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David Penny wrote:

The other one has no display at all.

The easiest way to start debugging this is to swap components between the working and non-working speaker. 1) PL cables and connections, 2) amplifiers, 3) check the soldered wires on the inside of the display connector on the bottom plate of the speaker, 4) display boards.

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The display was most likely installed upside down when a previous owner worked on the speakers and didn’t have a way to test the displays. It should be an easy fix. Carefully remove the plastic display cover. The plastic will be brittle (new replacements are available if needed). IIRC, the display is held in by 4 screws. Remove, flip, reassemble, and enjoy your new Pentas.

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marcham wrote:

When you say to avoid the urge to debug by part swapping, how would I test components properly then? In this case, I was going to try to trace the failure point from the power supply pins, where I can now detect continuity between two pin pairs, unplugging components as I test them. Is there a better option?

Apologies in advance it you already know this… What I consider “debugging by part swapping” would be something like blindly replacing any component because it might be the one causing the problem. For example, if you aren’t getting a good 5v signal, you could replace D16 to D19 with new parts. It is unlikely that this would fix the problem. Instead, I think that it is better to understand how the power supply works, then devise and run tests to verify it it is working or not. The 5v supply is very similar to that described here. Using your meter, check to see if the voltages and waveforms are what they should be. If not, the problem could be in the circuit or external to it. Isolating the power circuit would be the next step. I would start by removing connector P2 and verifying the output of the rectifier and transformer. If that checks out, remove P2-2 (pin2 2 of connector 2) and reinstall the connector. This isolates most of the 5v power supply from the external circuit (it also provides a convenient place to measure 5v current draw later). Retest the 5v power signals. Still no joy? The problem must be in either the power supply circuit or reset circuit. Lifting a leg of R75 further isolates the power supply from anything else. If the power supply still doesn’t work, there are only a couple of parts that could be the problem and it should be pretty obvious which one(s) based on the meter readings. Now is the time to start removing, testing, and possibly replacing individual components (based on data instead of hunches). I purposefully went into painful detail here to illustrate an approach that is based on 1) understanding how the circuit works, 2) measuring to verify proper operation and 3) isolating the circuit for ease of debugging. Also, note that there was a minimal amount of soldering involved. Much of what I described above is implicit in the advice that you got from others. Hopefully my explanation provides insights into why things are being suggested.

Based on your posts it sounds like you are getting more serious about this hobby. Check out the Digilent Analog Discovery. It might be useful to you. In general, anything that it does can be done better with dedicated bench equipment. However, everything that it does, it does well and is often all that is needed.

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marcham wrote:

I’ve decided to upgrade my equipment to a proper multimeter with capacitance testing, grab a small component tester, and an ESR meter. Hopefully, this will help me track down the problem with greater ease, following the schematic.

Also, magnification and lighting is often overlooked as a debugging tool. I bought a stereo-microscope (a.k.a. inspection scope) to help me do SMD repairs. I was surprised to learn how useful that it was for debugging through-hole boards like what are in the BG8002. Careful inspection under good lighting can easily reveal solder bridges, cracked solder joints and traces, stray solder balls, bent and shorted component leads, etc. I consider the usefulness of an inspection scope to be right up there with a oscilloscope or multimeter.

Of course, even a decent, Chinese made (relatively inexpensive) stereo-microscope, like the Amscope, is cost prohibitive to most hobbyists. Alternatives are taking pictures with a camera (macro mode if possible) and viewing the pictures on a big monitor or USB microscopes that display on a big monitor. Scanning the board on a flatbed scanner and (you guessed it) viewing the results in on big monitor can also be very helpful if the scanner has a good depth-of-field.

The advantage of a stereo-microscope over the alternatives is that one can do live work under magnification without losing depth perception.

On a related note… I thought I was “really good” at soldering until I went back and examined my old work under the microscope. My work wasn’t that bad, but has definitely improved now that I can really see what I am doing.

I suggest that you really carefully inspect the boards for “mechanical issues”.  Look for cracks, bridges, and now, places that may have been overheated. Go over the boards inch by inch. Inspect everything, not just where you worked. Avoid the urge to debug by part swapping. Every time one removes and replaces a part there is a chance of damaging the circuit board, even if good technique is used. Test any new parts before installing on the board, especially Chinese made ones or any components that could be counterfeit.

Don’t hesitate to ask if you have questions on interpreting the schematic or don’t understand how a circuit works. There many here (including myself) that would be happy to help. There are also many other general electronics repair resources out there. My experience with B&O equipment is that the basic circuitry isn’t much different than anything else out there. However, there is usually “more of it” to support the “B&O magic” features and there can be interdependencies that aren’t obvious. The good new is that if you can fix the basic functionality (like a light sensor not working or a switch not making contact, etc.) the interdependencies usually take care of themselves.

I wish you the best of luck with your repair.

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Another possibility is to try a 250mA fuse (if it is available locally and you don’t want to wait). The worst that could happen is that the new fuse blows unnecessarily. However, I can’t recall that ever happening when I’ve done this. There is usually somewhat of a “safety factor” when fuses are sized to avoid nuisance tripping.

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Mark-sf wrote:

if you have put in one or more of the electrolytic caps backwards and tried to turn it on, you’ll need to check the fuses, transistors and regulators prior to that as you have effectively shorted them

Don’t forget about checking the capacitor that was installed backwards. (don’t ask me how I know)  😉

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As far as the polarity for C24 goes… One way should work normally, the other will likely make smoke. It should be obvious which way you have ;-).

edit: Upon closer inspection of your pictures, it appears that two configurations shown are electrically identical since you rotated the capacitor 180 degrees when you shifted it in the mounting holes. The same mounting hole shift without the rotation is the recipe for smoke. 😉

As far as the pins and probes goes… The 5v regulator is a standard 7805. Downloading the data sheet should give you all the info that you need. Based on the BG8002 schematic, you could also measure the input and output voltages for the regulator on connector P2-5 and P2-2, respectively.

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marcham wrote:

Another oddity that I noticed with this cap is that the board diagram shows reversed polarity compared to how the original was installed.

I don’t recall the exact details of this, but the “apparent polarity” of the capacitor (as viewed from the top of the board) changes depending on whether one uses the wide or narrow mounting holes. Most of the time, one can simply match the orientation of the stripe on the new part to that of the old part (as viewed from the top of the board). However, this board has an unusual arrangement that needs special care.

The negative pad of the primary hole is connected to negative pad of the alternate hole by a trace that snakes around and a jumper wire on the top of the board. It is hard to explain in plain text. The important thing to note is that the polarity marking on the back of the board is correct and the capacitor should be installed to match.

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marcham wrote:

I think a component may have failed from excessive heat (I mentioned my solder station issue before), and I wonder if a cap has gone.

You are correct to be worried about excessive heat. Capacitors are more tolerant of overheating than transistors, diodes, or ICs. The solder pads on the circuit board are also sensitive to being overheated. The big issue with the pads is that the effect is cumulative. Every removal/replacement of a component puts the pad at risk. This the main reason that I suggested practice. Being able to solder and desolder quickly and cleanly is the key to avoiding damage.

For the voltage debugging… Get the schematic, start at the transformers, and check the voltages from there. The power supply circuits are pretty straightforward. Be aware that there are a mixture of AC and DC voltages.

Are you sure that C24 is installed correctly? There are multiple sets of holes for that part and the capacitor polarity marking on the circuit board could be misinterpreted depending on which set that you used.

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marcham wrote:

I’ve included a photo; let me know if that’s what you were communicating.

How you installed C27 is correct now.

Beogram 800X’s are usually straightforward to repair. Replacing bad fuses and fixing cracked solder joints is usually the first step. Then check the important voltages (i.e. power supplies). Replace any capacitors related to improper voltages. This will usually get the machine running again or at least showing significant signs of life.

Getting specific advice on why your Beogram will no longer power on will be difficult. Advice like you found on Beolover’s site are usually intended for machines that have died naturally.

Since your machine had signs of life before the recap, I would concentrate on fixing cracked solder joints (usually on the cable connectors) and checking your work. I don’t want to sound harsh, but the soldering in the pictures could use significant improvement. It might be worthwhile to buy a “soldering practice kit” to up your game before attempting to do further repairs. Build the kit, see that it works, remove all the parts, then rebuild it again. Watch some YouTube videos to get tips. I noticed the missing solder pad for C20. This is usually an indication of someone that is struggling. It is likely that your machine can be salvaged, but the more damage that you inflict on the machine with bad soldering techniques, the harder that it will be to repair. Pretty solder joints aren’t just for show, there is a structural aspect to it that ensures long term connectivity and reliability.

Once again, I hope you take my advice in the spirit of giving you the best chance at a successful repair.

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Evan wrote:

I think generally speaking, most average folks expect speakers to be big and heavy. The 50 is big and heavy. It is a speaker.

My premise is that dedicated hifi systems have lost popularity with the general population. As such, perceiving something as a speaker may not be the first conclusion. The Beolab 50 has an arguably utilitarian shape. One could imagine a very stylish version of other items being the same shape.

I don’t think that this could be said for most of the other B&O speakers. What else could the Beolab 5 be? The only thing that I can think of is some sort of abstract art. But art usually doesn’t come in pairs.

On a tangent thought… What if Leonardo painted two copies of the Mona Lisa and they were displayed side by side? Would people still be talking about “the smile” or something else entirely?

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marcham wrote:

Is it correct to assume that between the two points connected with a blue line, I should install a wire? Then, install the cap in the two remaining holes (old center hole and the top hole)? If this is correct, should the positive leg be in the center hole? I thought that’s how the old cap was installed but these instructions seem to say that the negative leg goes there

The way that I usually do this is to install the positive lead into the center hole and the negative lead into one of the (blue) holes that needs the jumper. The negative lead should be long enough to bend over to the other (blue) hole to act like a jumper. Just make sure it doesn’t short anywhere on the backside of the circuit board.

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Beofile7 wrote:

They just see “a pair of speakers?”

Maybe, maybe not. They could be wondering why someone would have, not only one, but two, really fancy garbage cans in their living room. This would be especially true if you opted for a hidden wire installation. Asking about it wouldn’t be polite.

Of course, I’m (mostly) joking. I think that the Beolab 50 is one of the best styled speakers that B&O has ever made. However, B&O may have done “too good” of a job making them look “not like a speaker”.

I suspect that the lack of comments is more a function that high end stereos are simply not important in the current pop culture. I have many different high end stereo systems in my house. Some modern, some vintage, some tastefully blend with the decor, others are borderline obnoxious. I rarely get asked about any of it unless my guest is a hifi geek.

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Aladdin wrote:

<snip> I managed to find a wire diagram which is uploaded below which gave me some understanding. <snip>

any thoughts?

The datasheet for the STK amplifier module may give you clues about how to hook-up the amplifier board. It is usually worthwhile to examine the datasheet example circuits since it is common for OEM’s to implement them exactly (or very close). Make the STK module happy and you will have sound.

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Elephantsintheclouds wrote:

1. Copper ink pens for drawing up and closing connections on pcbs

I don’t think that conductive ink pens are good for this kind of repair. The conductivity of the repaired trace is questionable. I prefer solder bridges for small, low current gaps, copper wire reinforced solder bridges for larger gaps/current, and bypass/jumper wires for really bad or high current traces.

garibaldi70: Getting your BL1’s working again may be as simple as repairing the corroded traces. I hope you can find a good repair technician. Finding someone that is willing and able to do the repair might the hardest step in the process.

Consider practicing on something less valuable if you want to try the BL1 repair yourself. A good candidate for practice is any piece of working electronics that is destined for the recycle center or trash. Intentionally cut some traces, then try to repair them and see if the device still functions when you are done. This is also a good way to practice on removing and replacing parts.

Be warned that a botched repair is much harder to fix than something that failed naturally. I know that as a (serious) hobbyist that I try to avoid anything that was previously worked on by an amateur. I assume that many repair shops feel the same way.

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Were the schematics for the Beolab 1 ever released?

It seems like the need for secrecy, for both the OEM and secondary repair businesses, has long passed.

garibaldi70: In your 8845 picture, it appears like the corrosion may have eaten through the copper traces. Cleaning these with something like a scratch pen would be one of the first steps in debugging. This kind of repair, and Class-D amplifiers in general, can be difficult if you don’t have the proper equipment.

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ummagumma wrote:

What software are you using to parse the signal & generate those graphs?

I use a dedicated audio analyzer and use the software included with it. Prices and quality of audio analyzers vary greatly. Testing with general purpose test equipment and post processing the results is also a viable alternative. The price and quality of the general purpose equipment also varies greatly. What is more important than the price/quality of the particular equipment is that one understands the limitations of it and uses it accordingly.

Have you ever gotten a flat result out of a RIAA preamp circuit?

Everything is flat if you zoom out enough. Nothing is flat if you zoom in enough. I don’t worry that much about the “flatness” of vintage equipment. The “tonal coloration” of the old equipment is part of the charm that makes it interesting. I concentrate more of having the left and right channels match.

Maybe by the time I get this rebuilt I’ll try analyzing some parts of the circuit like that.

I try to repair the equipment just enough to get it working reliably. This usually consists of fixing the broken solder joints on the edge connectors, ensuring that the power supply voltages are correct, and adjusting the bias currents. I then do a baseline performance test (i.e. the “before” test). You can learn quite a bit at this stage. Sometimes this test reveals a specific issue that needs to be fixed. Other times, it reveals that a 60 year old piece of equipment is remarkably close to its original performance specification. It is much easier to do the “before test” before you swap all of the capacitors ;-).

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The curves above are for just the RIAA stage.

You are correct in thinking that adding more stages would complicate any analysis. Testing smaller subsets also allows one to tailor the test to the component being tested. For example, testing the power amp stage is a quite different test than testing the RIAA or pre-amp stage.

I prefer to be data driven when doing repairs and modifications. I don’t think that there is anything particularly wrong with the swap parts and listen methodology if one likes the results. I just think that I reach my goals more quickly and with more confidence with test data.

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The green/red colors are for the left/right channels. The test is of a series of (nearly perfect) RIAA weighted sine waves being fed into the circuit board and the output measured. Each vertical line is the result at a given frequency. All of the bars at the same height would indicate that the circuit perfectly implements the RIAA curve.

The deviation from a flat response is the “tonal coloration” of the circuit. Differences between the green and red curves indicate that each channel has a different coloration.

This kind of plot can really highlight differences between circuits or issues within a given board. For example, the second plot was for a board that was recently recapped using fresh, high quality Panasonic electrolytic capacitors. This shows that you can’t just blindly swap parts and expect perfection. There may be variation in the new parts or another underlying issue in the other components. Another example would be if someone suggested component values based on the first circuit and you were working on the second circuit. I wouldn’t even want to try to guess what the final result would be.

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The above plots are of the “deviation from ideal” for the RIAA amps of two different Beomasters. Areas of “improvement” could be to better match the curves to the ideal curve, make the left and right channels match better, or try to match the curve to a particular cartridge. Regardless of what your goals are, one will need a way of measuring the circuits to know if you achieved them.

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