Hi,

Some previous owner made some modifications didn't they.

The original reservoir capacitors could have easily been replaced so that is puzzling.
I would remove all of the modifications and disassemble most of the insides of the Beomaster to get everything cleaned up again.
While the boards are apart you can do the capacitor replacement. I would change the trimmers as well.
Because there are sure signs of tampering you will need to look for other modifications to the board(s).

The Beomaster 4000 is a nice receiver but the 4400 is a huge improvement in my opinion.

Be aware that the Beomaster 4000 units very often have transformers that hum and buzz. They are epoxied inside but that becomes brittle over time and the humming and buzzing starts. The only way to fix it is with a new transformer. As you can see that is a very low profile transformer so you won't find a replacement for it off the shelf. Getting one from another BM4000 only buys some time. The better solution is to get a new replacement that is a low profile toroid type transformer. There are a couple of Beoworld members that repaired their BM4000 units that way. It isn't cheap though.

I would recommend removing the transformer and having it tested first to make sure it is hum/buzz free.

-sonavor

Thank you for the transformer tip, I will get on it as soon as I can.

-djagan 

Oh, it was really "got-at".

The orange capacitors at the back of the amplifier board are not bulged, I believe they looked like this from new.

Seems like someone tried to "improve" something without knowing what they were doing.
If the output series capacitors are fitted several in series, any point in attempting to improve the damping factor by increasing the capacitance is out the window.
And they left the most trouble-prone components in place.

Something to backtrack and clean up...

Martin

This one has the newer amplifierboards. Trimmers aren’t just simple to change without proper instructions, load and a scope. 

Backtrack and clean up is my only way out; totally agree with you.

I’m looking forward to this challenge and if I get over my head, I’ll just reach out to the experts.

thank you all for your insights.

Hi all:

 I have some updates to add to this modification done by the previous owner that could unravel the mysterious caps.

Those two large caps were placed between the output transistors and the speakers.

 The other orange ones were in parallel with the existing ones on the output board.

 I had a 901, 3000 and 3400 previously and they all would blow the output transistors for, what seems like no reason. I often wondered if there was a way to protect those transistors as they were not cheap at the time. Could this be a way to protect them or is this an attempt to boost the output?
Maybe the experts can shed some light on this.

dj 

I've never had an output transistor blow for no reason. If the transistors are blowing out then there is a cause. The strange modifications on your Beomaster 4000 look like some strange experiment somebody attempted.  I have no idea what they were trying to do. 

Trust the original B&O engineers that developed the Beomaster 4000. They never would have released a product if it was susceptible to transistors easily failing. You can bet they performed rigorous testing when the amplifier was new. 

Decades later when we here on the Beoworld Workbench attempt to restore these components we have seen a lot of strange cases. Many times the problems are just aging of parts. Sometimes the aging is accelerated by a poor environment the audio component was stored in. Then there are cases where someone attempted to repair/restore a component without really knowing what they were doing. Sometimes without a service manual. Sometimes with hardly any electronics experience. Those are the Frankenstein cases where you have to try and back all of the bad stuff out and try to get back to what was original. Occasionally the original parts are too badly butchered to fix.

-sonavor

I agree with Sonavor.

Never in my 40+ years of repairing B&O did I see a semiconductor fail because of age alone.
There was always another reason; Short circuit, overload, lightning strike, static discharge, moisture (bad storing) etc.

None of the added capacitors will protect anything from anything. Perhaps it was an attempt to compensate for aging capacitors, which is a real thing,
- Not that the solution would work anyways.

Boosting? No.
Improving? No.
Messing up? Yes.

Martin