Refurbishing a Bang & Olufson Beomaster 3000-2

Discussion in 'Audio Visual' started by /invariance\, Jun 1, 2019.

  1. /invariance\

    /invariance\ Member

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    Quite a while ago I my father-in-law give me a B&O Beomaster 3000-2 as the tuner wasn't working, culprit was a broken component. I started off gallantly by getting a service manual to work out what the component was, sourcing a replacement, replacing the electrolytic capacitors and replacing the output transistors.
    Then life got in the road and it remained neglected under the house for some 10 years. :(

    Recently my in-laws (who I got this off) downsized and my father-in-law is getting frail so I thought it was about time to finish what I had started so he could come over with some lp's and play them on his old equipment.

    I'm regarding this as a refurbishment as I am tidying it up enough to look good, inhibit further corrosion and have running again. I would regard a restoration as performing a ground up rebuild with Nichicon (et al) caps, metal film resistors, full disassembly of the chassis for cleaning and washing the pcbs such that everything looks brand new, or even better.

    Here is the front and rear without the top or bottom affixed.
    IMG_1483.JPG IMG_1486.JPG
    I'm really mad at myself with the loss of part of the treble control. Whilst it was neglected all those years the aluminium top portion of the slider was lost, but by some miracle I still have the plastic front piece of it. Hopefully I will be able to fabricate something reasonable to repair that little problem.

    Overhead and underside views
    IMG_1484.JPG IMG_1485.JPG

    This is the broken component in the tuner, a variable capacitance diode
    IMG_1489.JPG

    Recently I started on the easier stuff - cleaning. The top was very dull and the sides had unglued.
    IMG_1488.JPG
    Glued back together and polished it up with Scandinavian Teak Oil. I was surprised that the timberwork is MDF with a veneer. For what B&O charges I was expecting solid timber.

    The bottom plate and rear grill are metal and were getting quite covered in spiders of rust. Stripped them back, undercoated, finished coat in mat black and to offer a bit of extra protection, gloss clear coat. Bottom plate:
    IMG_1487.JPG
    I left the decals alone, sanded and painted around them and clear coated over the lot to offer the decals some protections. (If it was a resto, it would incorporate remaking the decals).

    I luckily have some dial cord in my stash as that is broken on the unit along with a replaced capacitor(probably from 'storage' also). Waiting for some caps to come in on order to get that sorted.
     
    Last edited: Jun 22, 2019
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  2. OP
    OP
    /invariance\

    /invariance\ Member

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    The Front Panel

    Received the caps I needed and fitted them, now for a bit more cleaning.
    The front panel has quite a build-up of dust and body oils, so unscrewed the slide controls panel section, disassembled the slide controls, cleaned up the section with alcohol and applied Carnauba Wax to help preserve it. Interestingly it is a solid piece of aluminium.
    Yuk
    7587C7DA-75AD-481E-BD5D-B673C6988E1E.jpeg
    Hmm, this will be interesting
    2FE41AB0-FEBC-4696-9510-E37AF6165D68.jpeg
    This is the treble slide pot and is supposed to have two lugs.
     
    Last edited: Jun 9, 2019
  3. OP
    OP
    /invariance\

    /invariance\ Member

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    Been doing a bit more work.
    Removed the pushbutton switch assy off of the facia as the buttons (levers would probably be more accurate) were becoming quite tarnished and starting to corrode as well. I'm not sure if they were originally a matt finish as in just the natural aluminium with an oxide layer, or if they were polished.
    IMG_1505.JPG
    Removed the C-clip off one end of the shaft (actually not recessed for the c-clip) and went crazy on the cleaning - 400 grit paper, 00 grade steel wool and a rub over with wax. Sprayed some PTFE on the shaft for what it is worth.
    IMG_1504.JPG
    Here is the facia all cleaned up with the switch button assy re-attached and the slide control sub-panel cleaned up as well.
    IMG_1506.JPG
    Then moved onto the tuner dial mechanism. The bracket was corroding as well, so it got the treatment and then it took me days to eventually work out how the cord was looped around. Somewhat embarrassing, but I have never studied how they are set up before, so cut me some slack :lol:
    IMG_1507.JPG
    In the foreground of the above image is the bracket for the tuner preset dials, which are the grey edge dials to the right. The 'lever' buttons labelled 1 to 6 above are used in conjunction with these dials to "program" up to 6 radio stations.
    It is back together now but in the process one of the wires from the tuning pots that goes onto the adjacent pcb lifted the pad and broke the track. Bahumbug!

    Gave the internal side panels a quick sand and spray to make them look a bit better, too. Nothing fancy, just a bit tidier.
    IMG_1512.JPG
    Currently working on the FM front-end top and bottom caps as they are made out of tin-plate and they are both rusted.
    Quick plash of Rustoff and a few coats of grey paint will be adequate I think.
    IMG_1511.JPG

    Now on the search for a replacement for the damaged slide pot pictured in the last post.
    It is dual gang, linear, 20k ohm, 64mm slide with overall dimensions of 86mm L x 9mm H x 16mm D.
    IMG_1508.JPG
    If anyone has any ideas on a replacement or even how to repair the slider, please let me know.
     
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  4. Bold Eagle

    Bold Eagle Member

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    subbed - I hate throwing things away and think we need to repair far more often. Excellent effort so far and keen to watch the outcomes. Maybe even have a listen one day?
     
  5. OP
    OP
    /invariance\

    /invariance\ Member

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    Thanks Gumby and BEagle.
    Hope I can do it justice.
     
  6. OP
    OP
    /invariance\

    /invariance\ Member

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    What an ordeal re-assembling the front!
    Trying to fit and screw in the lamps, headphone socket and tuner preset pots to the fascia with limited space and connecting wire was a walk in the park compared to putting in three screws holding down the pushbutton switch assembly to the fascia. The red oval on the below image shows what was at hand. The top screw holds the switch button assembly onto the pushbutton bracket which is fitted pre-assembly. The pcb is for the switches and the bottom screw you see there is the little bastard. I would get one end of the switch assy in but for the life of me I couldn't get the other screw in, even with the screws loose.
    IMG_1521.JPG
    I eventually reversed my procedure and put this one in first and moved to the other end. Flat head, machine thread screws in a recessed fitting are shit!
    The red circle top right is the lifted pad for the tuner dial pot that had too much flexing :thumbdn:
    The main reason for the slow progress on this is I have been cleaning all of the screws (sand, steel wool then wax). Might be a bit over the top as they won't be seen from the front, but I want to stem any further corrosion and they would look pretty nasty against the nice shiny aluminium.
    IMG_1520.JPG
    After much elation I realised I forgot to test the indicator lamps before assembly. I really hope none are blown.
    Removed the screws from the transformer box to clean them up. Hope I never have to replace the tranny.
    IMG_1515.JPG
    Gave the outside of the box the same clean-up treatment and was about to work on the bracket holding the main filter caps, but it would have meant desoldering quite a few wires and being it is even less visible than what I have done to date, I thought 'stuff it'.
    I removed the mains switch mounting support as it has a bit of rust on it. Turned it over and 'hello'.
    IMG_1516.JPG
    I have sanded it down, painted it with Rustoff and sprayed it with grey primer.
    Onto the broken slide pot.
     
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  7. OP
    OP
    /invariance\

    /invariance\ Member

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    Ok, I couldn't help myself
    IMG_1524.JPG
    Ended up pulling out the bracket under the main power filter caps. Wasn't as bad as I thought to remove.
     
  8. Andres

    Andres Motor Admin

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    Enjoying watching this unfold. A very cool looking piece of technology.
     
  9. OP
    OP
    /invariance\

    /invariance\ Member

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    Thanks Andres

    A bit more action this week, Treated and painted the main power switch cover (centre), main filter caps bracket (left) and something that fell out when I was turning the amp upside down (right).
    IMG_1526.JPG
    Eventually worked out where it came from, it is soldered over part of the output transistor pcb.

    So, back to the slide pot. Looked around online and couldn't find anything I was happy with and there is very little in the way of B20K dual gang. If I did get something, there would be al lot of modification to the mounting and the slider.
    Here is the problem again, just a different camera angle
    IMG_1527.JPG

    Thinking through it I knew I couldn't glue anything on as there isn't enough surface area to adhere to.
    Then I had a revelation, a lightbulb moment! Melt a pin into it!
    An actual pin will be too hard to cut, so I found another use for the trusty old paper clip.
    IMG_1528.JPG

    Voila! Another exciting picture
    IMG_1529.JPG

    That is sorted and installed, so onto the cleaning up the control sliders and reassembling the 'control bar'. It's hard to tell from the overexposure from an iPhone flash, but the mouldings that are standing against the switches are quite yellowed plastic. I also have to source some 1mm aluminium to fabricate the top piece of the treble control.
    IMG_1530.JPG
     
  10. Bold Eagle

    Bold Eagle Member

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    It's good to see quality parts getting re-birthed.
     
  11. OP
    OP
    /invariance\

    /invariance\ Member

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    Awwwww Faaaaaaarrrrrrrrkkkk I can't get the dial cord over the little plastic pin on the back of the tuner slider and the cord fell off and damnit! :upset::mad::upset::mad:
    Eventually figured out how to prevent the dial cord from completely falling off the mechanism yet giving it enough slack to loop it around the tuner slider pin.
    IMG_1532.JPG
    Now to re-assemble the sliders and control bar (note this is my terminology, not B&O's if anyone goes searching). I suppose I should start using their terminology :rolleyes:
    The bar that the sliders go on is called the "Dial 87 - 104MHz", the plastic piece that fits into the slide pots are the "slide for pointer", the top and bottom aluminium pieces are the "screen for pointer" and the front clear plastic pieces with the red marker are the "Pointer glass". Personally I like mine better.

    I was thinking that to have the pointer sliders (is that any better? ¯\_(ツ)_/¯) already installed on the bar would make it hard to align with the pots so I put the slider rear pieces in place and put the dial bar on. Then went to put the top and bottom pieces on and found it couldn't be done that way as there are locking tabs to keep them in place.
    Looks like the only way is to assemble the sliders on the dial bar and then fit it to the fascia. But how am I going to get them to align with the pots?
    Fortunately it didn't take me as long to realise how to do it as it did with the dial cord. The pots are clipped on, just unclip them and pull out of the road, fit the dial bar, line up the sliders with the pots and put back into place. Simple yeah? Well, there is that bloody tuner slider to contend with, at least it won't be as hard now I figured out how to manage it.
    IMG_1534.JPG
    I have them now fitted, including the tuner slider, sans the pointer glass and top piece for two as I need one top to fabricate a replica.
    IMG_1535.JPG
    I really hope I don't need to take it apart to fit the last few pieces :Paranoid:
    I should start going through the circuit now and checking offsets etc. The tuner has me worried as I think I wasn't able to source an exact replacement for the varicap diodes which could make aligning it hard, especially as I don't have an am/fm function generator.
    Small steps. Cross that bridge.....
     
  12. OP
    OP
    /invariance\

    /invariance\ Member

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    Yesterday I had a look at the current adjustments. Read the service manual and had it powered up for a while.
    The manual depicts the AF pcb, some test points(?) to the right with the two lines running out of shot go to an ammeter.
    IMG_1539.JPG
    Ok, so where is that on the board?
    IMG_1540.JPG
    I see the trimpot, there is no overlay and what/where the hell is the test points suppose to be?????
    Fortunately someone else raised exactly the same question here and the response was the red/white and the red wires at the back right of the above image are the test points. They are push on connectors, simply remove and place the meter inline.
    The cable is coded red/white but the manual has it labelled r/hv, quick Google Translate to Danish is rød/hvid. Couldn't have been more obvious, right?
    Work got in the road of all the important things and had to leave it at that for the day.

    Powered it up this morning to warm up and stabilise whilst I had breakfast and when I got back, sniff sniff, oh that's not good.
    IMG_1541.JPG
    They are part of the protective circuitry for the output transistors (resistors 578 & 582)
    IMG_1542.JPG
    Great! more work :(
     

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