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
Hello,
first post here in this wonderful forum. I started recapping and fine-tuning my BG4000. This beauty came from UK (I live in Italy) around 2005 in terrible conditions because of a bad packaging. Luckily nothing was broken but many parts were disassembled including the arm mechanism. I was able to put everything in place and let it work for many years since then.
But at a certain point it began to develop strange issues: self power-on, 7" not recognized and other little gremlins. Ok, time for a total recap and a tuning following service manual.
Recapping was done with Vishay, Panasonic and Nichicon electrolytics. One of the main unipolar caps was shorted and others were out of specs. Tantalum were OK but I replaced with electrolitycs. Now the motor spins fine and quiet, sine-wave is clean both at 33 and 45 rpm at 6,2Volts (@33), no more self-power on.
But I have a new issue: the two dial scale lights self-power on when I plug the beogram to mains. They're always on, even if I press OFF . Other functions are correct (strobe light, motor, arm transport power On and OFF).
Any suggestions or ideas will be much appreciated..
Hi
I am currently going through this exercise and I'm pretty sure I have the same problem....I have discovered that the reed relay 2MS2 24vdc contact is permanently on the closed condition, therefore illuminating the scale lamps on power up, they should only illuminate when the relay coil is energised. It looks like the only solution is to replace the reed relay, this will be very tricky as the relay coils are very delicate...the connecting wires are hair thin and graet care will be needed...you, and I, will also need to source a replacement reed switch of the correct size, wattage and Normally Open (I think) shelf condition......good luck, and post pics ;¬)
Quite common to see the contacts welded (or magnetized) together.
Leave the coil in circuit and pull out the reed element (glass tube with contacts).It can be replaced separately. Just find a suitable size.
Martin
OMG that sounds a difficult challenge... I will take some measures around the relay this evening. I guess there are no direct interchangeable parts on the market today :-(
Thanks for the tip.....I was going to remove the whole thing but will take a closer look now, can you take a look at this, I'm not sure what is meant by 15=20AT is it the magnetic field required to actuate the switch?
https://www.ebay.co.uk/itm/KSK-21-Reed-relay-Pswitch50W-Contacts-SPST-NO-500mA-max350V-KSK-1A52-1520/202412891200?hash=item2f20bf9c40:g:TmYAAOSwyGhbfuzB:rk:55:pf:0
Regards Craig
Got it......
AT means Ampere-Turns and is a standard unit categorizing the magnetic sensitivity of Reed Switches. The AT value is measured by centering the Reed Switch in a standard coil, to which an increasing current is applied. At a certain current (Amps) the Reed Switch closes by means of the magnetic field generated by the coil. This is the Operate (or Pull In) value, calculated as Amps x number of coil turns = AT. Reducing the current passing through the coil until the switch reopens, the Release (or Drop Out) value can be obtained.
Great! But i guess the original switches AT is unknown...or not?
Find some in the correct physical diameter to fit inside the coil.Don't worry too much about the magnetic parameters. The old switches weren't that sensitive and the coils therefore quite powerful.If a reed relay won't switch correctly, try rotating it a bit.
Thanks Dillen.
I took some measures around the relays, both in stand-by and On. Please see pic.
I did a test. Cut the red +24V wire from the reed "always on" switch and temporarily connected with the +24 grey wire on the other working relay: everything fine, lamps off when TT is in standby and lamps ON together with motor, strobe and arm pressing ON.
I ordered some new 2x14 mm glass reed contacts hoping they will fit and work. Many thanks to Martin who provided the possible solution.
I will update the post when the switches will arrive.
Actually, I think Craig was ahead of me with 20 minutes or so.
Yeah, sorry Craig..
But you saved both of us Martin, we didn't know the Reed tubes are replaceable It will be a late night, keep-calm affair (those tiny coil wires are so close to the tubes soldering points..) but let's give a try.
Hello again,
reed switches arrived and carefully fitted in the relays. Everything fine, now the BG shuts off and powers on how it should. Thanks.
Another couple of issues to solve, the main is 7" records not recognised. I will search across the forum before asking your help again.
Old reeds removed:
New reeds in place:
TT spinning again:
Good job......I'm also going through the detection arm issue so will keep abreast of each other. I do have a set of B&O training notes which provide a good amount of detail on these circuits (donated by solderon)….I have forwarded these to the site for inclusion in the service manual area in the fullness of time, however if you would like a copy now email me.
Craig
Thanks Craig. I could find the problem related to unrecognized 7" records. It was simply the spring that should press the corresponding button on the arm contacts board which was not low enough to be effective. Sorry I didn't took photos -I will do tonight- but it is the first button from right on the board (the only in grey color in my 4000, others are red).
A little bent on the spring, wich is flat on below contrary to the others that have a 45° angle shape, cured the issue.
But I have another question: when I keep press forward manually, the arm travels across all the rail (and this is correct) but does not have a safe-stop at the end.The arm motor keeps turning until I hold the key pressed, even if the arm it's at the end of the rail.
Shouldn't it have a safe-stop at the end of the rail? In auto-mode everything is fine: arm stops, lifts and go back.
Roberto
Just to complete, time for final adjustments before connecting to an amp...
- re-checked motor supply voltages, frequency and distortion. I lowered voltage to 6,10 volts @33rpm just (manual says not to go over 6,5V so I guess
6,1 it's a safe and good voltage). Clean sine-wave, no distortion here.
- checked arm alignment, adjusted arm height, and zero-balanced it.
- adjusted 7", 10", 12", start and stop button-springs positions and tested with different records.
Here testing the BG 4000 with a 10".
Late enough here, so will enjoy a good rum. Goodnight
Fantastic pictures. I had one of these BG's many many many years ago, in fact it was my first Bang&Olufsen item. I regret I sold it.
I do, however, prefer the 8002 now - much easier to maintain due to less electronics :-)
From the last two pictures it doesn't look like the cartridge mounts/mates to the tonearm connector correctly. Is that something you were planning on fixing?
-sonavor