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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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As this picture shows, I decided to open up the microcomputer box. Due to the age of this receiver and since I am going to replace the other electrolytic caps, I want to do all of them (except the four big power filter caps) while I have the receiver opened up. There is only one electrolytic cap in the microcomputer module (a 22uF, 25V axial).


Dillen
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Dillen replied on Wed, Aug 7 2013 11:32 AM

Nice project.
Do be careful with that CPU module, work in ESD safe workspace if possible.
If you don't have antistatic workspace and tools available, buy yourself an ESD field service kit with a wrist strap etc.
Easily worth its money.

If the Beomaster is basically working or at least working to some extent, I would recommend you work on
one module at a time and check the functionality frequently. This will make diagnosing much easier in case
you, by accident, should happen to introduce a new fault.

Martin

sonavor
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Thanks, I do have an anti-static mat and strap.

Do you have a suggestion on what board I should start with given the receiver powers up with the CLIPPING lamp lit up?

Dillen
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sonavor:


Do you have a suggestion on what board I should start with given the receiver powers up with the CLIPPING lamp lit up?

Separate the clipping signal lead from the two amplifier modules to see where from the clipping signal comes.
Is the cound clean from both channels ?

Martin

sonavor
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I haven't ever tried to get sound from the unit.  When I plugged it in and saw the clipping warning I decided not to connect any speakers (I kept the speaker switches in the off position as well).  I bought the entire 8000 system (speakers, cabinet, components) from the original owner who had not used them for several years.

I will replace the one electrolytic cap inside the microcontroller module, then put it back together so nothing bad can happen to it.  Then I can put the boards back together and run the test you suggest.

sonavor
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I have a question about the white (thermal?) grease in the picture of the microcomputer module. There is a clear plastic piece laying on top of the BM8000 processors. The white grease sits on the plastic between it and the metal shield box lid. Was the intent of the grease to be for heat transfer? If so, it doesn't look like it would work all that well. On home computers, when installing the microprocessor chip and cooling fan/heatsink, it is best to have a very thin layer of thermal grease (spread evenly) to help with the heat transfer to the cooling fan (and heatsink). The way the grease is spread on the BM8000, it doesn't seem like it would be very effective in thermal transfer to the metal case. Or is the grease for some other purpose?  I am trying to decide if I should rework the grease before put the lid back on.

sonavor
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Since I have the microcomputer module open I made a quick trip over to my local Mouser and picked up the capacitors I need. I replaced the C85, 22uF electrolytic cap here. Now I will close the box back up and run the diagnostic tests Martin asked about.


sonavor
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This picture shows the BM8000 Microcomputer Module (9) with the shielding box lid open. The white thermal grease on the processor IC devices doesn't look like it transfers to the "L" bar under the lid. I will add some more thermal grease for the gaps but I still don't think that will be very efficient. I think the bar should mount so it contacts the tops of the ICs evenly. But I am not going to change it right now. If an improvement for the cooling is needed here I will look at it again.


sonavor
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I did a quick sound check with this Beomaster 8000. On both headphones and my test speakers (Beovox S55), I get good stereo sound. So the CLIPPING lamp stays on but I don't detect anything odd in the output.

I do see a couple of new problems. The control buttons don't all function but everything works via the remote control.  So maybe the button pads need cleaning. With the modules all connected back up, the displays are not showing on all segments. 

So on the clipping lamp I still need to check the signal driving it and see what is causing that to stay illuminated. 

sonavor
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Because I was seeing a good display prior to opening the receiver, I decided that my re-install of the Microcomputer Module (9) metal box must be causing the problem. I removed the top cover of the metal shield box and reconnected the module. Now the front panel controls are working again and most of the displays are working. The volume indicator has the bottom segment row out. Previously that was working so there is still some connection issue with that.

I am still getting great sound from the Tape 1 input (using an ipod Nano) and the FM tuner is working well. I am getting decent reception without even connecting my antenna yet.  Does that mean the illuminated CLIPPING lamp is a false indicator?  Something wrong in that detection circuit?  I still need to do as Martin requested and pull the wires from the left and right channel that are for the clipping detection.  The service manual says that is P38-3 of the Output Module (5).

 


sonavor
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I suspected the volume display problem with the lower segment bars not lighting was due to a short on those lines from the connector between the microcomputer module (9) and the display module (8).  That turned out to be true as the metal mount for the top and bottom shielding box lids touching the connector for the display. I unsoldered and removed that metal mount and the display started working again. However, on re-assembly some other segments of the frequency display stopped working. I am sure it is due to a connection interference problem as well. This assembly of modules 8 and 9 is very touchy and I have to be careful. 

I need to clean up those two modules so the connections are solid and remount the shielding box a better way so it still does its job but isn't so close to interfering with electrical connections.

With the connections on this unit being so touchy I am wondering if it is worth the risk of re-capping it. Right now is sounds very good. I haven't done any serious listening though. If I want to start using this receiver regularly, I would probably feel better if it is re-capped.

sonavor
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Here is the wiring for the clipping signal per the BM8000 service manual.

 


sonavor
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Here is the result for my first test of the clipping lamp problem. I haven't measured any voltage levels yet. I just tried a quick test where I pulled the P38 connector from the left channel output module (5). That did not affect the clipping lamp (it remained on).  So I disconnected the P38 connector from the right channel output module (5). That causes the lamp to go dim, but not off.  Next, I re-connected P38 on the left channel and the lamp remained dim. 

I am not sure what that means yet and I will try to measure the voltages involved.

sonavor
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Okay, here are some measurements I made on the left and right channel output amplifier module clipping detect signal and the display module clipping lamp.  The right channel seems to be affecting the lamp being on but even with the right channel clipping signal dis-connected, the left channel will cause the lamp to illuminate a little. When the left channel is the only control over the lamp, the value on the low side of the lamp is 3 V.  It should be 5 V.  When the right channel is connected to the clipping lamp control, the low side drops to 121mV.

 


huntsatulias
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That looks pretty cool. Looking forward to that. :)

Bose home theatre systems have been a favourite among audio equipment dealers and users alike.

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