So far I have disassembled the BM and cleaned out most of the dust and debris. Here's the beast with all the boards removed and cables marked.

I'm now in the process of rebuilding the output stages (replacing caps and trimmers), cleaning and applying new thermal grease to the Darlington transistors. Here's the right output amplifier removed.

First question I have is on the trimmer replacements. I ordered Bourns 100ohm 12-turn 1/4W trimmers (PV37 Series). However they seems smaller than most of the trimmers most others are using. Would these be ok or should I really use 0.5W trimmers instead? 

Use the good old black Piher PT-10. It'll be fine for the job.

But - I really would recommend diagnosing and repairing before making any "updates" and "improvements".
The initial problem may not be capacitor or trimmer related (indeed I don't think it is in this case) - and by doing a lot of work there's a huge risk of
introducing more faults, - including faults that have no "natural" cause, - and that could make diagnosing very difficult.

THEN - do one module at a time. Adjustments and all.

Now, when you've messed with the idle current settings, you will have to set those right away (both of them!), when the Beomaster starts up (if it will start), leaving you no time to do any other diagnosing at start-up, which could have been of interest with regards to the initial problem.
If you don't set the idle currents (and DC-offsets) right, the Beomaster may not stay powered on long enough for you to do the settings, or if set all wrong it may overrun and do enormous damage to one or both output stages.
Keep an eye on the current monitor of your variac the first time you start up the Beomaster - and cut the power immediately, if the power consumption is not normal.

Martin

I would advise the same as Martin for the trimmers, PT-10 or PTC-10 for the cermet version for better thermal drift.

As for the capacitors, the red ones must go out, from past experience.  Actually, one looks dirty on top.  Might be a leaked cap or liquid with dust mixture...

I have to applaud your ambition....and the amount of work you have already done is quite impressive too. Myself I would have chased down the actual fault before going to town on the whole unit....but hey you are where you are....this is going to be an interesting project, keep the pictures and dialogue coming 🙂

Craig

Thanks Martin, 

It was my understanding that it would be wise to change the trimmers before powering up. So figured I should start with the output amplifier boards first and it would make sense to replace the capacitors on those boards as well. In fact most of the caps I checked were either out of spec or completely gone.

I'm planning to set the idle current and DC offsets with the output boards out on the workbench and refrain from making too many updates.   

krais wrote:

I'm planning to set the idle current and DC offsets with the output boards out on the workbench and refrain from making too many updates.   

Great idea.
- But how?

And I agree on replacing the caps, but they will not be the reason for the present fault.

Martin

Hi,

I use this method to do my initial restorations of the Beomaster 8000 output amplifier assemblies. I have also successfully reworked the assemblies while they are still inside the Beomaster but I have found that I like reworking boards outside the cabinet better. Besides making the desoldering and soldering work easier, a lot of the units I have come across have required a lot of cleaning (dust, dirt, debris, rust, etc.). In addition, more than one output amplifier board has required some repairs to burned/damaged traces. 

-sonavor