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Beomaster 8000 Project

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sonavor
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sonavor posted on Tue, Aug 6 2013 8:28 AM

Here is the Beomaster 8000 that I acquired as part of an 8000 system earlier this year. I have been wanting to get this receiver working again but kept getting side-tracked. I think it is now time to dive into it. I have the service manual so I think I am set.

 

 


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sonavor
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Using a Peak DCA meter, the preamp board TR101 (BC550B) transistor measures an HFE=286 and Vbe=0.787V at 5mA.
The TR102 measures an HFE=290 and Vbe=0.781V at 5mA.

The BC550A transistors I have measure an HFE around 145 and a Vbe around 0.76V at 5mA.

The BC550 transistors I have measure an HFE around 300 and a Vbe around 0.78V at 5mA.

Menahem Yachad
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So your unmarked ones are B-grade. Most of B&O's transistors of that era are B-grade (hFe between 200-450). Choose the 2 which have the closest-matching hFe's and install those.

sonavor
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Menahem Yachad:

So your unmarked ones are B-grade. Most of B&O's transistors of that era are B-grade (hFe between 200-450). Choose the 2 which have the closest-matching hFe's and install those.

I will do that. However, it looks like it will have to be next weekend before I can get back to this. In the meantime, I am letting the Beomaster run with one of my spare preamp boards.  The spare boards have been cleaned, recapped and solder joints re-flowed.

sonavor
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I have been busy with some Beocord 8004 and 9000 cassette units lately but I took some time to change out the two BC550 transistors. The spare preamplifier board has been working great for a week now and I decided to just open the Beomaster 8000 there in the cabinet. Just swap the preamp boards and continue on was the plan. Unfortunately, with the two new transistors, I had no left channel at all. The Beomaster isn't on the bench so I can't trouble-shoot the problem. I don't feel like disturbing the 8000 system any more as I use it all the time. So I put the replacement preamp board back in and I am going to leave the working system alone for now.

I have another 8000 system I am close to starting a restoration on so I will use that Beomaster to trouble-shoot the preamp board. Before that though, I have an SC60 cabinet I have almost completed a refinishing job on. To go on that cabinet I plan to finish my Beomaster 6000 restoration. So those tasks are ahead of the second 8000 system restoration.

Here is a picture of the Beomaster 8000 opened up in the SC80 cabinet. It is so handy the way the 8000 and 6000 systems from the early 80's open up for maintenance.


sonavor
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Over the last few months I have been able to trouble-shoot and finally fix my troublesome channel loss in my Beomaster 8000.  In measuring various signal points on the preamp board I could see the problem was with that area of the receiver. It turns out the problem was with loose or bad connectors on the board. I first noticed that I could nudge P21 and P15 on the preamp board and get the dropped channel to come back.


sonavor
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I actually was certain the problem was with the P21 cable assembly so I swapped it with a spare I have. Thinking the problem was solved, I returned the Beomaster to the SC80 cabinet and was ready to enjoy the 8000 system again. After a few minutes of happiness though, the left channel dropped out.
Here is the P21 cable assembly.


sonavor
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I went back to the bench with the BM8000 once more and was determined to find the problem source. This time I noticed the P15 connector could be moved and return the missing channel. After experimenting with the P15 connector (rechecking solder joints and the cable wires), I determined that I couldn't fix it in its current state. So I decided to change both the P15 cable connector and the preamp mating connector.


sonavor
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It has now been over four weeks and the Beomaster hasn't failed since this last fix. This goes to show that being a fan of vintage audio often requires repeat visits to fully get these nice machines back to full use. 

 

-sonavor


Menahem Yachad
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Very true! Repeat visits are not uncommon.

Just proves how much they want our love and attention!

Menahem Yachad
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Very nice replacement components in there!

sonavor
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Menahem Yachad:

Very true! Repeat visits are not uncommon.

Just proves how much they want our love and attention!

Yes, demanding beasts they are. Gotta love em.

-sonavor

chartz
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chartz replied on Fri, Nov 14 2014 8:22 AM

Yes. They do require a bit of attention.

I'm picking up another BM8000 next Monday. What will I find this time?

Jacques

sonavor
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chartz:

 

I'm picking up another BM8000 next Monday. What will I find this time?



I detect that you have advanced symptoms of the Beovirus.  You finish a repair (a BM8000 in this case) and the virus instructs you to search out and find another one to repair. I am caught in that loop as well.

 

-sonavor

chartz
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chartz replied on Sat, Nov 15 2014 2:41 PM

Is there a cure for this rare desease?

Where is research standing?

Jacques

sonavor
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chartz:

Is there a cure for this rare desease?

Where is research standing?

The only known cure is extreme - You have to move to a remote island that has no electricity. Meanwhile, the research has fallen apart as all of the researchers have contracted the disease and are now actively working on their B&O projects.

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