ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
I probably paid slightly over the odds for this non runner but it's in nice cosmetic condition with rosewood veneer. It seems to be an earlyish version of this unit with only one idle current trimmer per channel in the output stage. No RCA sockets either.
It's clean internally too, though the switches needed a good blast of Kontakt 60.
The right hand channel was defective (practically no volume) and is now partly sorted, due in part to a defective TR40. But I still have a lot of hiss over the audio which I think is down to TR39, a lockfit BC159B.
My question is whether I can use BC559B as a substitute in this position? Lockfits don't seem to have the best reputation.
Also, there is some evidence of plasticiser migration as some of the internal wiring is sticky. I don't think the physical integrity of the wires is compromised. Is there any fix for this: such as cleaning with ipa or meths then some sort of clear coating?
Thanks all,
Simon
Yes, you can use BC559B - I suggest replacing in both channels.And there is only one idle current trimmer in each channel in all Beomaster 4000s.
Martin
The'4000 is( obviously )a development of the '3000,but with a different output stage,which employ's Darlington transistors,and sound's argueably better too?
You don't seem to have replaced all the caps on the output stage pcb(yet?)Those yellow jobbies need to come out,even if they read ok!And the presets of course.
You'll have the same problems with the function select switch,and you will have noticed that the radio section is the same as that used in the '3000.You have plenty of experience with that area of course!!!
Interestingly,the '4000 has an "ambio/surround sound function too,where if you connect an extra pair of speakers,you can achieve an ersatz surround effect,that's quite good.
A nice receiver,well worth some tlc!
Good luck with it Simon.
Nick
Thanks, Martin, BC559B nailed the problem.
I took out the bias setting Darlingtons TR43 and TR54 in order to remount them. They are SPS 5418.
I can't find a data sheet for them so I can't tell if they've gone low gain though they seem to test ok on my Peak tester.
Should I replace them with MPSA 13 as a matter of course (which show an hFE of approximately 10 times as much)?
Cheers,
Hi Nick,
Work in progress! Replacing trimmers/caps as we speak..
Don't worry too much about hfe for those transistors. Unless they are proven faulty, I would gladly leave them alone.High Hfe is not better than low. Particularly when we talk about amplifiers like this one.The risk of self-oscillation rises as you fit "to eager" components like higher-Hfe transistors and lower-ESR capacitors.Try aiming for something close to what's fitted originally.
And I agree on replacing the remaining capacitors on the board - the tantals too.- And replace tantals with tantals.Martin
Hi all,
Work progresses on the amplifier board but a couple of things have come up.
The service manual states that from set number 177100, the emitter resistors were changed to 0,33 ohm and the (external to the board) 8,2K/8,2K ohm voltage dividers have been changed to a lower value.
Well, my set is numbered 177418 and there is no evidence of any change. Curious.
I remounted the original TR43 and TR54 as per Martin's advice (fiddly job). The original TO-3 transistors on the back panel seem to have reasonably fresh (not dried out) thermal paste on them, so I left them alone. Heat transference from them into the back panel seems fine so I'm not overly concerned.
I needed to set the idle current so I thought I would measure the voltage drop over a single emitter resistor. The prescribed current is 80mA and the emitter resistor is 0,15 ohm. I should therefore measure 12mV across it.
I set the idle current to 12mv each side but was alarmed to see the output transistors get uncomfortably hot in a short period. I then reverted to the method advised in the manual and reset the idle current to 80mA, down from an indicated 100mA or so.
However, I now see only 9,5mV over the resistors but nothing is getting too hot. I probably need to whip them out and check they haven't drifted in value.
This got me thinking about the process of inserting a cheapish (or even not so cheap) Chinese DMM into the circuit - a Uni-t 61e in my case. Its shunt resistance is 10.4 ohms on the mA range which seems on the high side and must make a small difference to the measured value. Measuring an emitter resistor is clearly a tidier way of doing this if you know the exact value of the component.
Or maybe the way to go would be to place a precision 0,5 ohm resistor into the circuit and measure across that.
Anyway, it's ok for now but I will revisit in due course.
Onto the tants..
Regards,
Evening all, and a Happy New Year.
The Beomaster 4000 is coming along nicely - if rather slowly.
I've now replaced all electrolytic caps including tants (bar a couple in hard to reach places) and installed multi-turn trimmers on the amplifier board, and a number of failed transistors as described earlier. Tants for the most part were in spec, but were showing elevated ESR compared to replacements.
I remounted the power transistors with new mica/paste and have done quite a lot of reflowing.
On FM it sounds great over headphones.
But I am getting quite a lot of hum on Phono with an open input with the volume slider at 50%. (Just at the moment, I have nothing to plug into it). Tape 1 and 2 input exhibit no hum, just some background noise which is slightly worse on Tape 2.
Is this to be expected, and will it quieten down with what shielding is provided by the top and bottom covers when in place and a Beogram plugged in? Or should I be looking elsewhere, like signal ground connections?
The phono hum on an open input seems to have disappeared with the installation of the steel bottom plate which is a relief, but it did prompt me to remake all the ground connections on the pre-amp board.
So, onto the finishing off. I've now replaced every tant including the ones in the front end and detector modules and loudness board, the last of which was a bit of a faff.
The ambio/stereo switch contacts looked somewhat oxidised so I took ithe switch off and cleaned it up. Ideally I should have dismantled it to do the job thoroughly, but I 'll see how this goes. Will be quite interested to hear what ambiophony sounds like.
Having wrapped up this repair and recap, I now find that this excellent Beomaster is all but unusable on account of transformer hum/buzz. This was not so pronounced until I wound up the idle current to 80mA and put it to work.
The chances of finding a donor transformer are slim, so I am contemplating installing a toroidal transformer which will be made to suit.
I know that Rudy and Martin have both done this conversion and I have learned much from their comments. However, I am aiming to do this inexpensively (around GBP 50) and in a manner which is reversible and above all, safe.
My proposed specifications are as follows:
I will bypass the voltage selector box on the back and install an in-line 1.5AT fuse. I'm not sure whether this would survive the inrush current so it might have to be a higher rating. There are ways of limiting inrush current with thermistors or relays but they would add complexity and heat.
Having functionality for more than one input voltage would serve no purpose in this usage other than to make use of the existing fuse holders, so I propose a single primary.
I understand that radiated noise is an issue so the new transformer will have an EMI/RFI shield around it made of silicon steel.
I lack a 3D printer to make up a baseplate so I'll see what's possible with acrylic or aluminium sheet.
I'd be very grateful for your advice and comments.
It will be neat to keep the design as original as possible Simon,but you could use a separate small transformer to supply the tuner?
This could make the choice of main transformer easier,and you might be able to find an "off the shelf" device too,rather than having to have something custom wound,with attendant cost.
I have a BM4000 with a "singing"mains transformer too,so I'll be following your progress with interest.
hi Nick
I found this on ebay germany
https://www.ebay.de/itm/Bang-Olufsen-part-Beomaster-4400-mains-transformer-voltage-setting-switch/143125501341?hash=item2152f1d59d:g:RHwAAOSw2EJcYAVq:rk:1:pf:0
should be the same as in the BM 4000
wilfried
Thanks for the link sir,but the '4400 main transformer is quite different from the '4000,although it's tempting to purchase it for future use.
Hello Nick,
Thanks for the encouragement!
I'm now finding a manufacturer for the replacement and the names that keep coming up are Airlink, Canterbury Windings and Toroidy in Poland.
Their prices seem pretty reasonable as well.
The new toroid has arrived from Canterbury Windings in the UK. It is finished in black acetate tape and has a 105 degree thermal cutout and GOSS band. It's smaller than the old transformer box and over 1.2 kilograms lighter. I will make up a 1.5mm aluminium mounting plate that uses the old screw holes.
I opted for a single 230 volt primary winding. This means the voltage switch at the back will be redundant but I will keep it to avoid changing the look of the device.
The toroid is rated at 280VA and I am wondering whether a soft start circuit driven off a small auxiliary transformer might be desirable to limit inrush current.
Can anyone advise me how to remove the power cord grip (needs new cord) and the power switch? The switch has a metal shroud which comes off easily enough, and then a plastic shroud, but I am unclear how to remove that for fear of breaking something. The parts diagram is no help.
Any advice gratefully received.
Krolroger
The plasic cover just slides off the switch assembly, its not the best fit...in my limited experience....but a bit of a careful tug may be required. It's also fun getting it to sit correctly on replacement too.
Craig
Hi
In a final attempt to save the old transformer maybe you can try the following trick to reduce or even eliminate buzzing:
https://www.diyaudio.com/forums/power-supplies/326670-cure-buzzing-chokes-transformers.html
Milton
Craig, thanks for that. I think that removing the plastic shroud will likely sacrifice the switch, so for the time being I will leave it.
Milton, thanks. Unfortunately the original transformer is already potted within its box, so the addition of varnish is unlikely to help with loose laminations. The only possible solution might be to bake it at a lowish temperature but that may produce unwanted side effects.
Thanks for doing and sharing the groundwork that you have done with this project Simon.Presumeably,Canterbury Windings could produce more of these transformers to order as they will have the spec.on file now.I imagine that a similar but lower power version could be made up for the BM3000-2 now also?
The mains transformer and function select switches are the two "Achilles Heels"of these otherwise robust designs.
One thing's for sure and that is that you can't neatly change the smoothing and output caps on this unit unless you remove the mains cable. With a bit of controlled force the plastic shroud came off the switch and I was able to disconnect and tuck the cable out of the way. Nine or so ground connections to the negative of the smoothing cap (Vishay 256 series) required a bit of jiggery pokery and heat shrink.
Smaller dimensioned caps will give me the extra few millimeters I need for the toroid.
Fixman double sided tape is useful for securing caps in position.
This is the data sheet for the new transformer. Terry Monaghan at Canterbury Windings is very knowledgeable and answered my questions. He will design and construct to your specification. It took five weeks from order to delivery.
I paid GBP 101 including UK delivery.
Rudy (Beolover) says he paid USD 450 for a BM 4000 toroid in 2016 but that included two primary windings one of which had an additional tap as per the original specification which enabled use of the original voltage selector.
The metalwork is now finished and I have installed the new tray with the same clearance the old transformer had relative to the bottom pan. This will give adequate space for the lead outs from the toroid. With the new big caps installed and their retaining bracket flattened to the new narrower profile, I now have minimum 2mm clearance left to right, and considerably more front to back. The new transformer will be secured with a countersunk M6 bolt, and sits on a 3mm neoprene foam pad to minimise any mechanical noise. The left hand sidewall is also lined with neoprene.
I reused the old transformer support brackets after drilling out the spot welds, so that has saved a bit of labour.
I removed the old mains lead and have replaced it with 0.75mm 2 core flex with standardised colours. Getting it out was a bit of a faff, but using a razor saw as close to the back panel as possible and slicing through the retaining grommet did the job. I was able to reverse the grommet and reuse it. It needs to be temporarily compressed with thin wire to enable it to pass through the back panel.
Purists should read no further, but I can assure them that no irreversible changes have been made to this Beomaster and no holes drilled - apart from decommissioning the voltage selector.
I had a number of concerns about the old mains switch and decided to use a power relay to switch the 275VA load of the transformer and 5000uF smoothing cap. I am using an DPDT Omron MY2 relay with a 240VAC coil. It has a 10A current capacity and can switch an inductive load of 2A. It can be easily inspected and replaced in a matter of minutes if required as connections will be made with faston type connectors. It is mounted on the internal rear wall of the unit on an thermally coupled aluminium plate that will carry the new rectifier. This means the old switch will only be handling the (inductive) load of maybe 10mA drawn by the relay coil. I am hoping a snubber won't be necessary.
No idea as yet whether a 240VAC relay coil is going to introduce any noise but it's as far away from signal inputs as practicable. It may be necessary to shield it.
This is an experimental project though I hope for a decent outcome. If anyone has any suggestions that will improve my chances of success, please post them. In particular, I am wondering about screening and shielding of any mains borne noise, and fusing arrangements. I plan to use a 1,6 AT fuse for the transformer and 40mA F for the relay coil, using the two fuse holders on the back.
The relay, fuse board and transformer primary side are now secured in place and connected (temporarily in the case of the new toroid). There is no mechanical noise at all, even on switch on. The relay switches quietly and there is no evidence of arcing on switch off - though it will not be under load until I connect up the secondary side.
The voltages on the secondary side are 53 VAC and 24 VAC which will come down under load. The toroid is rated at 230 VAC. Were I to do this again, I would specify a 240 VAC primary.
I rewired the fuse box to retain use of the two holders. One fuse is rated at 50 mA and protects the relay coil (current draw of 4.9 mA) and switch wiring, and the other is a 1.6 AT rated fuse for the transformer. I have installed a standby led on the top of the fuse box which is connected to the changeover contacts on the relay. It is a reminder that while the unit is plugged in, the fusebox is live. The pilot light extinguishes on switch on.
And the fuse box. The control side wiring is 22 awg silicone sleeved.
This modification seems to work well. There is zero mechanical noise from the toroid and no induced hum in the audio signal. The relay arcs slightly on make but I can't see anything on break.
The photo shows a bit of a lash up with the wiring as I was anticipating having to rotate the toroid to minimise any induced noise but this has not proved necessary.
It remains to tidy the transformer connections and wire in the 105 degree thermal cutout. I will use appropriate crimped and faston connectors which will enable easy removal of the transformer and relay. I will check rail voltages - not that there is much I can do to change them - and the idle current.
I have fitted a heatsinked Vishay GBU 8A bridge rectifier in place of the previous B80 C5000 lump. This is much smaller and can withstand higher surge currents - which is probably just as well as I think the new transformer is slightly overspecified. (The main smoothing cap of 5000uF would suggest a smaller current requirement than the 5.85A rms my unit is capable of delivering)??
Good Job and solution I like it
Collecting Vintage B&O is not a hobby, its a lifestyle.
Yes, I am with Søren. Very nice work. Thanks for documenting the restoration with photos as well as description.
-sonavor
A very nice job sir,and thanks again for sharing the details too.
It's not only restored another beauty to full operation,but must have improved the spec too?
I'm not sure about the blue power light btw,praps it's just me?
Gentlemen, thank you for your kind words which I greatly value.
Nick the standby light is red, not overly bright and hidden from direct view by the metal grille at the back. I did think instead about running 1.5mm fibre optic cable to a new hole in the front panel but decided that would ruin the aesthetic.
Anyway, I guess this job is absolutely do-able with a good quality toroid and some patience and some aluminium sheet.
Will post again when I have wrapped it up.
I thought that that device was perhaps a resetable cut-out Simon,after your earlier concerns about surges?
The blue light I meant is the power "on" lamp at the front of the unit.It seems that the tuning lights are blue also?Have you used led's here?
No led replacements - in accordance with the Dillen Doctrine. Might be your screen playing up.
Best,
On my monitor the lights on the front of Simon's Beomaster are a green lamp and three red lamps.
Prap's I should have gone to Spec****r's?
solderon29: Prap's I should have gone to Spec****r's? Nick
I didnt want to say that
I've now finished this project and here are some final pics.
I found crimped closed end connectors useful for wiring in the transformer connections. This enabled the wires neatly to double back on themselves rather than round in loops.
There is a small amount of capacitative coupling into the metalwork of the Beomaster. As the plug is polarised, I will live with it.
Note the faked up voltage selector (doesn't rotate). The fuse ratings are stated inside the fusebox door.
I removed the old finish with acetone. After several coats of Danish Oil later, the rosewood has come up nicely.
One day, I'll get a rabbit's ear aerial with two unbroken dipoles...
Oh! that's a transformer!
You had it manufactured to spec ?
A very impressive job sir! It just needs one of Martins preset cover's now,and I'm relieved to see that the indicator lamps are the correct colour in this piccie too!!!(beam me up Scotty?)
And your next project is?