Recent repairs

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Beobuddy replied on Sun, Feb 16 2014 3:50 PM

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Dillen:

Took out the datalink pins from the DIN on the captured signal cable and plug'ed it into my B&O TG7 signalgenerator.

I've modified mine with a 7 pins Din version. So you don't have to remove the pins (which sometimes fall down on the ground..).

I used the Left and Right switch above the Din-connector to power on or off when used with powerlink speakers. (I don't think a few volts will damage the audio from a occasionally connected taperecorder. 

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Dillen replied on Sun, Feb 16 2014 4:05 PM

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That's a possible workaround if you feel it annoying.
I must admit to be using the left & right switches far more than I remove datalink pins, though.

Martin

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Beobuddy replied on Sun, Feb 16 2014 5:30 PM

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I have to correct myself. I've used 8pins DIN instead of 7 DIN.

This way I can use standard powerlinkcables for testing purposes with active speakers or amplifiers (like eg. Penta's).

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Dillen replied on Tue, Apr 8 2014 8:19 PM

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Beogram 4002.
Arrived from the beautiful mountains of southern Germany.
The owner told me that the Beogram no longer behaved correctly and he was quite persistent, telling
me three or four times that nothing had been spilled into the Beogram so, naturally, I was quite
curious to open it when it arrived...
And, what do you know - huge surprise - something had been spilled down between the platter and the
surrounding aluminium, just to the left of the operating panel = right down onto the main circuit board.
The upwards facing solder side of the board had corroded quite badly and some kind
of white powdery deposit had build up from the acid eating away the boards copper tracks.

Why not just tell it like it is ...
Well, anyway, the main board had to come out and I spent a little time
checking that this was in fact the only thing that had been hit. And it was.
The board was cleaned off the heavy oxidation from the acid attack, a thing that contact cleaning
agent, being an oxidation shifter, is actually very good for, and it was apparent that four of five
copper tracks were so affected by the acid that major parts of the copper had gone, letting the
board base material shine through.
In cases like this I like to dig around a bit in the dungeons and find a good replacement board but
I couldn't find one of this particular version so a couple of thin leads were fitted, bridging the
broken tracks. A replacement board would have made for a cleaner repair but this was, if nothing
else, a decent repair using what was already present so not very far from my usual methods and it
turned out quite alright.

The 33 RPM speed dial light was out. A fresh lamp sorted this.
The usual dry spots in the mechanics were attended and a drop or two of sinter oil was added to
the bronze main bearing for good measure.
As is quite often seen, the stationary rear hinge block which is cast from some form of metal, had
shed the majority of its black paint - it flakes off - and in agreement with the owner, I took the lid
apart, sanded and re-finished it. For a deck that is otherwise near mint, this made it much neater.
After a good soak testing back it went.

Martin

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Dillen replied on Tue, Apr 8 2014 8:25 PM

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Beomaster 4400.
Handcarried by a Copenhagen based owner.
This one "made a funny hissing and pop noise". It played on but the owner got worried and
wanted me to have a look at it.
Apparently, it had some new capacitors fitted fairly recently, a couple of cheap chinese ones were
found, of which some were not even perfectly round but some high quality caps were also
found here and there.
A 100uF capacitor in the right channel output stage, one of the better quality components used, was
not exactly a happy camper. It had been fitted the wrong way around and with its polarity reversed
it had pulled the emergency brake and the upper end had domed outwards enough to actually split
open its housing.
A handful of new caps replaced the defective one plus some of the cheapest looking types found elsewhere.
No other problems were noted.

Martin

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Dillen replied on Sat, May 10 2014 9:29 AM

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Beomaster 4400
They seem to come in waves. This is the fourth Beomaster 4400 in a month or so.
This one blew the left output stage and the owner brought it to "someone who could fix it".
Things didn't work out too well and when the owner got it back it was completely silent and could
do nothing but light its overload lamp.
I have a weak spot for cases like this and the Beomaster 4400 is always a joy to work on so I accepted to
take a look at it;
The left channel was the one that intially blew but I could tell that, at the time of arrival here, both channels were at fault.
With the cover off, I could tell that both the left and the right channel output transistors had been "tampered with".
Cooling paste fingerprints, lose nuts and soldering that looked far from original.
I came to the conclusion that the previous repairer took out the blown output stage transistors from the left channel
and, presumably due to lack of correct transistors, took the ones from the right channel and transferred to the left.
He may - or may not have realized it, but the transistors blew again immediately.
He then fitted some new transistors in the right channel. Unfortunately, they were two original looking and
two dodgy looking, probably counterfeit, and furthermore he managed to get the leads to one of them mirrored.
They blew too!
Now, sitting there with two blown output stages, he must have realized that things didn't quite go the right way and
he gave up on the thing.
On the bench a brief test with a multimeter suggested the replacement of a diode in the left channel. I then fitted four
new output stage transistors, replaced the idle current trimmer (as I almost always do) and I had that channel up and
running.
The diode in question is of course visibly present in the unit but for some reason it has not been documented in
the schematics so that may have fooled the repairer. I can't say.
The right channel also received four new output stage transistors and a new idle current trimmer but, brought up slowly
on a B&O SN16A power supply with current protection, it was clear that something was still amiss. Even after spending more than
an hour with the schematics, I couldn't point my finger to any single component(s) able to cause the peculiar
DC offset behaviour that this channel experienced.
And actually, I was right. There were no defective components in that channel but the previous repairer inadvertenty
bent one of the vertically mounted resistors enough to allow its exposed pin to touch another nearby component in a
completely different part of the amplifier circuit.
I carefully bent the components back, away from eachother, powered up slowly again and that channel was running too.

More and more people show interest in the Beomaster 4400 and for good reasons.
It's a wonderful amplifier (and brilliant tuner too!) and its design is unique.
Many teenagers never heard what music can sound like, they have only ever heard MP3 and I-whatever sound, maybe
even played back on their cell phones and they are immensely impressed and blown away when presented
with the sound quality of a decent system of the late 1970s and early 1980s.
They seem to ask themselves why on earth we now accept much less.

Martin

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Piaf replied on Sun, May 11 2014 2:45 AM

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Hi Martin,

I must say how much I admire your dedication and admiration for all things Bang & Olufsen. I especially respect your affection for the Beomaster 4400…. You describe it as if it were a technological work of art. And maybe it is.

However what really sets you apart is your interest in both the consumer as well as their B&O gear in need of a good dose of knowledge and TLC. (A wonderful combination)

I salute you for all your amazing work!

Jeff

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Barry Santini replied on Sun, May 11 2014 3:11 AM

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Piaf:

Hi Martin,

I must say how much I admire your dedication and admiration for all things Bang & Olufsen. I especially respect your affection for the Beomaster 4400…. You describe it as if it were a technological work of art. And maybe it is.

However what really sets you apart is your interest in both the consumer as well as their B&O gear in need of a good dose of knowledge and TLC. (A wonderful combination)

I salute you for all your amazing work!

Jeff

Beogram 4000, 4002, 4004, 8000, 8002, 1602. Beogram 4500, CDX. Beocord 8004, 9000. Beomaster 1000, 2400, 4400, 4500. BeoCenter 9000. BeoSound Century. S-45, S-75 X2, MC 120.2.

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valve1 replied on Sun, May 11 2014 6:04 AM

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Great work Martin, all 4400s are worth saving.

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Dillen replied on Fri, May 16 2014 8:06 AM

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Beocord 2400
The cassette version in oak finish.
Owner complained that, after something had been spilled onto it, it would no longer record.
The VU meters would react and everything seemed fine but nothing ever reached the tape.
It did, however, erase fine so something was working.
A long row of switches is activated by the record button and oxidation to these switches is often
the cause of record malfunction but not this time.
Clearly, the spillage had something to do with it so attention was first directed towards the area around
the cassette door, around which the fluid had apparently entered the Beocords inner quarters.
Looking around a bit, it was soon discovered that the record/playback relay, sitting on the main board right
under the left edge of the cassette door, had been soaked in the stuff. The relay was powered but no longer clicked
when activating the record button and it looked all corroded inside.
I replaced it and the fault cleared.
The circuit board was also cleaned a bit but the relay seemed to have taken pretty much all that came down from above.

Whatever was spilled on it had attacked the eloxated aluminium top surfaces of the Beocord so drastically that
replacement surface panels were the only way forward. The owner already realised this so he had purchased
a Beocord 1900, which is a very similar looking unit, only with electronic differences, to
donor its nice panels and brought it in together with the Beocord 2400.
The donor also had a nice rosewood trim and the owner wanted me to transfer this to the Beocord 2400 that was
in oak, showing more than its fair share of chips. Not only would this make it nicer to look at, it would also match the
rest of his nice vintage setup.

They are nice decks, these Beocords. I remember using two Beocord 1900s for many years during the early 1980s.
I still have the tapes and I gladly listen to them.
Technically not a particularly advanced deck but a good and solid build, incredibly stabile and electronic faults are rare.
They were popular models, particularly the Beocord 1900 and there are more decks still in use than you may think and
owners tend to hold on to them.
Worth adding one if you already have a Beomaster 1900 or 2400-based system.

Let me take this opportunity to inform owners of Beocord 1900 that their deck is not at fault because the VU-meters don't
react during playback. It's like this from the factory. They only react during recording.
Same goes for the Beocord 1500 (baby brother to Beocord 1900) whereas the VU-meters are in action both during
recording and playing on the Beocord 2400 (biggest brother of the three).

Martin

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Rich replied on Fri, May 16 2014 3:32 PM

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Dillen:

Worth adding one if you already have a Beomaster 1900 or 2400-based system.

 

I couldn't agree more, and not just to "complete the set."  I have both systems (each with a BG3404) and listen to prerecorded cassettes on occasion.  These decks/systems can give excellent playback performance with good source material.

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Dillen replied on Sun, Jul 20 2014 8:11 PM

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DUX portable record player.

I rarely do anything outside the B&O audio range but every once in a while I get excited and curious and not too
hard to persuade into looking at other things.
This little classy piece of history was brought to me completely in mint condition but unfortunately only producing sound
from one of its stereo channels. The other channel was dead silent.
I first swapped the speakers and could immediately rule out both, they were absolutely  fine so the problem
had to be inside this very easy-to-service unit.
The amplifier is based on the SBF 3B driver IC, a long obsolete type that has no modern equivalents.
Obsolete ICs may not be impossible to find but typically difficult and often very expensive.
The driver IC feeds the simple push-pull output stages, consisting of one AC187/AC188 germanium pair per channel.
This setup was heavily used in the many similar Philips decks from this period and DUX was also a
Philips subbrand so not a surprise.
One output was correct at about 50% of the 14V DC supply measured before the output series capacitor, the
other was close to zero so obviously wrong.
Lifting a few transistor pins away from the circuit allowed me to identify the problem components as being the
output stage transistors with the output from the IC still alive and kicking, phew...
So far so good. I dug around in the drawer and found a good used AC187 harvested from some
scrapped donor decades ago and, lacking an AC188, I found an AC139 that was similar enough to do the job.
Afterall this is nowhere near an audiophile unit and distortion is not something you'd like to measure, even on a
factory new unit, so they were soldered in and away it went.
Nice stereo sound - err... well - at least stereo sound, but that's all this little unit promise so fine with me.

Note: Desoldering one of the leads to the platter motor will allow you to power up the amplifier for diagnosing
and measuring without having to switch on/off the deck all the time.

Martin

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andre replied on Fri, Jul 25 2014 8:43 PM

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Hi Martin

My compliments for the best read of the year in this thread. It's very cold and rainy here in Cape Town but your repairs and fine writing style made me forget about the bad weather outside. In fact, reading this, it (almost) forget my troubles with my second 4002/6611.

All the best  and thank you for your kind reply in another thread.

dauphine/andre

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Dillen replied on Sun, Jul 27 2014 4:16 PM

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Thanks for the feedback.

Martin

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Dillen replied on Sun, Jul 27 2014 4:16 PM

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Beomaster 3000

This one arrived with a note on it stating that it was shutting down
intermittently and very sensitive to using and touching.
After travelling with the post, it was now completely dead.
That's not as bad as it may sound because intermittent faults can often be
a headache to find. Intermittent faults will, for some reason, often not show
up on the repairbench, only when back with the owner.
Solving faults that come and go is often helped in no minor way by a mix of experience and
educated guessing.
And how can you tell if you have repaired the intermittent fault ?
Permanent faults are much easier to deal with. Not necessarily easier to repair but
usually easier to locate.

So this one should be fairly easy. No power anywhere. I remember that the
power switch in some production batches had some problems so it was my first suspect.
Easy diagnose, switch on, check for power before the switch and check for
power after the switch.
I had no power anywhere so the switch was not the cause.
The voltage setting switch then? If not used (like most) it can develop oxidation
and bad contacts. I unplugged the Beomaster from my variac and rotated the switch
back and forth a couple of times.
(Always unplug from mains when rotating the switch!).
That didn't help.
The fuses then?
Bingo! Both fuses looked dodgy, and when I say dodgy I really mean dodgy.
Apparently both had blown at some point and instead of replacing them with fresh fuses
of the same type and rating, their glass envelopes were opened and a small steel spring
fitted inside each of them.
The steel gave no good contact and the arcing that had taken place inside the glass
tube did not improve matters.
When taken out of their holders the fuses practically exploded from the internal spring pressure.
Two new fuses cured the thing completely.
The idle current trimmers and a few others were of the good old bad type so was
replaced and adjusted.
A fresh set of lamps, eight hours worth of playing and out it went.

Martin

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Dillen replied on Sun, Jul 27 2014 4:39 PM

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Beomaster 901
This one arrived from Sweden. Great feeling to look at a practically mint one like
this, how nice to know that there are still people out there, caring for their property.

Sizzling sound, it said on the note.
I plugged it in and brought it up slowly on my variac.
Sure enough, it was sizzling.
But not from the speakers, - from the Beomaster itself! Power off now!
Covers off. Look inside.
It took me about four seconds to spot a small stream of liquid running from the
ventilation point of one of the large output series capacitors.
Problems like this can give a terrific experience. I wouldn't like being in the
same room should one of these buggers suddenly decide to quit the job with a bang.
And they are known to do just that!
This one was nice, giving us a short notice.

The leaking cap and its brother in the other channel were replaced after which
the radio played along happily without sizzling.
The usual good handful of caps and trimmers were replaced as well to give the
little thing a good help into the future.

What nice radios they are, these Beomaster 901s.
Lovely design, definitely not the worst construction and a wonderful warm sound.
No wonder they were so popular.
If you never heard one, you really should treat yourself.
Pair one up with a nice set of Beovox 1100 and you'll have a fantastic sounding setup.
Actually you cannot fit too large speakers to a Beomaster 901 so Beovox S45 or even S80
would be great. Let your room decide.

Martin

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Dillen replied on Mon, Aug 18 2014 5:09 PM

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Beocenter 7700
Handcarried to me for repairs.
Its owner told me that it hadn't been used for a couple of years but now that he wanted to
use it again it would no longer do its job right.
It would give nothing but a sizzling sound from the speakers and it no longer reacted
to commands from the panel.
I noticed the brightness of the red displays wasn't homogene and steady, instead it
was "waving", making me think that this could be the result of interference between the
display scan frequency and a ripple in the power supply to the displays.
The scope confirmed my theory; A nice 4V 100Hz ripple on the 6,5V supply. Not good.
This could only come from one place, namely the large C4 filter capacitor.
I took it out and measured it. No capacitance, no connection, nothing whatsoever inside
this nice and shiny aluminium can anylonger.
All three similar capacitors were replaced with shiny new blue replacements which
cured the faults completely.
According to my notes I replaced the tapedeck belts in this Beocenter about four years
ago and the tapedeck was still running fine so I merely gave it a quick cleaning before
phoning the owner to arrange pickup.

Martin

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Dillen replied on Mon, Aug 18 2014 5:14 PM

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Beocenter 7700
A lovely white design version.
Second 7700 on the bench today. This doesn't happen every day - not that I would mind if it did, really.
They are wonderful machines to work on.
The owner accidentally spilled "something" out over the panel under the large alulid. He cleaned off
as much as he could from the panel and buttons and the Beocenter worked for a couple of months but
then it would no longer stay powered on for more than a few seconds.
Sometimes the cause for a specific fault takes hours to locate so in cases like this, where
the most likely cause is already known, it's almost too easy.
Simply look around for traces of spilled "something".
In this case, the underside of the panel, that wasn't cleaned, gave away the exact position,
which was right over the right side amplifier section.
As it turned out, it was the idle current trimmer that took the drop. It was now in the form
of one large brown'ish pile of oxidation.
I poked it a bit with a small screwdriver and it responded by turning itself into brown dust.
I soldered out the remains of its pins, cleaned the board, looked around for other spots but
didn't find any, fitted a new trimmer, powered up and adjusted the new component. Checked its
brother in the other channel, decided to replace this cheap but quite essential component while
I had the thing apart.
Cleaned the underside of the panel that the owner couldn't access and introduced the piece
of thick tape over one of the tapedeck screws as mentioned in a tech note to avoid groundloop humming,
apparently it hadn't been fitted in this Beocenter so I decided now was a good time.
With no other problems in sight, I closed the unit, let it play for about half an hour while I cleaned
the workbench and called it a day.

I've often said it, but it strikes me everytime I have my hands into something non-B&O and
get a chance to compare; The vintage B&O items were expensive, yes, but it was quality builds
all the way (with only a few exceptions).
They are wonderful combo systems, these 7000-series Beocenters.
Impressive builds. Wonderfully designed and so incredibly well sounding, much better
than what you would normally expect from a stereo combination system but hey, it
doesn't say Philips or Goldstar on the badge either and the mere weight on
the thing suggests nothing but quality.
I still remember a DUX (Philips subbrand) radio, I once had;
I seem to remember it reaching no more than 2,5Kg on the scales. No wonder.
It was a very simple 2x10W stereo receiver, sounding somewhat alright driving
Beovox 2702s but flashing its dial light in perfect reverse with the music beat when
the volume was set at anything above a quiet whisper.
Poor design to the max.

Martin

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Dillen replied on Tue, Aug 19 2014 7:16 AM

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Beomaster 4400
This one came from southern Italy with a lovely handwritten note, telling me to "fix it up".
The owner felt that it no longer lived up to specs and he also complained that after a
local service it would now mute when AFC was depressed.
Understandably, he found that quite disturbing.
I've done about a handful of these wonderful receivers recently and they all needed a
fistful or three of fresh capacitors. This one was no exception but I wanted to fix the
AFC problem first;
It sounded to me like a problem related to the "Silent tuning" function. This function
provides the user with the pleasure of glorious silence when tuning between
strong FM stations.
This function is, of course, closely related to the AF/IF signal strength but also, in
a somewhat tricky and smart way to the two discriminator lamps.
- And the Beomaster came back with this fault after a recent service... hmm... Let me
have a look at those lamps!
Bingo! Wrong wattage lamps were fitted behind the two tuning discriminator arrows.
Actually I found two very different lamps in there, none of them correct.
With a set of correct lamps fitted, all functions were back.
I hope he got those lamps cheap...
The recap'ing was as trivial as ever. Not really boring, though. Just not full
of surprises and neither was the replacing of the idle current trimmers and the check
for cracked solder joints where the piggyback tuner boards are plugged in.
The 6 hour soak testing that followed was a much better treat. The Beomaster got the
opportunity to pull a pair of Beovox Pentas that I reburbished a couple of days ago.
I bet noone at B&O ever thought of this combination but it's not the worst, I can tell you.

Martin

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Dillen replied on Tue, Aug 19 2014 7:18 AM

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Beocord 7000
From Portugal.
The owner was rather desperate; The poor thing (the Beocord that is) had visited no less
than three different repairshops in his country, none of which managed to solve the problem.
One shop had it on the bench for more than two months (so they told him).
He asked me if he could send it to me.
I first told him that it would probably make better financial sense
to buy a working one and keep the other for parts or sell on as-is but after
all the trouble he had become quite stubborn, insisting to find someone who could repair it.
It HAD to be possible.
I admit to becoming quite stubborn myself in difficult cases and I could feel my
curiousity grow by the minute so I accepted it in for repairs.
It arrived, completely mint in its original box. Very nice.

Problem was that it would record one channel reasonably well but the other only very low.
I looked inside and put the scope to a couple of strategically chosen points in the
signal path. Programme signals (the familiar 1KHz sinus from my good old B&O TG7) looked
good all the way and so did the bias oscillator and mixing.
I ended up cleaning the tapeheads off an opague and particularly stubborn piece of gunk.
IPA did nothing so I put a fingernail to it and it sprung off and away.
Cleaned the rest of the tape path carefully and replaced the belts for good measure.
The owner was very happy to see it back in working order and he even sent me a holiday postcard.

Martin

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valve1 replied on Tue, Aug 19 2014 8:51 AM

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Great read Martin, glad to see you are keeping your international  presence.

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Rich replied on Tue, Aug 19 2014 12:52 PM

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Dillen:

I ended up cleaning the tapeheads off an opague and particularly stubborn piece of gunk.
IPA did nothing so I put a fingernail to it and it sprung off and away.

Now that's a photograph I would have liked to have seen!

Thanks for the continuing stories, Martin.  Of all the "stackable" Beocords, is there any one model that performed better than the others?  My BC4500 is a fantastic performer, but it's just not practical to place it (for example) in a cabinet.

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bidstonhall replied on Tue, Aug 19 2014 1:25 PM

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Problem was that it would record one channel reasonably well but the other only very low.

Sounds like a good description of my beocord 4500

must get in there properly to clean it, trouble is at my age my eyes are not that good and I can't see unless the light is good, but encouraged by martins find

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Dillen replied on Tue, Aug 19 2014 2:53 PM

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Rich:

[Of all the "stackable" Beocords, is there any one model that performed better than the others? 

In my opinion, the Beocord 5000 is the best performer of the stackable types.
Maybe because it isn't an autoreverse deck. It's stabile and reliable to a much higher level than any of the others.
It sounds a bit warmer too. Not so wearing on the ears.

Martin

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Rich replied on Tue, Aug 19 2014 10:56 PM

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Thanks.  Perhaps I'm just having deja vu, but I believe you have stated this opinion on the forum before.

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Dillen replied on Fri, Aug 22 2014 1:12 PM

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Beolab Penta
The owner brought one of his speakers to me for repairs. After a recent service it
sounded "dull and boring" as he put it and he wasn't keen on bringing it back in
for service under warranty the same place again so I agreed to take a look at it.
Dull and boring indeed.
In other words; Not a whisper of treble to be heard.
Off came the front grill and out came the center speaker baffle. Out came also the
multimeter and the DC resistance of the tweeter was checked. It was all fine.
What? Tweeters are quite sensitive parts and they are usually some of the first things
to burn if the speaker is overloaded etc.
Had to check the crossover filters then so off with the base that contains the amplifier
and take a look at the filter boards.
I could immediately see what the problem was and when I took out the boards, I could
also take a photo;

The "repair" guy apparently, got a screw fitted outside of its threading.
This screw munched its way, using the fiberboard for thread, pushing everything aside
as it went. Including capacitor C4, the tweeter series capacitor.
The capacitors pin was severed and I had to fit a replacement capacitor which brought
back the treble.
Clearly, this speaker hadn't been tested thoroughly after the previous service.

All the spade connectors were also soldered in this speaker.
I never got it; This type of connector is so strong, it can be difficult to pull
apart even if not soldered.
The same type of connector has been used in cars for decades, handling over 25 amps
with ease. We'll get nowhere near that in here.
And with the fairly short leads in the speaker tower and limited access it took me
about half an hour just to get the damaged board out. Then clean and solder back on...
Hysterical overkill if you ask me.

Martin

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Rich replied on Fri, Aug 22 2014 6:06 PM

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Dillen:

 

Clearly, this speaker hadn't been tested thoroughly after the previous service.

That's just unforgivable for a "professional."

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Piaf replied on Fri, Aug 22 2014 10:16 PM

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Very interesting thread indeed, I never cease to be amazed at Martin’s keen abilities.

However Rich you are been too kind, thoroughly tested? More like not tested at all. What kind of professional technician gives an item back without testing it?

From this description if the tech had just plugged in the speaker and turned an amp on he would have known something was very, very wrong.

Jeff

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cararescue replied on Thu, Sep 11 2014 12:34 AM

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Hi, sent you a pm but it came back! wondered if, within your 'dungeon' you may have a *** for a ***...the piece that ***.
Mine has broken at the bottom so the ***. If you do not have one....any advice on where I might obtain one please?

Read all your posts with great interest...sadly not covered the faults I seem to have on the ***! but will keep watching!

Edit by Dillen

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Dillen replied on Thu, Sep 11 2014 9:57 AM

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Hi,

I cannot tell you why PM doesn't work for you.
I get loads of PMs from others.
Try the email function - if that thing works.

A minimum membership level of silver is asked for to place sales/wanted ads so
I have edited your post accordingly.

Martin
(Beoworld moderator)

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Beobuddy replied on Thu, Sep 11 2014 7:34 PM

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Dillen:

This screw munched its way, using the fiberboard for thread, pushing everything aside
as it went. Including capacitor C4, the tweeter series capacitor.

This could be caused when owners/"repairguy's" remove the amplifier and then temporarily placed the bottom plate back with different screws.

Which obviously are to long.

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Dillen replied on Sat, Oct 11 2014 5:01 PM

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Beocord 2000 cassettedeck.
I've done quite a few of these Beocords lately. They are great performers, they are
beautifully designed and they are so easy to use.
Most are merely in need of new belts and perhaps a couple of capacitors but according
to my notes this Beocord had all that done about two years ago and it was still fine.
The owner told me that the sound quality had dropped considerably over a couple of hours,
now down to a mere mumble and it started after he cleaned the tapeheads.
I took a closer look at the heads and found that the tape mating surface of the
record/playback combo-head, that is usually a polished mirror-like shine, was now a
scarred and completely pitted structure with some small white deposits building up here and there.
The only solution to this was a replacement tapehead and a check of both the
mechanical and electrical alignments.
I asked the owner what on earth he had used but he wouldn't tell me, probably embarrassed,
so, unfortunately, I cannot advice against using whatever it was. Nasty stuff anyways.
For cleaning tapeheads, I always use IPA. It's available in small quantities as
bottles of "Tapehead cleaner" and one small bottle will last for decades.
You can use IPA to clean the whole tape path, the tapeheads, the capstan and
pressure roller and all tape guides etc. Use cotton buds and wipe dry.
Never use white spirit, acetone or the likes on tapeheads.

Martin

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chartz replied on Sat, Oct 11 2014 5:09 PM

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I'm pretty sure it was acetone... or some nail varnish remover from the missus

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Dillen replied on Sun, Jan 18 2015 7:20 PM

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Beogram 4000
This one had a most unusual fault in that it would play a record quite normally from
beginning to end, but if you lifted the tonearm using the lift or <</>> buttons while playing, it would
lift the tonearm as it is supposed to do but then it would lower it again immediately as soon as you
let go of the button.
In other words, where most decks usually fail in a way where the deck refuses to lower the tonearm, this
deck actually refused to pause.
The lift/lower circuit apparently worked fine so I checked the signals in the logic circuits and found
that 3IC7, which basically handles all lift/lower-control was the one that commanded the lowering as
soon as no buttons were pressed.
This IC was produced by Mullard and is one of the very earliest ICs used by B&O. They are quite reliable
components, I've replaced only very few of them over the decades and after checking this one thoroughly with
a scope it was also found to be just fine.
The problem turned out to be with the lowering buttons contact.
This is a break-contact (rather than a make). What this means is, that a poor contact, caused by
dirt, dust, oxidation or physical defects, is understood by the logic circuits as a button being constantly  pressed.
In this case the reason was oxidation - and lots of it. The contact consists of a round nail-head type point on
the board and a bronze leaf spring activated by the button by a pin going through the circuitboard.
Both were black from oxidation and so were a few other contacts on the panel so I took it all apart and
cleaned everything. This brought back normal functionality.

Looking at a unit like the Beogram 4000, it strikes most modern day repairers how complicated a build it is.
Today, all of its nice electronics would have been replaced by a single chip, probably just a blob of
black substance on a 1cm2 circuit board.
The controlpanel would have been a touch-display, back-lit in blue no doubt, and the
power consumption would only be a fragment of what it actually is.
But it just wouldn't be the same, would it.
The Beogram 4000 is an icon, not only by design but also by function and build. With all of its
quirks, temperamental issues and weak points.
It is not only an incredibly well-sounding record deck, it was a milestone and a winning product in
its own respect.
Besides, had it been a blob with a display, it wouldn't be possible to repair it.
Or worth it.
Or any fun.

Thank you, B&O.

Martin

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Dennis replied on Sun, Jan 18 2015 7:34 PM

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And thank you, Martin, for keeping these icons alive! 

/Dennis

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Piaf replied on Sun, Jan 18 2015 9:47 PM

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Martin, I second that “thank you” for keeping my OWN Beogram 4000 functioning.

Ever since Martin performed his “magic” on my ailing Beogram 4000, it has never given the slightest problem. (Well none worth mentioning.)

Temperamental, complicated, and fussy for sure, but as Martin says, so well worth it.

And to be perfectly fair I have many more problems with my Beogram 4002, although it has never seen a repair shop.

Jeff

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Dillen replied on Thu, Jan 29 2015 10:08 PM

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Beogram 8000.
I've done quite a few of these lovely decks recently. There seems to be a trend or at
least an abnormal rush on both vinyl records and the good old tangentials and both are indeed worth saving.
This one just wouldn't keep a steady speed. While no immediate problems were noted while playing
"everyday pop music", putting on a little violin music made it clear that something was indeed wrong.
Violin and piano music produce such nice sine waves and are so clear that they will almost always be
the first to reveal speed fluctuations. Wow magnifiers, so to speak.
First suspect in these decks is always the tachodics and most Beogram 8000 came with the good old bad
photographic type that will almost always need replacing but this one had a stainless steel type.
Very nice, but where did the wow then come from?
The scope told me that some of the supply voltages had a little noise, it looked a bit unusual,
- not a lot, just a tiny bit out of normal.
All capacitors had been replaced recently according to the owner, and the innards appeared accordingly.
One thing I noticed though, was that while the tachodisc was one of my own reproduction parts, the caps
were not from one of my kits. No axial type caps were fitted, instead radials were mounted with
their negative pin stretched out horizontally across the board to reach where the negative (far) end
of an axial type would have been.
This is usually an acceptable way to get around difficult-to-find axials and it was not a problem on
the main board but at the voltage regulators mounted on the floating chassis, there's
simply no room for solutions like this.
A thick radial capacitor will block the suspension, make the sound output from the deck sensitive to
touching the deck and it will also no longer be danceproof.
The repairguy apparently noticed this and the best solution he could come up with was to squeeze and
flatten the capacitor.
Simply press it to an oval shape, to allow for just a millimeter or two clearance.
While it did bring back normal functionality of the suspension - at least to some extent - the caps housing cracked
at both sides from this abuse. It may have worked initially but the fluids inside will have dried out quickly and
the capacitor was now acting like nothing more than two pins inside an empty aluminium shell.
No capacitance or connection left whatsoever.
A new capacitor - an axial type like the original - cured the wow problem completely.

Martin

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sonavor replied on Thu, Jan 29 2015 10:25 PM

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Wow!  The old hammering of a square peg into a round hole so to speak.  Those capacitors aren't expensive.  It is amazing the original repairer just didn't get the correct component in the first place.

Have you seen that type of repair before?

-sonavor

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Dillen replied on Thu, Jan 29 2015 10:33 PM

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I have seen lots of bodged things and self-invented repairmethods, but this one was new to me.

Martin

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Jeff replied on Thu, Jan 29 2015 11:22 PM

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Wow, reminds me of the old engineering term "Don't force it, get a bigger hammer!"