ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
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.
The first thing to figure out will be why the BM8000 always shows CLIPPING mode when it is turned on (STBY to any function). Tomorrow I will open the unit up and clean off the dust.
sonavor: 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.
This will be a nice thread. Looking forward!
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http://tinyurl.com/qj9cjsf
So am I!
Jacques
I have opened up the Beomaster 8000 to inspect what sort of work I have to do on it. Starting with the back, there is a fair amount of dust but I have seen a lot worse. Once I get it all open I will clean it up and see what capacitors I need. I have the original service manual and it will give me the values but I like to check what is actually on the boards.
Display Module - 8
Lower panel in service position
After some quick cleaning, here is the left Output Amplifier Module - 5
Here is the right Output Amplifier Module - 5
Preamplifier Module - 3FM Module - 1FM Interface Module - 2
Display Module - 8Microcomputer Module - 9
The Beomaster 8000 is one of the heaviest receivers I have had to lift. I wonder how many of these units suffered damage because someone dropped them? Here is why they are so heavy. A giant of a transformer.
Power Supply and Remote Receiver Module - 6
Filter and Tone Control Module - 4
I took a quick inventory and checked it against the Beomaster 8000 service manual and boards. I think I have about half of the replacement electrolytic capacitors in my own stockpile. They are extra audio grade capacitors that are less than a year old. For the other half I will probably have to make a run over to Mouser tomorrow or Thursday. I am thinking of leaving the microcomputer board alone as it requires un-soldering the metal box. It looks like there are a couple of electrolytic capacitors in there though (a 1uF and a 22uF) so maybe I should go ahead while I have the receiver open.
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).
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 onone module at a time and check the functionality frequently. This will make diagnosing much easier in caseyou, by accident, should happen to introduce a new fault.
Martin
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?
sonavor: Do you have a suggestion on what board I should start with given the receiver powers up with the CLIPPING lamp lit up?
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 ?
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.
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.
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.
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.
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.
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).
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.
Here is the wiring for the clipping signal per the BM8000 service manual.
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.
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.
That looks pretty cool. Looking forward to that. :)
Bose home theatre systems have been a favourite among audio equipment dealers and users alike.
I checked the circuit again this morning to double check the results. The measures were pretty much the same but I have added the voltages at the collector for TR200 (on the Output Amplifier Module).
On the Display Module (8), IC4 should normally be around 50mV at the base. Currently, the right channel is pushing that to over 1 V so the lamp turns on full. With the right channel disconnected, the left channel applies right around 1V or a little less so the lamp turns on, but dim. The voltage at the collector of TR200 on the right channel is way off from the left channel.
I think I will have to pull those output amplifier modules next and check the solder points of the components. I will probably go ahead and change the electrolytic capacitors while the board is out.
Meanwhile, during my testing, the display module segments turn on and off differently between tests. I have been able to carefully put the board in and get the display functioning with all segments. So there is an issue with the board connectors. I am going to wait and work on that problem when I have the output module board and power supply boards all checked out and done since they sit underneath the display board.
No luck with the clipping lamp problem tonight. I removed the display and microprocessor boards again so I could get to the power and right channel output amplifier board. I checked and replaced a few electrolytic caps on the power and output board (right channel only). There were two 100uF caps (C205 & C211) that measured a little over 200uF. There was one capacitor that could not be measured (C206). I replaced those capacitors and a few on the power supply board.
I re-connected all the boards and tested the receiver - the clipping lamp still stays lit. A new problem occurred though. One of the wire assemblies to the pushbutton control pad came loose (broken wires). I soldered the wires back to the front panel and the pushbuttons work. However, the volume wheel and tuning wheel no longer work in controlling their respective functions. The volume control on the remote does work. The FM tuner is also not pulling in any signals. The display lights now display all segments...so at least one thing improved. I can still play a music player plugged into Tape 1. The sound is good and clear.
After a night's rest I checked the sensors for the volume and tuning wheels. I verified they are getting +5 V so I turned the receiver on and they are working now. I did reseat the connectors from the Keyboard Primary (10) to the Microcomputer (9) so I am going to assume there was a bad connection. These connectors are pretty finicky in their old age. As I said, the display segments are all lighting up properly now. That changes every time I have to move the Display (8) and Microcomputer (9) boards.
The FM tuning is still not working though. It must be some connection too as I haven't touched the FM (1), FM Interface (2) and Preamp (3) boards. I verified that everything is connected but I am not getting any FM stations. The tuning dial works and I can change the frequency on the display. With autotune engaged the output remains dead quite. When I switch autotune off, I get that white noise sound you hear when you are not on any station. So I need to trace though that part later.
For now, the receiver is playing good but the clipping lamp is still illuminated all the time. I haven't pulled any of the transistors involved to check as the boards are so touchy. Every move I make results in some problem somewhere else.
One thing I haven't checked yet is the BM8000 no load current and DC offset. I will check those next. That will mean moving the Display and Microcomputer boards to get to the right channel output amplifier but it must be done. Here is a picture of the current display with the segments all working again. That will probably change after this next test.
I forgot to post this picture from last night when I had the keyboard assembly apart. The keyboard was only partially working and I found that one of the ribbon cables and several wires that broke. The glue that holds the cable to the board had come loose with age and moving the cable while working on the BM8000 caused too much stress on the solder points. I desoldered the pins, stripped new leads and resoldered the cable in place. As I mentioned in the previous post, the keyboard is now working again. I also cleaned the keyboard assembly as there was a lot of dust in there.
I performed the no load idle (half of it) and DC offset adjustments on the left and right channel. What I mean about half of the no load idle is that the service manual says to measure and adjust the voltage across test points TP200 (R236) and TP201 (R237) to 18mV while the amplifier is cold. That part is easy to do so I did that part. The second part of the adjustment is to put my meter in series with the collector side of transistor 203. That means taking out the board, de-soldering the collector and wiring up some test leads. I didn't want to do that yet so I just did the 18mV adjustment.
After that, I let the amplifier warm up, then performed the DC offset check. I repeated the adjustments for the right channel.
The receiver still plays fine after the adjustment and I don't notice any difference in the sound. The clipping lamp also remains on. Here is a picture of the left channel no load idle, 18mV adjustment.
Here is the right channel output amplifier no load idle adjustment. I have replaced the electrolytic capacitors on this board except for the 4.7uF, 63V in the lower right corner of the board. I didn't have a replacement for that one. It is in the signal path though. I measure it and it measure about 6.5uF. I didn't write down the measured ESR value but I remember it was okay.
Here is the left channel DC offset adjustment. This is with the volume at zero, speaker load is applied and the receiver has been on for at least 30 seconds. In this case the BM8000 had been on for a couple of minutes. The right channel adjust was made in the same way.
The other board I partially re-capped is the Power Supply and Remote Receiver board (6).
I didn't replace the large axial caps. They measured within tolerance on the high side. Their ESR was good. I haven't decided if I should replace them. I was reluctant to replace the smaller axial, Phillips caps. The 10uF caps all measured close to 10uF and their ESR was around 1.2 ohms. The replacement Vishays that I installed were all right on 10uF but their ESR was 2.2 ohms. The new caps have a good ESR value but the measured value of the old ones looked better. The 1uF, 100V cap I installed measured better than the old cap. The same is try for the three radial caps in the upper right of the board.
I revisited the clipping lamp again tonight. In measuring voltages around the circuit with the left and right channel connected and disconnected I have eliminated the left channel as being part of the problem. The clipping lamp glows dim, with the same driver voltage at the base of the Darlington [IC4] on the display board, regardless if the left channel is connected or not. The right channel will drive up the intensity on the lamp when it is connected so it has a problem on its clipping circuit. However, I don't thing the right channel output board has any problem musically. It plays clean and I was able to adjust the idle and DC offset earlier. So it is just something with the clipping detection.
My plan is to replace a couple of the display board clipping circuit components and see if I can get that part resolved. I'll do the same on the right channel clipping circuit but I have to order the parts I need.
I am also going to look at upgrading the board interconnects. Maybe look for some newer, more reliable connectors as the existing ones are old and have been giving me fits. I plan on keeping the Beomaster 8000 for a long time (along with the other pieces: Beogram 8002, Beocord 9000, Beovox MS150s and the system cabinet). So I want to make repairs that will last.
I removed and tested two transistors in the clipping lamp circuit that look the most likely (based on the voltage measurements I took).One is the NPN Darlington on the Display board (IC4 - TPSA13). The base is driven by the clipping detection signal from the left and right channel output amplifier boards.Using a semiconductor tester (Peak Atlas DCA55), that NPN device is not recognized as a Darlington. The tester thinks it is low power thyristor. I tried another NPN Darlington that I have in stock and the tester identifies it correctly. So I suspect IC4 as a possible problem and found a replacement at Mouser that I will order.
The other transistor is from the right channel output amplifier board. It is a PNP transistor (TR200 - MPSH54). The semiconductor tester only recognizes it as a common cathode diode network. So I suspect that device as well. I can't find the MPSH54 at Mouser. I prefer using Mouser because there is one nearby. However, if I have to order elsewhere I will. Does anyone know of a good substitute for the MPSH54 PNP?