[hcraig244]

A very high percentage of problems experienced with these decks result from switches, either on the control panel or the transport slider. A switch out of position be it open or closed will play havoc with the boolean logic control gates, I have chased my tail for weeks trying to locate a problem that turned out to be nothing more than an intermittent sticking contact on a transport slider switch……an issue that had been identified as a possible cause by Dillen at the outset….however as it was intermittent when I tested the switch it worked fine…turned out that the silicone grease i had blobbed onto the plastic nipples (which I thought would help keep them free) was causing them to bind due to the viscosity……thorough cleaning and has worked fine since…….I’m rambling I know ;¬)

Craig

[hcraig244]

Ok…..start by checking the switch contacts on the carriage transfere mechanism, sounds like this unit has been stood idle for a while, they are a little awkward to get at but sounds to me they will need cleaning even if they are not responsible for your problem. Dont adjust any of the position screws.

Craig

 

[hcraig244]

Dont force it…..let it soak, WD40 isn’t popular on this site (I think the popular term for it is snake oil ) De Oxit is the cleaner of choice, however i would go for something like 3 in one penertrating oil…..leave it overnight.

Craig

[hcraig244]

Read/view this rom beolover

https://www.youtube.com/watch?v=IxIxHb8sZdg

[hcraig244]

[hcraig244]

Are both your tuning lamps working fine?

[hcraig244]

chartz wrote:

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)…..

[hcraig244]

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…….

[hcraig244]

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

[hcraig244]

Made a mess of that…..the table shows the voltages that should be present at TP14 for mute on or off.

[hcraig244]

https://beolover.blogspot.com/2015/05/beomaster-4400-phono-input-muted-and-AFC-not-working.html

[hcraig244]

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

[hcraig244]

If your only input is currently the FM tuner your problem may be the muting circuit?

Craig

[hcraig244]

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

[hcraig244]

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

[hcraig244]

Bert

You dont say if the falling volume is occurring on all inputs i.e. FM tuner/phono/tape ?

Craig

[hcraig244]

Fascinating 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

[hcraig244]

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

[hcraig244]

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

[hcraig244]

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……

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