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
Oh yes, that was the "African" version of Beovox 1200 mkII. A smaller version of Beovox 3000 Type 6220, though actuallyquite identical to Beovox 2700 with the Peerless woofer and Seas 87H tweeter.Not a lot of photos or info available anywhere, so would be interesting to see more.
Martin
BC214, huh? You like to live dangerously, don't you?
BC214 has a max. Vce of -30V and you're getting dangerously close to that limit by turning the trimmer to one of the extreme positions! BC212 with Vce= -50V would have been better. (especially BC212B would be good because of similar gain (hfe) as BC154)BC214 should be fine as replacement for phono pre-amp transistors, though, because there you have a 24V supply.
But anyway, BC214 should be fine for testing in the power supply and as long as you keep the trimmer at middle position during first power-up....and provided nothing else is wrong in the circuit, of course.
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One more thing, which should normally go without saying:When you start the soldering work, visually inspect the solder joints in that part of the board first. If you find any cold solder joints (= damaged solder joints that cause intermittend contact), you should re-solder them. You'll know what a cold solder joint is once you see one.
rgds, manfy
manfy:BC214, huh? You like to live dangerously, don't you?
Erm ...... yes but not with audio equipment - thanks for the warning!
So as you first suggested rather go with the BC161 as that can handle -60V?
Regards
Anton
Yes, I think BC161 is a good choice here. It's the complementary type to BC141 and the voltage and current ratings are in a good range.
There's only 2 things that can kill a transistor: over-voltage and over-current. DC-gain and cut-off frequency are not overly important in this power supply circuit.In the amplifier circuit it's a bit different. There you do not want to stray too far from the parameters of the original transistor. A substantially different hfe or transistor characteristic might result in a noticable difference in sound quality or sound image - and that's the last thing you want in a good amplifier. It's especially annoying if you get an audible difference between stereo channels!So just keep the BC214's for the phono pre-amp that's causing you trouble. The transistors are the most likely culprits in that circuitry.
manfy:Yes, I think BC161 is a good choice here
Well Manfy you rock, thanks to your help and suggestions the power circuit is stable at 30V
It was the "BC154" that was the culprit, the moment the BC161 went in everything started working.
Reason why "BC154" is inverted commas is because it is not a BC154 transistor at all. It was in fact a SGS 87040 (but this had been covered up with green paint, had to scrape it off with a blade). Very little info about SGS 87040 but google says close to 2N708. Then I remembered that the pre-amp section has about 10 BC154's as shown on the schematic and circuit diagram. Well on my model 2318 they were all substituted with SGS 87040 except for the 4 in the phone preamp where they were subbed with BC159B.
Pic of my camouflaged 87040 transistor below. Would love to know why they did this thing with the paint? Inferior part they were disguising, attempt at hiding proprietary information ...
Now I'm onto the next mystery - where has my 9V supply gone for the radio circuit?
I'm getting 30V on the collector of BC141. Still gettting 30V when it gets to the input side of resistor #903. Output side 4mV. Desoldered one leg and tested, it is 1.2K ohm. While that was loose also tested #909 - thats 40.7K ohm. Can't figure out why the voltage drops so much.
Please let me know if you have any thoughts.
Thanks in advance.
Anton.
Glad to hear, that my suggestion regarding the two zeners and BC154 was right.Now perhaps a shorted 902 (100uF) or 904 (Zener)?
AntonvZ:Now I'm onto the next mystery - where has my 9V supply gone for the radio circuit?
Well the 13 hour post approval lag gave me time to figure that out and replace the other zener diode #904.
When I desoldered the original diode and tested it it gave OL readings in both directions .
At least the radio is working again, getting decent reception although maybe not perfect clarity.
Next up will be the dead right phono preamp stage but first want to test a theory I have about Beogram din plug wiring before I start changing things on the amp.
Dillen: Glad to hear, that my suggestion regarding the two zeners and BC154 was right.Now perhaps a shorted 902 (100uF) or 904 (Zener)
Glad to hear, that my suggestion regarding the two zeners and BC154 was right.Now perhaps a shorted 902 (100uF) or 904 (Zener)
Snap - bit of a cross post there (-:
Indeed you were right as always and thanks for all the help.
And as above right again, it was zener #904.
Congrats! Good job!
AntonvZ:Pic of my camouflaged 87040 transistor below. Would love to know why they did this thing with the paint? Inferior part they were disguising, attempt at hiding proprietary information ...
If those 87040 substitutes were mounted originally, it proves that even B&O picks any sort of substitute whenever there's a shortage of correct components But on the upside it means that you don't have to worry too much about using any cheap alternative transistors as a replacement.
Now that you have a stabilized supply voltage of 30V, you just need to adjust the idle current for the amplifier and you're in a base state for further works on the unit.
AntonvZ:Next up will be the dead right phono preamp stage but first want to test a theory I have about Beogram din plug wiring before I start changing things on the amp.
Ok, but don't waste too much time with it. It's very unlikely that there is something wrong with the input wiring, particularly since the left channel is working.
It's much more likely that you have a contact problem at the 'needle-talk filter' switch. 50-year-old switches do have a tendency to show oxidation buildup on their contacts. The circuit diagram shows that the preamp output is switched via that filter button. Just press it off and on a few times while an input signal is connected and if you hear intermittend sound then the switch is the problem.
If not, I'd start out with measuring the voltages at the 3 preamp transistors. Your service manual should show the nominal DC voltages and the one transistor where the voltages are off too far should be the source of the problem.
Just out of curiosity: what kind of device are you connecting to the phono 2 input for testing? Any standard turntable with MM pickup or a Beogram unit with Moving Iron cartridge?
manfy: Congrats! Good job! AntonvZ:Pic of my camouflaged 87040 transistor below. Would love to know why they did this thing with the paint? Inferior part they were disguising, attempt at hiding proprietary information ... If those 87040 substitutes were mounted originally, it proves that even B&O picks any sort of substitute whenever there's a shortage of correct components But on the upside it means that you don't have to worry too much about using any cheap alternative transistors as a replacement.
Not just any sort, really.B&O used RCA transistors extensively at the time. They were very good quality (I see them often and I rarely replace them).I'm sure they were offered at a good volume price, but I wouldn't call them "cheap", really.F.e. 2N5034/2N3055 were often replaced by RCA 60465 in Beomaster 1001/1200/1600;https://beoparts.com/2014/08/22/beomaster-1001-1200-transistor-rca-60465/An excellent component - but not one you will often see elsewhere.
Dillen:They were very good quality (I see them often and I rarely replace them).
Like my original post said this set has been in my family since new so they are definitely originals and I am sure that the one that failed was more likely due to an early act of stupidity on my part like a a shorted cicuit due to dropped solder, bit of wire snipped of from capacitor leads, multimeter tip slipping when measuring etc etc than an inferior part. And the rest of them of them on the PCB are still working fine, including pre-amp stage but more about that in my answer to Manfy in the next post.
I have learnt in a short time to treat working on electronics like open heart surgery. If you drop something you don't go on and don't switch on until it has been found. Also got myself two 50x50mm pieces of wood to act like spacers so that the set/board cannot touch the work surface where any of the above might have fallen.
Dillen:An excellent component - but not one you will often see elsewhere.
Yup had to google a fair bit to even find the scraps of info I got.
Best regards
manfy:you just need to adjust the idle current for the amplifier
Solid at 24mV
manfy:unlikely that there is something wrong with the input wiring, particularly since the left channel is working.
Nothing is wrong with the input wiring providing you plug in a Beogram on its original cord kinda proving my theory right.
To recap a bit - I have a 5 pin din to 2 RCA adapter cable, it works fine on both channels on QI and Tape with the following audio sources Ipod, Pioneer CD player and my Pioneer TT (but of course very softly on the TT which has no preamp)
If I use the same cable with the Pioneer TT (MM cartridge BTW) on QII the right channel is dead. Not intermittent. Dead.
You may recall from an earlier post that I recently acquired some other B&O toys, one of which was a Beogram 1001 with a busted stylus. So in the process of reading up a bit on the Beogram and looking at the circuit diagram I realized that B&O bridged left and right channel negative with the earth wire in the cable. The socket on the Beogram supports this, all the pins are bridged except left and right positive.
After a fluke chat with my vinyl guy I got put onto another guy who knew a guy who had a Beogram he wanted to get rid of. Turns out it was also a Beogram 1001 and I got it with a close to perfect SP14 stylus for +- 50 Euro. The rest of this TT looks like it got driven over by a truck, whole baseplate is shattered etc but now I have a parts machine.
So this afternoon I plugged my new SP14 into my nice Beogram 1001, plugged it into QII on the Beomaster 1000 and both channels worked perfectly. Listening to opera at 45rpm - not so nice - but very entertaining.
Thank you however for the above advice because I think I will need it shortly for my Beomaster 1001. There the one phono channel is intermittent. Its either the phono hi/lo gain switch next to the input socket or the phono selector switch, fiddling with either will make it work for a while but then the one channel just cuts out. Early days yet, haven't even figured out how to open that one.
Now I need to really beef up on the Beogram, figure out how to get into it, free up the fine speed adjustment which is seized solid and probably replace the belt so that Pavarotti does not sound like a duck on acid in a helium tank.
Dillen:Not just any sort, really.B&O used RCA transistors extensively at the time. They were very good quality (I see them often and I rarely replace them).I'm sure they were offered at a good volume price, but I wouldn't call them "cheap", really.
Oh, I'm sure you're right!I just read up a bit on the history of the transistor and I'd say it's safe to assume that there was no such thing as a "cheap noname transistor" in the 1960's. Certainly not for silicon transistors because they only started to be commercialized in the mid sixties.Ultra-high volume low-cost production probably started only decades later.
I just came across a transistor crossreference book from 1963 and it contains exclusively semicon makers from the US, Japan and various European countries.
Excellent! So you have a fully functional Beomaster 1000 now.
AntonvZ:If I use the same cable with the Pioneer TT (MM cartridge BTW) on QII the right channel is dead. Not intermittent. Dead. [...] The socket on the Beogram supports this, all the pins are bridged except left and right positive.
[...]
The socket on the Beogram supports this, all the pins are bridged except left and right positive.
Unfortunately this does not explain why the Pioneer turntable doesn't work on Q2. If anything, it's strange that both channels work on Q1, because on Q1 pins 1 and 2 are not connected, which suggests that the GND signals of the pickup coils are connected to GND in the 5-pin DIN to RCA adapter. All 4 coil connections are passed through separately to the output. I checked several diagrams from consumer turntables to high-end products.
Anyway, that's nothing to worry about now. It's just food for thought in case you encounter the same issue on other equipment.
Enjoy your restored Beomaster!
manfy
Check the condition and tension of the contacts inside the Q2 DIN socket.
Dillen: Check the condition and tension of the contacts inside the Q2 DIN socket.
Big thumbsup! That I can believe without giving it a second thought. The 3-5mV you get from a MM pickup can quickly turn to nothing when encountering the slightest oxidation on a 50-year-old socket.Luckily those panel-mount DIN sockets are still readily available in any electronics store for little money if the original socket is beyond repair.
Hello, I'm new in this site
I need help with beomaster 1000, the wiring at my house is different from your on the pictures! Can you add detailed photos for the cables which are connected to the large capacitor 3000 50v and those which are below? Thank you C
Hi Grissa, unfortunately have no detailed images of that part of the Beomaster from when it was disassembled and before I started replacing caps. Suggest you hunt around on the web and in this forum.
If you go through my post thread, the user Dillen is very knowledgeable and helpful. Could never have repaired my unit without his help. And Manfy, he also helped a lot.
Good luck with your project.
Grissa,
What are your concerns exactly?
One thing to keep in mind is, that Beomaster 1000 has positive ground.
The wires at my beomaster are soldered to the + capacitor and I'm not sure it's right ... Brown, black gray and orange .... it's anything and only photos on the 50v capacitor and the transistor side who can help me follow the wiring. Thank you
Thanks for your intervention.
If you can see on the photos ... The positive of the capacitor there is the black which comes out of 6.3v of transformers and orange, purple, 2 black, brown and a black white, gray ... They come from speaker and in capacitor negative a red that beeps if I touch the emitter of transistor 2n3205 next to it
How I can add some photos?
How I can add photos?
You need to add the photo under your profile first. Then when writing a post, you can press the film strip symbol - it will take you to your photos. Beware that it does not work in Safari but if you use Chrome there should be no problems.
Thanks for help