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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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Søren Mexico
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John, the first part of your repair and the short was interesting, but now I think you are into writing a classic how to guide. Your determination and descriptions are perfect, I will return to to this thread when I have improved my knowledge and my toll stock.

Collecting Vintage B&O is not a hobby, its a lifestyle.

sonavor
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I have been wanting to go through the tuner section tests of a service manual for a while now. It took me some time to locate and get the proper equipment but I have slowly been acquiring them (for over a year now)...although it appears I am still missing some items. I am also trying to build another test interface to compliment Frede's Classic Audio tester to enable me to run the PC audio test software on power amplifier sections.  Hopefully that will all work.

In the meantime, regarding this venture into the tuner section, I just feel that if my goal is to restore the Beomaster 8000, then I need to also make sure the FM section is performing like it should. It would be a shame to have the 8000 system sitting in my living room and have to tell people it works...except for the tuner. However, I am not declaring this tuner section bad yet. Something just doesn't seem right so I first want to be able to measure it to make sure, then see where I have to go from there.

For this restoration project I think I have three more things to test -
1. The tuner section
2. The phono section (I still haven't connected a Beogram to try it)
3. Measure the frequency and distortion of the power amplilfier section (I am missing the PC interface for that but have the parts to build it).

Menahem Yachad
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John,

A great job.

3 points here - 

Regarding the Dim Bulb tester - I'm not sure what size wattage lamp you're using, but I keep a bunch on hand, from 60W to 500W.. In this case, I would have used a 500W lamp - still gives protection, but it has to be a REAL short to make it illuminate, not just an inrush peak which it appears is what you had.

Regarding the short - I have made plenty of those mistakes, but only once, each type. There is always a new type which will jump up and bite you. Bottom line - you cannot be too careful, but accept that it does happen from time to time. My stupidity bit me most recently, about a month ago, while repairing a DVD. Be careful if you get into the new SMPS circuits - you'll need a differential scope-probe to stay safe.

Regarding the 10,000uF capacitors - in today's world, any capacitor over 3000uF can be expected to be below the rated capacitance - that's why the manufacturers cover themselves by stating +/-20%. So, my rule of thumb is always to buy the next higher rated cap, to be CERTAIN that I'll get what I really want. In this case, I'd buy 12,000uF caps, provided you can find one that physically fits. And you'll see that a 12,000uF cap will measure at about 10,400uF, which is just fine for this case.

Menahem

sonavor
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Thanks Menahem.  Yes, I checked and the bulb I was using is a 100W bulb. 

On the big 10,000uF capacitors, I am still trying to decide about whether (or when) to replace them. Three measure close to the 10,000uF and the fourth is at 8,600uF.  So I am thinking do I change just one or should I go ahead and change all four...especially if I don't really need to. I wonder if the 8,600uF cap has always measured that capacitance. that is in the 20% tolerance so it might be okay.

If I replace it I am looking at a Vishay MAL210118103E3 10,000uF replacement. It has a load life rating of 10,000 hours, is the correct size and not terribly expensive (around $24). There is also a Panasonic T-UP series (ECE-T2AP103EA) is only about $11. It is also the correct size but has a load life rating of 3000 hours. The Panasonic capacitor is rated at a 100V though while the Vishay is a 63v rated cap. The original 10,000uF caps are also 63V. I found an article at EDN.com where the author reports that for each degree the capacitor operating temperature drops, the life is doubled. The ratings on the two capacitors I listed above are at 85 degrees Celsius (185 degrees Fahrenheit).  Looking at where those Beomaster 8000 capacitors are located, I don't think they ever get close to that temperature which means their expected life should be much, much longer. If that is true, then the Panasonic T-UP series should work fine.

sonavor
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While waiting on my test equipment pieces, I was inspecting the Beomaster 8000 FM and FM Interface boards again.

In the photo here, I have marked the trim pots that look aged and discolored compared to other trim pots in the Beomaster. Is the discoloration just cosmetic or is it an indication that there has been heat and the trim pots might need replacing?  Also, I just noticed that R21 (47 ohms) on the FM board is badly discolored. It looks like I should probably pull it out and check it. The R21 resistor has a triangle symbol by it in the schematic to flag that the same type, wattage and value must be used when replacing it. The parts section lists it as 47 ohms, 1/4 Watt. Is it a carbon film resistor? Another group of components on these two boards are the tantalum capacitors (the little green components). There are ten total. It looks like four of those are in the signal path. I know there is sometimes an argument regarding whether those tantalums should be left alone or if they should be replaced with electrolytic caps.

So now I am trying to decide on whether to replace the four big 10,000 power supply caps, the FM and FM Interface board tantalums and the five trim pots that look discolored.  I think R21 needs replacing.


sonavor
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A quick update.
I pulled the R21 resistor and checked it. While it looks awful, the markings are completely gone...it actually measures 46.9 ohms. I have a replacement in my stock though so I replaced it. I also started replacing the trim pots on the FM boards.

I also pulled the two FM boards from another Beomaster 8000 (a supposedly dead unit that won't power up). With those two boards, the Beomaster project unit FM reception is good. I still can't execute the service manual measurements for the tuner for some reason but that is a different story.

An interesting thing about the second Beomaster is that the FM boards have electrolytic caps instead of the tantalums. It could be that the previous owner had the unit updated but it is odd that someone would recap the tantalum caps and not the electrolytic caps. Unless this recap was done back when this receiver was still relatively new. If that is the case, when I get around to working on this second Beomaster, I will probably do all of the caps again. I will post a picture of the new set of boards later. There were a couple of other odd differences I want to post pictures of as well to see if anyone out there has seen them on a BM8000 before.

sonavor
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Here are the two FM boards from the other Beomaster 8000. The capacitors that were tantalums on my project Beomaster are marked by bright green marks. Are they replacement caps or did they come from the factory like that?


sonavor
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The display board of the second Beomaster is interesting. It has the blue covering over the Clipping lamp. Maybe the Clipping lamp wouldn't go out like my receiver so the solution was to hide it?


sonavor
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The microcomputer board is also different. The connectors to the front panel are mounted differently and the shield box for the computer is different. On my project Beomaster, the top and bottom shield box pieces were soldered together by metal tabs that go through the board. This Beomaster has a box frame that is soldered to the board but the box has a removable lid that pressure fits in place (like the one on my Beomaster 6000). I am thinking this Beomaster is a newer unit that the project unit.


sonavor
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To compare...here is the microcomputer board of the project Beomaster 8000.


sonavor
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The second Beomaster 8000 also has something extra on the preamplifier board. I can't tell if it is an after-market add on or something stock. It is circled yellow in the picture. There are actually two of those plastic round discs, one for each channel?


Menahem Yachad
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Large Caps - Panasonic are fine.

Trimpots - replace every single last one - don't even think about it. Piher PTC-10LV - in stock at Mouser

Those blue caps look like Chinese replacements - can you read the manufacturer label?

R21 - In those days, AFAIK, the resistors which B&O used, were all carbon composition (CC), not Carbon Film (CF). If original CC resistors have failed in the POWER SUPPLY circuit, replace with CERAMIC resistors. The price of CC resistors today has shot through the roof, because of virtually no more demand, and are not worth paying the outrageous prices demanded. Ceramic resistors do everything that CC resistors did, and do it better. Never use Carbon Film in Power supplies.

sonavor
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I am using the FM boards from the spare BM8000 unit for now. Meanwhile, I have the original FM boards on my bench to replace the trim pots and check the other components. I have Piher PTC-20LV trim pots for all the values except 25K ohms. For that I bought a Bourns as Mouser doesn't carry that value by Piher.

That R21 is on the FM board, not the power supply. I replaced it with a carbon film resistor. It is only a 1/4W resistor.

Those blue replacement caps are made by Marcon. The orange replacement is a Rubycon.

Once I get the original boards updated with the new parts I will try them out again. If they don't perform as well as the two replacements I will switch the replacements back in and move on. I will revisit learning how to perform the Beomaster 8000 tuner tests later. Before that I plan on learning on some other tuners. The BM8000 service manual instructions for the tuner adjustments is just not translating well for me. I think I have the tests set up correctly but I am not seeing the expected signals (even with the replacement boards). Using the same test signals on another tuner, like a Yamaha TX-900U, I can see the tuner respond to the test signal down at a low input amplitude of 20dBuV EMF.  The BM8000 isn't responding until the signal amplitude is up over 60dBuV EMF. Yet the Beomaster is receiving FM stations so I must be missing something in the instructions. I will go off and do some homework on tuners and testing them so I will be better equipped (mentally) to try this in the future.

What about the picture I posted of the preamplifier from the second Beomaster 8000....regarding those round, inline devices on the white and blue wires. Any idea what those are?

chartz
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They look like telecom easy grip connectors don't they? Scotchlok?

Jacques

valve1
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chartz:
They look like telecom easy grip connectors don't they?

They do indeed. The telecom connecters are "insulation displacement" and are available dry or vaseline filled. Never seen a green one.

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