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Graham,

I usually try to start with pictures of the component side. There are often issues with the components blocking the board markings and sometimes depth-of-field. The trace side usually doesn’t have these issues.

For boards that are hard to get out… I just think of this as being unavoidable. One needs access to the trace side to do most repairs. I usually remove the board unless the board is really accessible. This helps with avoiding soldering mistakes that might damage the old, delicate traces. Also, often the boards aren’t as difficult to remove as it would initially appear.

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[Glitch]

Graham,

I don’t have a layout diagram, but there are alternatives if you cant find one.

It is often easier to find a numbered component from the markings on the back side of the board.  If the print is too small to read, the board can be scanned on a flatbed scanner and enlarged on a computer monitor. If you don’t have a flatbed scanner, taking a picture with a regular camera can also work. Once you have the board in digital format you can also mark it up in something like Photoshop or print it and add hand notes to the printout.

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Beo911 wrote:

after having spent decent money on BL90’s and a BS Theatre you’re satisfied with that solution?

That looks like something that I would do. Especially if I couldn’t find something that exactly met my needs. I’ve had some of these temporary/placeholder solutions in service for years until I found the perfect solution.

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Actually, Craig suggested that the issue lie in the mute circuit. I merely made a suggestion of how to prove or disprove his supposition. Also, if the problem wasn’t self-inflicted, the debug path that Martin was trying to lead you down WOULD have led you to the solution.

BTW, the issue was likely more related to the ESR of the capacitor than it being polarized.

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notwist wrote:

That one would have a higher value, likely 10uF. Can you confirm this?

Per the schematic, 5C15 is 4.7 uF.

I don’t have any other specific suggestions on what to try next. I will usually make enlarged copies of the relevant sections of the schematics and make notes on it (voltages, if something seems hot, etc.). I try to capture anywhere where B&O calls out a test point since if it was significant to the engineers at B&O, it is likely significant to me.

I would also recheck for cold solder joints and cracked circuit boards. Sometimes removing the board is the only way to be thorough. This also has the advantage in that one could take digital images of the board and inspect an enlarged image on a computer. I usually use a camera to take close-ups then stitch the images together to get a lot of resolution. I have also used a flatbed document scanner for this.

This might be a good application for using freeze spray? I don’t use freeze spray myself since I would rather debug using a FLIR camera. Maybe others can comment on this?

I’m still curious on what the actual voltage is on TP14 when the machine is cold and when it is warm and muted.

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When I mentioned 5C15, it was more of a rhetorical question relating to changing the type of capacitor in a circuit where the capacitor’s ESR might be significant to how the circuit operates. I see that there are other 1 and 2.2 uF capacitors in the muting and tuning circuits. Did you change these from electrolytic to film, or just the capacitors along the audio signal path? I’m not sure if it would make any difference in this particular case, but it might be a detail that could help explain things.

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Glad to hear that you are making progress…

notwist wrote:

Capacitors were all changed into film caps

Does this include 5C15? Did you inadvertently change the timing characteristics of the silent tuning circuit?

The figure showing the relationship between the TP14 signal and the Mute signal could be a clue.

TP14 moving into the range of -2v to -5v would partially enable the mute functionality.

I’m also very curious to hear if this is on just FM or also on the other inputs. I keep an old portable MP3 player on my bench as a source for doing quick tests like this.

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It seems unlikely that R40 has anything to do with your issue. If R40 triggered the fault circuit, it would open a relay and power would be cut to the +-35V rails. You would get a “relay click” then no sound at all.

It also seems unlikely that the muting circuit would kick in partially and gradually, but it is theoretically possible that the mute FETs get into a partially biased state. You could also monitor TP14 over time. I assume that you have a service manual since it is available online, but if you don’t you can refer to the table posted by hcraig244. It implies that the TP14 is normally a negative voltage and the circuit will mute if it goes positive. I still think that it is unlikely that this is your issue, but IF you can positively rule it out it will be one less thing to consider.

It could be very helpful for those trying to help if you could post data on the actual readings that you are measuring. For example, if you posted that TP14 was -12.0v, -12.1v, -12.2v, -11.7v, -11.5v, measured at a cold power-on and 10 minute intervals, it would be more helpful than saying that “the voltage was good”.

I guess if there is a bright side, it is that your issue is repeatable. Intermittent issues can be much harder to solve.

“When you have eliminated the impossible, whatever remains, however improbable, must be the truth.” – Sherlock Holmes – Sir Arthur Conan Doyle

This context wasn’t the intent of this quote, but it sure seems relevant.

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I doubt that the mute circuits themselves are the problem. The probability of two circuits failing in a symmetrical manner is very low. For example, the FET in one of the mute circuits could be leaking, causing an unintended muting, is possible. But the same thing happening in the other circuit happening the same way at the same time is unlikely. The fault is more likely based on a common mode issue. In the case of the muting circuit, it would be the FM mute signal or the voltages powering the circuit. This line of thought also applies to things like the preamp, etc.

The reason that I suggested removing TR108/TR208 is that it would be a quick way to eliminate (or confirm) the mute circuits (and the FM mute signal) as the source of your problem.

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Here is the signal mute circuit. The signal coming in to R244 comes from the FM circuit. If I am interpreting this right, removing TR208 should disable the mute signal as a test.

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9_LEE wrote:

Still… B&O are trying to be hip, which is at least an effort. ?

Like Adidas/Gap were trying to be hip partnering with Ye? Sometimes things don’t turn out like were planned. I don’t think that this will go bad for B&O, but you never know.

9_LEE wrote:

Please don’t confuse these with ‘real case’ NFT’s which will come when we fully adopt Blockchain technology.

I think that NFT’s could be a very useful technology if applied properly. Using them to try to create wealth from something of questionable value probably isn’t the killer application. #tulipbulbs

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notwist wrote:

If the 15v rail is failing, my question would be why? I’ve not often seen a failure on a power rail without some serious damage. And it would also stay broken, not degrade with time?

The voltage could drop due to the voltage regulator overheating (i.e. bad thermal connection to the heat sink), or the system drawing more current than the regulator can provide (i.e. some other device drawing too much current), or a combination of both (i.e. high current draw causing the regulator to overheat). The device wouldn’t have to completely fail. Think of it more as going into a self-protection mode.

Have you been monitoring the output of the Overload Circuit? Could it be something as simple as a bad light bulb in the circuit causing it to work improperly?

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My interpretation is that most of the negative comments on this topic are based on people really caring about the company. When they see something heading in the wrong direction (from their point of view), they get upset.

I don’t know how NFT’s will play out over time. There have already been documented cases of NFT’s being outright fraud. Many believe that NFT’s are based on the Greater Fool Theory. I’m a bit less jaded and put them in the category of conspicuous consumption.

Regardless of the where NFT’s are heading, it is the effect that they could have on a company’s reputation that concerns me. These newly issued NFT’s are likely to be as legitimate as a NFT can be. However, if enough of the NFT’s issued by other sources go bad, then B&O will be guilty by association. In business, reputation is everything, and should be fostered and defended vigorously. It is surprising to me that B&O would take a risk like this.

Ultimately, I think that how this is viewed will depend on the issue price. If the prices are low, and the B&O NFT’s are viewed like fun little tchotchkes, then it is a cool marketing ploy. If they are offered at investment level pricing, then the reputation risk goes up.

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Aren’t NFT’s the modern way of doing this?  😉

I’d rather have the bottle opener.

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Is the thermistor R40? If so, the service manual calls it out as “50 0hm 30% PTC”. You can test it by removing it from the circuit, hooking it to an ohm meter and observe the resistance as you heat it up with something like a hair dryer.

I would also make notes of all of the voltages from the power supply and see how they change with time and temperature. From the schematic, it appears that many of the voltages are referenced from the +15v supply. If this dropped down, many of the other signals would follow.

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Maybe you can work out some sort of “swap” with the seller to save money? (Might not work due to the cost of shipping)

[Glitch]

Have you checked the thermal compound and mica insulators?

Sometimes, the thermal compound is fine after decades, other times it has dried out and shouldn’t be trusted.

Mica insulators can split between layers. These will look like there are air bubbles in the mica. Mica is a good thermal conductor, air is a good thermal insulator.

Disassembling, inspecting and replacing the thermal compound with modern, higher performance compound doesn’t take that much time. Even if it wasn’t needed, it can provide peace of mind.

Addition:  The above comments are primarily targeted to the power supply components. These might affect both channels simultaneously. Also, if you have a FLIR camera, it is really useful for debugging potential thermal issues.

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It might “work”, but you should be cautious. The outputs of the transformer will be “off” by the same percentage as the percentage difference of the input voltages. This likely won’t affect any regulated DC signals, but will affect unregulated AC signals. You would have to carefully study the schematic to understand the ramifications.

I would be more concerned about the liability associated with such a modification. If this modification caused a fire in your home, would your insurance cover the damage? What happens if the receiver is sold and the next owner has an issue? If you swap out the transformer for the proper one, you would have an easier time justifying the change.

Personally, I would look for someone parting out a similar machine. In general, there isn’t much demand for transformers since they typically don’t go bad. When people part out machines, the high failure rate items sell very fast (and at a premium).  This leaves the seller with the low demand items that they will often sell cheap just to get rid of them.

YMMV,

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I thought the same thing when I first noticed the part. It seemed like an awkward design to me.

However, both of my BM8000’s have this part in that location. I bought one of the BM8000’s used, so I can’t make any judgements about the originality. The other I purchased new and the only placed that serviced it was an authorized B&O dealer. It is possible that two different people did the same hack independently, but the odds are slim. Maybe it was a something from a B&O Service Bulletin?

Here is a picture of the button board from the other BM8000

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I’ve been able to do a full adjustment of the FM tuner on a BM6000. I more or less gave up on trying to follow the exact directions in the service manual since it was not clear to me how to translate things like the signal levels, etc. to the equipment that I have. Instead, I used the service manual as a guide, along with the schematics, theoretical descriptions of FM tuner operation, and (better) explanations from service manuals for other (non-B&O) equipment to interpret the “spirit of the adjustment”.

To relate the signal levels to my equipment, I made measurements of the other four Beomasters that I have that (I think) still had their original adjustments. I took notes and used the trends from the sample set to setup the tuner that I replaced the caps and trim pots on. This was a bit challenging since all four tuners were setup somewhat differently.

My newly adjusted tuner now sounds as good as the best of the other tuners and quite a bit better than the worst of the other tuners. I have no idea if it is actually adjusted “to specification”. It sounds “good enough” that any misadjustment isn’t readily noticeable.

I was able to do most of the adjustments with a digital oscilloscope, a multimeter, a TinySA, and a handful of attenuators. I needed one other piece of equipment to set the Channel Separation. The service manual called for a stereo encoder. I used a cheap FM transmitter, a waveform generator and attenuators to get the signal down to a proper level.

I’m happy with the results. I’m happier that I didn’t have to spend more than the receiver is worth on equipment to fix the receiver.

I still want to refine and improve my adjustment procedure. One of the things I still don’t understand is what they are trying to convey in this paragraph of the manual

What “signal” do they mean in the 2nd harmonic section and what is one supposed to adjust to get the correct waveform?

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