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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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sonavor replied on Sat, Aug 24 2013 11:19 PM

hamacbleu:

... What about the two small 180 ohms resistors linking the power supply to the rectifier, just at the right of the startup board? Mine was burned.. (the one linking the red wire). Don't know if the cap caused this however...

That is a different transformer than the one that supplies the 5V and +-15V power. That is up on the +55V and -55V rail supply. I haven't checked that but I will just to finish checking the power. 

sonavor
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I have been checking components in the -15V path before the regulator and after. I had measured -26V at C34 (2200uF) so I was pretty sure D3 and D4 were fine but I measured them anyway.  I also checked the IC9 Darlington at the input of the -15V regulator.  It measures okay out of circuit.  I went ahead and checked C38, C40, D9, D8, R39, D14 and TR18.  I couldn't find any faults.  I didn't go over to the modules that get -15V (from P46 and P53). 

So I am considering putting the components back.  Using my last -15V regulator and leaving P46 and P53 disconnected (as well as leaving the speaker switches off).  That will verify the circuit before the regulator is good. I also checked the -15V regulator to make sure all three contacts were isolated from each other and the heatsink it mounts to.  No problems detected there.

Here is a diagram that shows the -15V components I have checked so far.


sonavor
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I installed my second (and last) spare -15V regulator.  I checked all of the power supply components the precede the -15V regulator and they all checked out good. So I put them all back along with the new regulator.  After that I re-installed the power supply board and connected almost everything back up. What I did not connect were the three power supply connectors I suspect the fault to be from.  Those are P51 (the connector to the +-55V rail relays), P46 (-15V power to the preamp board), P53 (-15V power to the filter and tone controls board).  I kind of suspect P51 as the most likely. If something went bad in the relay that could affect the IC9 Darlington on the power supply board.  That same node sends -24V to the -15V regulator input and to one of the relays for the +-55V.  If that relay control took the regulator input to a voltage less than the output, would that take out the regulator?  In any case, I think I can say the problem is in destination of one of those three connectors.

Here is a diagram of what I currently have disconnected.


sonavor
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The Beomaster power supply is doing fine with the three connectors I have left disconnected for now. The 5V, 15V and -15V regulators are working good. 
Today I decided to look at the start up module [7] that is the destination for the power supply connector P51 that I have removed.  That connector controls the start up relays the allow AC voltage in to the large Beomaster transformer that supplies the +-55V.  With that disabled and no -15V to the preamplifier board or the filter control board, my -15V regulator is still alive.

I checked the 5.6 ohm, large resistors on the start up module as well as diodes D1 and D2.  Everything measured okay.  I also went ahead and checked the two 180 ohm resistors (30R1 and 30R2) that the +-55V power goes through to get to the power supply board (connector P50).  Those look okay.  I haven't tested the 30D1 and 30D2 rectifiers yet.

Here is a picture of the start up module.


sonavor
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I put the BM8000 power startup and power supply back together again and verified I am still at the same place. The 5V, 15V and -15V regulators are all good with everything except P46, P53 and P51 connected. After verifying that the start up components look okay, I am having trouble figuring out how a failure in that path would take out the -15V regulator.  I am not seeing the connection. So I left the 30D1 and 30D2 rectifiers alone (I didn't pull and test them).

The +-15V supplies power to a number of opamps on the preamplifier board and that power comes from the P46 connector on the power supply board.  I decided to risk the -15V regulator and plug the P46 connector back in.  So far that test is passing and the regulators are still good.  Tomorrow I will reconnect the P53 connector on the power supply board.  That goes the filter control board.  I have a feeling it will test out fine too.  If it passes, it will take me right back to the P51 connector and to the start up circuit. It seems like if there is a problem down that trail, it has to involve the +-55V rail voltages and the power amplifier boards.  But I haven't found the relationship there to the -15V regulator.

...a lot of ifs so I will just have to try one connector at a time with the startup connector being last. 

sonavor
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sonavor replied on Tue, Aug 27 2013 12:34 AM

In my previous post I connected up the power supply board connector to the Beomaster preamplifier board. I accidently referred to the connector as P53.  It was actually P46.  I corrected the previous post so it does say P46 for the preamp connector.

Today I connected P53, the connector to the filter control board. Testing the BM8000 functions with that connected was successful. I still have 5V, 15V and -15V as I sequence through Phono, tape and FM. 

So that leaves the last connector, P51. It will probably be tomorrow before I can get back to my bench. Once I connect that connector, the Beomaster will be able to get +-55V on the output amplifier boards.  I have been here before. I do have a few more -15V regulators now (they are less that $1).   I also plan to connect my scope to the input and output of the -15V regulator and see if I can catch any failure event.  For the first step, I will leave the speakers disconnected and just test the voltages with all of the connectors (P53 included) connected.  If that goes well I will check the amplifier section with headphones.  If that test passes I will try a speaker load. Note that I haven't replaced any components in this path (P53).  I removed, measure and re-installed some components on the start up circuit but that is all.  So I am expecting something to take out the -15V supply again. I just hope I can catch and figure out the source of the problem.

sonavor
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I went ahead and tried the start up circuit connector (P51). There is still something wrong in that path. Fortunately my -15V regulator survived the single test I ran.  Prior to the test I checked the -15V regulator input and outputs with my scope just to make sure I had everything setup to catch the problem. I tried a single trigger for the power on and then again for the power off (opposite edge of course).  I was hoping then to re-connect P51, turn on power, go into Phono mode measure -15V, then catch it going off.  However, when I pressed the Phono mode everything goes to fast.  The start up relays for +-55V click on and off as the Dim Bulb Tester goes bright (then off).  I still had my scope in auto trigger so I didn't catch the event.  I disconnected P51 and went back into Phono mode.  The -15V was still there.

It appears that when the Beomaster tries to get the +-55V rail voltages going, it is forced to immediately shut the startup relays back off.  Since the Dim Bulb Tester goes on bright during the event I think that is telling me something is shorting out.  I need to find a way to remove the +-55V path to the destinations (output amplifier and power supply +-30V). That would help isolate the problem to either before or after the +-55V is created.

sonavor
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I removed the +-55V connections from the two output amplifier boards and from the power supply board (P50).  I am thinking that will eliminate those parts of the circuit from being suspect in the power problem. With those connections removed, when I try to turn on the Beomaster, I still get a flash on the Dim Bulb Tester and kicked back to standby. So the startup circuit relays try to engage but immediately click off.  Does that mean I have a bad relay?  Can it mean the IC9 Darlington that provides -24V to the -15V regulator and the RL2 startup relay has a problem driving both? 

Here is a diagram that shows where I have the power disconnected on this latest test.


sonavor
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I went through the task of disconnecting the AC wires from the 30D1 and 30D2 rectifiers.  Then I was able to check the diodes.  Both sets were 0.44 across PN and open the other direction.

I am thinking though that I should have left the AC wires off the rectifiers for a while so I could see if I can engage RL1 and RL2.   

RaMaBo
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RaMaBo replied on Tue, Aug 27 2013 9:43 AM

Hi,

 

do you have the Beomaster 8000 Technical Product Information here from this side downloaded? There are very interesting details about the function of several parts of the different circuits in the Beomaster.

Try starting the beomaster without your dimbulb tester, maybe this helps to get the BeoMaster running. The switching on of the big transformer is done by the microprocessor and the two relays to reduce the input rush current when the trafo gets powered. This might interfer with your dim bulb tester.

Ralph-Marcus

sonavor
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Well, this is interesting.  Maybe my measurement of 30D1 and 30D2 isn't correct.  I decided I did want to see if the start up circuit relays RL1 and RL2 were involved in the problem.  I felt that RL2 might be because it gets power from the same source as the -15V regulator...and that regulator has failed twice now.  So I went back and disconnected AC from the 30D1 and 30D2 rectifiers so no power is coming in through that 30T2 transformer.  That means relays RL2 and RL1 can engage without really connecting anything.

With that test set up I still left the P50 disconnected but and I connected P51 (the connector I found was related to the problem).  I was able to turn on the Beomaster and the Dim Bulb Tester remained dim.  The start up circuit relays clicked.  That points back to 30D1 and 30D2 rectifiers.  I will measure them again but they appeared to measure the same.  Should I suspect one of the big 10,000uF capacitors?

sonavor
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RaMaBo:

Hi,

 

do you have the Beomaster 8000 Technical Product Information here from this side downloaded? There are very interesting details about the function of several parts of the different circuits in the Beomaster.

Try starting the beomaster without your dimbulb tester, maybe this helps to get the BeoMaster running. The switching on of the big transformer is done by the microprocessor and the two relays to reduce the input rush current when the trafo gets powered. This might interfer with your dim bulb tester.

Yes, I was wondering about interference by the Dim Bulb Tester.  I know on the Beomaster 6000 (the newer one), that the Dim Bulb Tester prevents it from working.  However, I was wanting to make sure I don't really have a short before I take it out here.  Also, so far, most of the circuitry appears to function okay with the Dim Bulb Tester in the last few days.  As I said, I just wanted to make sure there isn't a short somewhere that might damage some other components. 

I do have the service manual and technical manual. I will go through it again.

sonavor
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sonavor replied on Tue, Aug 27 2013 10:23 AM

I checked the rectifiers again and I think they are good.  The four 10KuF power capacitors measure okay although three are between 10K and 11K with the fourth one measuring 8600uF. 

I guess the next step is to connect everything back up and try power without the Dim Bulb Tester in the path (I can hear voices in my head about another Dim Bulb if this turns out to be my issue).

sonavor
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I have a working Beomaster 8000 again. I would declare success but it is more of a recovery from a blunder so not much glory there.

However, I would like to give a big thanks to Ralph-Marcus for bailing me out of my lapse in knowledge. The Dim Bulb Tester is highly useful but it has limitations and can't be used everywhere. So far it has bit me on the Beogram 8002 and now the Beomaster 8000. On the Beomaster 6000 (types 225x), the receiver wouldn't power on with the Dim Bulb Tester in circuit so I discovered early that it couldn't be used there.

Today I reinstalled the 30D1 and 30D2 rectifiers and reconnected all of the places I had disconnected (P50, P51, power amplifier +-55V).  I checked that the Dim Bulb Tester had the bulb out of the circuit and I powered the Beomaster up.  The first test was to just see that I could turn the receiver on.  The speaker loads were off.  That worked so I tested the receiver with headphones.  That worked and I continued to the speaker test. The sound is back and it still sounds good.

So now to regroup where I am at.  This Beomaster had a problem where the Clipping Lamp would always illuminate even though there was not a clipping condition present. That turned out to be a couple of bad transistors.  During the recap process I found a few out of tolerance electrolytic capacitors.  So far I have recapped the two power amplifier boards, the power supply board, the display board, microcomputer board and the preamplifier board.  I replaced the 10uF capacitor on the 5V regulator which was, of course, the place I made the horrible mistake of not noticing the Beomaster was only in Standby and not completely off. That led down the whole messy power diagnostic exercise after my -15V regulator failed for some reason.  I am the type that always looks for a bright side. Two things came out of the mistake - I learned a lot about the Beomaster power sections. I also learned to not get complacent and always triple check my recaps.  That is because I did have a second blunder and that was the electrolytic capacitor on the power supply board that I had installed with reverse polarity. Amazingly it did fail hard over. It puffed up a bit but my short-circuit blunder allowed me to find and fix the incorrectly installed cap.

What is left now is the recap of the FM, FM Interface and Filter/Tone Controls boards. I don't know if I will have to change out any trim pots on those boards. Visually, a few look like they might need replacing but I am not sure they need to.

 


RaMaBo
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RaMaBo replied on Wed, Aug 28 2013 9:02 AM

Learning by doing can be very effective Smile

So finally the beast is working again

the one elco in the 55V power supply section reading about 8000µF could be replaced too to get the job very well done, It's nearly out of tolerance this could be due to high temperature and age. If you find a elco with about 10000µF and the correct voltage (or a bit higher) and with the same size (maybe a bit smaller) you could change this one too. Saves you same trouble in a few years maybe.Wink

 

Ralph-Marcus

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