were dropping. The ammeter on the variac wasn't showing much of a current draw but something was wrong...so off with the power again and abandonment of another power on attempt.

During the power on test I noticed that the Beomaster 4400 power on lamp was not illuminating.
Before trying another test I pulled the lamp and checked it.  It was indeed burned out so I replaced it.

Here is the location of the lamp and the replacement.

With a replaced Power On lamp the Beomaster 4400 now indicates power is applied.

While that was good you can see a new problem...The Power On lamp remains on all of the time, even when the Beomaster is switched to the Off position.

Definitely a sign that there is a problem with this Beomaster 4400 On/Off switch.

So far I had only been leaving the Beomaster powered on for a few seconds.  I wanted to collect some more information regarding the Beomaster losing power.  I connected my DMM measurement tools to the transformer secondary and rectifier outputs for ±35 VDC.  When I applied power with the variac I ended up with a reading of over 52 VAC across that secondary.  Sure enough, it started to drop.
I had planned to monitor the voltage drop for a while but began to notice a wisp of smoke coming from the Beomaster 4400 Power On/Off button...power down time again.

Now things are starting to add up.
In the power supply circuit diagram here -

you can see that the Beomaster 4400 applies line voltage to the receiver power supplies entirely through the On/Off switch.

Note that this is a Type 2419 BM4400 and has a fixed line voltage for the USA.

After years of powering on and off the switch contacts start to wear and get pitted. This Beomaster's On/Off switch must have welded closed from all of the arcing during power on cycles.

Of course I will need to verify this but now I know I have to go through the steps of replacing the Power On/Off switch.

Here is the Beomaster 4400 On/Off switch.

That switch assembly will have to be removed and most likely replaced with a spare.

First however, I will remove the replacement switch from the spare Beomaster 4400 and check that On/Off switch to make sure it is in good working order.  It is a lot of work to remove these switches so I want to make sure I am replacing the bad switch with a good one.

Here is the Power On/Off Switch removal and disassembly.

These pictures show the switch on and off actuation.

You can see in the photos that there is a lot of debris from arcing that occurs when the Beomaster was turned on and off.  All of this will be cleaned along with the switch contacts.

Speaking of which....Here are the actuators removed. The pitted contact points are easily seen.

I sanded both the actuators and the four fixed contacts as part of the switch cleanup.

Now for the ordeal of removing the Power On/Off switch of the Beomaster 4400 I am restoring.