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
The sort of good news is that the bottom half has survived along with the ground spring.....so just the top half required from Rudi
That is usually the case with the Beogram 4000 for some reason. Perhaps because it is older (I have had to repair a couple of cartridge connectors on Beogram 4002 turntables) but maybe B&O improved the connector later on. In all of the repairs of this type that I have done the bottom piece has been good while the upper part is the one cracked/broken.John
Jacques
Well.....after all this time we're back on the road, holidays and covid where the culprits, this turned up today!
Some tricky soldering to be performed...…..
I suspect I have pubic hairs thicker than these tonearm wires......total nightmare removing the insulation without removing any of the strands, resorted to melting the insulation with the soldering iron and teasing it away......everything tinned and ready for soldering.
Soldered up nicely..............
And, in accordance with accepted practice, a blob of "arleenes tacky glue" to help ease any stress on the solder joints during re assembly.
joined both halves together and put a blob of glue on the earth wire
Offered up the cartridge..........
It's a nice fit....sanded it a little to get a good fit in the tone arm
With the cartridge still in place fitted everything into the tone arm....had to do a little sanding to get a good fit, was very tight at first and I was afraid it may get stuck in the wrong position. When I was happy I applied some Aleenes Tacky Glue and pushed the whole thing home...
Did a quick check of the coils before the glue dries..........
Both channels look good......and I'm happy with the overall outcome so far, let the glue set and take stock of the remaining activites to close this one out
Soldering the connections on the underside of the PCB
Then the connections on the top....I had wanted to retain the grey earth wire as I was a little nervous of soldering so close to the very fine wires to the rear of the PCB....however the wire fell off during the process so I had to run the black wire direct to the earth connection after all....
Re assembly underway......
Test run with a BM5000 and a couple of speakers.......all sounds great, everything functioning as it should. However.......I have noticed that the transformer is running quite warm...one might even say hot. Not smoking or smelling of baking shallac or melting insulation, just hot to the touch, I'm not sure how warm these normally get after an hour or so play....i'm wondering if this has something to do with the low secondary voltage to the neon....could there be a short in the windings? it seems likely.....will it become an issue? I really dont know at this time....any words of wisdom would be welcome as always.....
Craig
Further to the above....I have powered up the unit without switching it on.....and the transformer starts to warm up far more than I like, so with the unit off and the transformer heating up I'm suspecting the rogue secondary winding previously feeding the neon lamp, my question to the forum is this.....if i disconnect the top 44.5 ohm winding from the circuit (this is not now in use for the neon lamp) will this adversely affect the remaining windings which will still be subject to 230vac without the additional 44.5ohm windings connected?
Craig: [...].if i disconnect the top 44.5 ohm winding from the circuit (this is not now in use for the neon lamp) will this adversely affect the remaining windings which will still be subject to 230vac without the additional 44.5ohm windings connected?
[...].if i disconnect the top 44.5 ohm winding from the circuit (this is not now in use for the neon lamp) will this adversely affect the remaining windings which will still be subject to 230vac without the additional 44.5ohm windings connected?
Oh yes it will!!Whatever you do, do NOT touch the primary windings!! They're fine the way they are.
Normally I wouldn't think that a partially shorted winding on the secondary side would be much of a problem, but depending on the way those wires are shorted there could be a small current flowing that causes the trafo to heat up unnecessarily.To confirm that the rogue winding is the problem, please do following:
Once we have those readings we can think about next steps.
Sound advice Manfy.....I have confirmed that the unused secondary wiring is indeed fully insulated from the outside world, at least the part of the wires not encapsulated in resin is.
First pic is across one of the fuses in the primary windings with the unit in Standby......
Second picture is measuring across the same fuse holder with the unit switched on........
The standby current looked high to me....so I measured from the same place in one of my fully functional decks....this is what i got
Same deck, same measuring point with the unit switched on......I will get to the secondary windings later in the day hopefully
Hi Craig, thanks! Yes, 71mA (or 18W) is definitely too high for standby. The 25mA or 6W look reasonable for a product from the seventies.
But without seeing the idle current on the primary winding when all loads on the secondary windings are disconnected we still do not know the source of the problem. Granted, the fact that the turntable seems to function normally suggests that the neon lamp winding is the culprit...but well, it's still just an assumption and not a known fact.To make it a fact you need to disconnect all secondary windings from the circuits and measure again. If you still read a high idle current, you know that the faulty neon lamp winding is to blame.
Well......got around to it this afternoon, disconnected the remaining two secondary windings and powered up the unit 56mA.............I think we have our culprit, the question is can anything be done about it?
Craig: Well......got around to it this afternoon, disconnected the remaining two secondary windings and powered up the unit 56mA.............I think we have our culprit, the question is can anything be done about it?
Yes, that leaves no doubt, I'm afraid.
Let's crunch some numbers:71mA - 56mA = 15mA -> That's the supply for the idle current on the 24V and 10V coils.The good unit draws 25mA in standby, ergo 25 - 15 = 10mA -> That's the magnetizing current in the primary coils.56 - 10 = 46mA -> that's what's dissipated in the rogue neon lamp coil (which acts as a heater now with 46mA * 240V = 11.04W).Previously you measured 165V instead of 220 on the neon coil and 900 Ohm instead of 1.3k, i.e. we do have a short within that winding and that thing burns 11W. Based on P=I^2*R and the 400 Ohm missing, we get I = sqrt(11/400) = 166mA and they are circling in that shorted sub-coil.
Hmmm, now that doesn't sound so good. Depending on wire gauge, this might be a real problem. If that trafo wire is SWG30 or bigger (=0.315mm diameter or smaller) this could cause more insulation meltdown potentially even affecting the 24V or 10V coils.
The best and safest option, of course, would be to replace the transformer...but if I remember correctly, you tried that before and it proved difficult...
Hmmm...if I were in your shoes, I'd probably test the transformer for a full day (outside the Beogram and in clear view, of course). I'd measure the trafo temperature with an IR thermometer, hourly or so, to see the max temperature it reaches and then I'd decide whether I could live with that. You said it gets "hot" and I assume that is around 60+ degrees Celsius. Even though that is uncomfortably warm it wouldn't be much of a technical or safety problem. If it gets anywhere near 80-90C, then forget it. It's definitely unsafe.
I would opt for spending the money to have a new, toroid transformer built to spec for the Beogram 4000.The only downside there in my opinion is the cost.Just my 2 cents but seeing how this is a classic, much sought after turntable (by B&O collectors), it would definitely be worth the cost to get it back into full operation again. With the restoration work Craig has already done so far this Beogram 4000 would be ready for another fifty years of enjoyment.-sonavor
Thanks for the support chaps.....
I don't have a IR thermometer, but I know that if something is too hot to touch its generally accepted as above 60 degC. In my view leaving this unfinished isn't an option....however the final say has to be with Justin. He will have to justify further outlay for a replacement transformer, providing one can be sourced of course.............anyone out there got a transformer they don't have a need for
sonavor: I would opt for spending the money to have a new, toroid transformer built to spec for the Beogram 4000.The only downside there in my opinion is the cost.Just my 2 cents but seeing how this is a classic, much sought after turntable (by B&O collectors), it would definitely be worth the cost to get it back into full operation again. With the restoration work Craig has already done so far this Beogram 4000 would be ready for another fifty years of enjoyment.-sonavor
sonavor
Had a quick chat with Justin this morning and we are in agreement that a replacement transformer is the way forward, we have searched in vain for a replacement and now think a custom built toroidal transformer may be our best bet...as you have already been down this road could you provide contact details and a specification for the unit you had built for your unit?, of course we would be looking for a 240vac primary winding version....
Regards Craig
Craig: [...] In my view leaving this unfinished isn't an option....
[...] In my view leaving this unfinished isn't an option....
Good decision! And even if a custom-made transformer is beyond reach, all may not be lost just yet!
I did look at the design of the power supply yesterday, trying to figure out why it is made the way it is...and I think from a perspective of modern electronics there is room for improvement/simplification.I see no technical need for a split 10V, 24V power supply. I guess the B&O designers did this to avoid interference between the logic board #3 and power-hungry parts in the analog circuit (motors, solenoids, the Byzantine reed relays, etc). That's not really needed. You could safely run the BG4000 on an off-the-shelf 2x12V secondary by replacing 2TR6 with a modern 6V LDO regulator. That costs you $2 and 5min of time. The transformer you could get from digikey for EUR20.- to 40.- max (and those are even 115V/230V dual windings on the primary!).
What it boils down to, however, is the real estate you have available for the trafo. What is the size of the current transformer? From pictures I'm estimating that you have at least 70x70x40mm of space available....that's tight. 80x80 or even 85mm would be better and would allow the use of many standard toroids.
Ok......couple of measurements
Another...
and another....
Thanks! ...but in this case I would have preferred actual dimensions in mm...
Oh well, as an optimist I gather that following plot of Beogram land (in light red) is available for redevelopment?
I reckon that's good 10x10x4cm! That's plenty for a standard 50VA toroidal transformer, which is usually around 80-83mm in diameter and 35mm high.The fuse box probably has to go as it is a total waste of space and can be redone in a quarter the size. Also it should leave enough space for a EMI/RFI line filter, which is something I'd strongly recommend this day and age considering the quality of the grid. A good branded filter costs some $10.- and is a worthwile investment and improvement.
I'd go with a standard 50VA toroidal transformer from digikey, Farnell, Mouser, etc. with 115V/230V input windings and 2x12V/2x2.08A secondary windings.You connect the 2 secondaries in series to supply the 24V circuitry and use one 12V coil (just like a center tap) as supply for a 6V/1.5A LDO controller or, if you wish, for an adjustable LDO, eg. LM1086-adj. It needs just 2 capacitors and 2 resistors as external components and replaces the 2TR6. A small heatsink for safety might not be a bad idea too.
But before going down that road and ordering an actual replacement transformer, I suggest you really take some time and confirm the true space available -- preferrably in 3D, ie. make sure that there is no parts on the top cover that limit the available space or the height. I don't have a BG4000 on hand, so I can't check what really is or is not available.
Hi Craig,My Beogram 4000 transformer ordeal was with my very first Beogram 4000 turntable back in 2015. My post showing it starts at the bottom of this Beoworld page.Being in the USA I used a company here named Toroid. They had me work directly with their engineer to design what I needed and what would fit.The resulting toroid was 71.1 mm in diameter and 35.5 mm in height. A couple things to note about the design for mine are that I opted for a US-only voltage so I don't have the voltage selection for different countries. I also didn't realize at the time that the 240 V secondary was necessary to power the neon strobe. It turned out quite well for me and that turntable is one I still use here at home. The link to my Beoworld post on it shows where I created an LED replacement for the strobe and that works great. I remember the cost wasn't bad for a custom built transformer back in 2015. About a year later Rudy used the Toroid company to build a replacement for a Beomaster 4000. That was quite a bit more expensive.For your case it would be worth asking the Toroid company for an estimate. Someone else on the Beoworld Forum found a place in Australia that custom builds toroid transformers. Surely there are places in Europe that do that. I had written down this name: Canterbury Windings, obviously in the UK. I never got any more information about them but since they are in the UK I would reach out to them and see what service they can provide.-sonavor
sonavor: The resulting toroid was 71.1 mm in diameter and 35.5 mm in height. A couple things to note about the design for mine are that I opted for a US-only voltage so I don't have the voltage selection for different countries.
The resulting toroid was 71.1 mm in diameter and 35.5 mm in height. A couple things to note about the design for mine are that I opted for a US-only voltage so I don't have the voltage selection for different countries.
Thanks for this! Did you have them make a 60VA version or the more common 50VA?
I guess for Craig it's also best to use a single primary with 230V and without any taps - provided he opts for the custom-made solution that is. 230V covers all of Europe and more than half of the world market. The 220V secondary for the neon lamp is not needed at all with 220-240 mains. Some 45-55VA for the 24V secondary and 5-10VA for the 9V secondary will be perfectly fine. I would probably ask them to add a self-resetting thermo-fuse. It doesn't cost much and adds safety.He can then disable the voltage selector, drop one of the primary fuses (which saves space and complexity!) and he has space for an additional line filter as I mentioned above.
It's no wonder that Rudy's transformer was quite a bit more expensive. It's a power-amp trafo with over 300VA and with all the taps from the original and they charge quite a bit for such gimmicks. Also, shipping prices from the US can be exorbitant. A few years back I ordered a refurbished motherboard for my notebook. Great price at barely USD30...but then the shipping was 100+ ... aaand to add insult to injury, since the total price was now over 100, I had to pay customs and duty!
The rated primary current was designed for 0.34 A and a nominal supply of 120 +/- 10% and 60 Hz. So that is a VA of up to about 45.There are two secondaries -
UO: 24.1 Vrms20.5 Vrms / 1.5 A
UO: 10.1 Vrms8.7 Vrms / 0.4 A
-sonavor
Found this that would fit the available dimensions....but the VA looks a little low at 30 and 1.25A output current? thing is I don't want to remove the voltage selector switch if I can avoid it.......