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For those having similar issues:
My unit has the earlier PCB2 design (serial 2887011).
I highly recommend replacing most if not all electrolytic caps, especially with the BC9000 and its complicated circuitry.
In my case, 2C108 (right) and 2C208 (left) were about 50% out of spec. These have something to do with how the Dolby chips switch between record and playback.
Replacing these immediately restored output signal on pin 14 on the Dolby chips.My B&O Icons:
Cant speak to the motherboard or storage, but updated display is from serial no. 23435307 onward.
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Some speculation here as I am not an electronics engineer:
I figured it was some kind of grounding issue. 5C110 takes the transmitters directly to ground – the original was a 10uf cap that was blown in my case. I tried some iteratively larger caps and found that the buzzing was getting quieter above 100uf. I stopped at 470 which does not completely eliminate the noise but you don’t notice unless your ear is to the speaker. I am not sure if this will have any ill effects in the long term but I have not seen any change in operation since swapping for a larger cap. I assume something like 1000uf might completely eliminate the noise, but again I am not sure if this change will affect any other function.
Works for now!
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Popped the shield off of PCB4 to discover that the actual software on the chip is 2.2. Must have been updated at some point. Regardless, no change using different connections and inputs. Still buzzing. Haven’t found any faulty components or incorrect voltages around the transmit circuit.
Electrically, what could be causing the noise? Something spiking the voltage when the emitter diodes are flashed? Grounding issue somewhere? When I received it, there was a bad rectifier diode (D19 – IN4002) and a blown fuse. Could this be related?
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The official answer from B&O is to disable L/R speakers in the Theatre. You’ll get muddy separation otherwise.
However, play with it both ways and see how it sounds. Nothing stopping you from experimenting.
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Alternatively, is there a way to disable 2-way communication? I’d like to use the BL7000 for control but don’t necessarily need the feedback from the BM4500. This would eliminate the noise as it only happens when transmitting.
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Interesting. I’m using a Beosound Core for testing (RJ45-DIN) I’ll try some different sources and connection types.
I found the same thing online, yet this one definitely states 1.6 on the back sticker, and has both IR receiver and transmitter on PCB5. It does not have the extra IR that shines through the glass panel like later versions did.
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I have also confirmed with my phone cameras that the noise occurs every time the 4 IR transmitter LEDs flash. The noise does not change with the speaker volume – always the same, even at zero.
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I have since come to a better understanding of how the “Auto” function works. There are two buttons on the bottom disguised as feet. When you set the unit down, the button contact closes and the unit goes in the the “raised” position. When you lift the unit the contact opens, setting it to the “down” state. It is no more complicated than: Closed=Raised, Open=Down.
In my case my battery cover was bulging due to temporary wiring, so the button could only close briefly when setting it down. A temporary lift due to temporary button press. Problem solved!
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No luck so far, my working one reads 17v momentarily when arm is manually lifted at 1R64 (as per service manual), but the not working unit does not receive this pulse. Still playing with it but any input would be great!
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That makes sense!
Of course one more problem found – the up/down button will lower the tonearm, but will not raise it. Pressing any of the other buttons will raise it if it is down, but not the up/down button. Back to the schematics
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Found the culprit – a bad 1D16 diode. Both the detector arm and solenoid are now functioning correctly. Would you mind telling me how this diode affects both circuits?
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One area i have noticed a difference between the two is working my way back from the detector arm. 1R36 should have 21v on the high end and 9v on the low end. This is true for the working 4004, but on the 4002 I’m getting 21 on the high and 20 on the low. I checked TR5 and it seems to be good.
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I have replaced the caps, sorry for not mentioning. No difference after replacing.
On R42 I am getting 18.57v on one end, and 18.31v on the other. On Tr11 C I am only getting 0.643v dc.
I have a working BG4004 to test against and the readings for R42 and TR11 are very similar.
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Considered getting new motor, just don’t want to have the same issue if I do!
I’ll check on that resistor too, thanks!Martin, the capstan belt is correctly seated around the larger section, and the smaller belt is down at the bottom section, not wrapped around but pulled to one side.
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One other thing – when I first plug it in, the platter spins backwards for about 3 seconds before stopping. Happens every time I plug it in.
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Apologies, I am currently using a BeoAmp 2 for testing and PL connection, not BL passive.
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I’ll have to experiment more. It seems like any time I press 9 while in shift mode, it immediately leaves shift mode. Does SHIFT have to display on the screen throughout the full 90258 code?
And of course since SHIFT+9 is a CD code, it brings it out of standby every time.
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Thanks for quick reply!
I have a good amount a tech expertise, and am comfortable replacing parts and capacitors. In this case I’ve already replaced the tape belt in this unit.
First thing I tried was cleaning the lens with isopropyl alcohol which didn’t seem to make any difference.
I’ll have to run through the test modes later today.
I’ll also look into which capacitors I need to replace first for laser.
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