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Where did you get that lovely Beo Hub board from? I did have to replace a reed switch and a blown transistor on mine (TR6 I think?).
I have also had to replace the reed switch on a couple of these units, usually after i have invertedly grounded the 6vdc circuit…..its happened a couple of times when the carriage slide has moved too far in when i have been testing with the slider switches removed (schoolboy error)…..
You haven’t said if your measuring a voltage drop when the volume falls down….have you monitored this yet…i so is it falling off?
If you upgrade your membership to silver you will have access to the service manuals for mostly every B&O amplifier available…….
Firstly….is the existing fuse blown? no need to replace it if its good….I would buy a couple because often when you take these out the end cap becomes detatched and the fusewire pulls out of the glass holder, the fuse is 0.4A and sits in approx 14vac circuit.
The high temperature that has discoloured the yellow sleeve is heat generated from the voltage regulator circuit 2D4 (ZF6.8) 2R22 and 2TR6…..the fuse isn’t responsible for generating heat, this discolouration is very common as the regulator circuit does run hot…before you reconnect the fuse check you have the approx 14vac measured between the blue wire connected to the fuse and the blue wire connected to the PCB just above the rectifier…..this will confirm you transformer is giving the required voltage.
Craig
Made a mess of that…..the table shows the voltages that should be present at TP14 for mute on or off.
What do you measure on the input and output of the bridge rectifier 2D5 ? and have you checked the fuse hiding inside the yellow sleeve from the transformer to 2D5 ?
Craig
If your only input is currently the FM tuner your problem may be the muting circuit?
Craig
One way of determining if the 15v rail is falling off is to monitor the power ON lamp as this is fed from that supply.
Craig
And incidentally one way of testing the thermistor is to blow a hairdryer over it and the fault relay should activate and shut the amp down.
Craig
Bert
You dont say if the falling volume is occurring on all inputs i.e. FM tuner/phono/tape ?
Craig
19 October 2022 at 08:31 in reply to: Strategy for Changing Capacitors and Trim Pots on FM Tuner #39364Fascinating stuff……I have always thought it best to shy away from this subject due to the test equipment required and also the expertise required to perform it, but would love to learn more and explore the use of the TinySA piece of kit, I do have a BM4400 that has a less than perfect reception.
Craig
Couple of things here….firstly take out OTR4 and check it, if this is good you need to look at the power limiting part of the circuit….the set of contacts (those leaf spring contacts again) that need to be closed, thus shorting 7R1 to ground, when the solenoid is initially activated allowing max current to pull in the solenoid coil before opening up when the armature moves to drop the tone arm…..its possible you dont have a good connection at these contacts..
Craig
Yes…..Martin recommends doing this as the transistor does run quite hot, I did this on one of my units that I was having an issue with, didnt solve the problem as that turned out to be a contact issue as previously discussed
Martin recommends moving the voltage regulator 2TR6 from the 2 PCB and mounting it away due to heat issues…..I cant recall exactly but I have a feel ing the logic switches state around 0.5 to 2.5vdc and its the IC that supplies the power to “wet” the switch contacts I have a feeling that it all goes tits up if you dont have 4vdc min……
Well…..thats that little conundrum solved, shying away from what would be a difficult and expensive undertaking.
I’ve just had a look at the video on the b&o website…..and if i’m looking at the right one it yet again identifies the BG4002 or maybe BG2004 deck, none of the illustrations depict a BG4000 deck, is this because of the complexity involved……if one was to send them a BG4000 would a BG4002 be returned?…….I’m confused.com ;¬)
It may well be something entirely different, however it only takes one switch to be out of step to create havoc with the logic controls. I do suspect the old timer design engineers decided to create the most complicated deck ever built, integrating complicated logic gates simply because they could…..logic gates that are still in lots of modern day control systems (albeit in sotware format these days)…bear in mind the only thing that opens the switch is the quite light pressure of the leaf spring contact….take a look i nothing else other than to eliminate them from your enquiries
Alf
When you say you have cleaned the “those brass contacts” are you talking about the carriage transport switches?
I have had similar strange behaviour on a BG4000 deck that was eating my lunch for days….intermittent faults. Finally traced it to the transport switches (one in particular) and it turned out that the actuating plastic nipple that operated the brass leaf switch was sticking every so often….I had thought i would lubricate these switches with silicone grease to keep them moving freely…..mistake! cleaned all the lubrication off them and everything was fine…..just a thought.
There’s no question that it looks very attractive, and that its modelled on a 4002 unit. In my view it lacks the over engineered and massively complicated charm of a 4000 deck, the boolean logic controlling the 4000 is a work of art in itself…and the delicate reed relay stop start circuit is just so baffling that i suspect it must have been reverse engineered from an alien spacecraft dug up from the gobi dessert ;¬)
And does anyone know what the device is that Eric is injecting the circuit board with is, soldering flux perhaps. Looks like he is upgrading an existing deck from the oxidation on the internals, an old Elco Capacitor and the tone arm solenoid coil looks like it has warmed up the insulation over time…is image 2 the finished article Steve?
This could also be a noisy transistor……I have had this problem in the past.
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