Hi

I bought a Beosystem 5000 including Beogram 5005 record player. When playing the records I noticed that the right channel was consistently at lower output than the left. With Sennheiser HD-25 headphones it's noticeable, but even clearer it can be seen in this screen capture:
http://img72.imageshack.us/img72/535/picture1hm3.png

I thought it was the MMC4 needing replacement, so I bought the Soundsmith SMMC4. New stylus improved the sound by a large margin but the channel output inbalance did not disappear.

Swapping the RCA cable did not remove the problem, and reversing channels with RCA adapters had the lower output switch to the left channel of course. Can anyone give me some ideas what to check next? I really want to get rid of this problem, rather than having to  invest in a mixer with settings fine enough to compensate for the lower output on the right channel.

Kind regards,

Vilhelm
 

You seem to have checked everything else so check the internal resistance of the mute switch in the deck.

Pardon my ignorance but how do I do that? I have the service manual, but did not find this in it.

http://forum.beoworld.org/forums/thread/39770.aspx <-- This topic the poster has a similar problem and it turned out to be "the mute switch" as you wrote. I wonder, how do I correct it?

I don't think you can clean the contacts since it is a sealed microswitch. Ask your dealer if the part is still available. Pt Number 7400293

Very kind of you, thank you! Does anyone have any ideas where I can buy the parts online? I am pretty sure my dealer does not order them because B&O center in Helsinki no longer supports vinyl players :-(

Vilhelm 

I too have the same problem - symptoms the same, one channel very low then when the arm lifts, momentarily, there is the full level of sound.

Is this muting switch available anywhere. Part number 7400293

Given that I don't have a servicing agent in this state, can anyone recommend a dealer, in any country, who might be prepared to order the part.

Or maybe Martin or Chris has one ? Do they come in any of the other tangential turntables ?

Tasmania, Australia is a long way from anywhere B & O.

Thanks, I look forward to hearing from you. Merry Xmas to you all.  

The same muting switch is used in all the "lightweight" tangentials from the BG3000 onwards.

Surely the Aussie dealers will supply this part by post??

Couldn't you just bypass (i.e cut off) the switch until you get a replacement? Most other turntables in the world have never heard of a muting switch, and they still won't destroy the loudspeakers with a Bang, so to speak :-) Not quite as sophisticated, but at least the levels would be right...

-mika

I'd be happy to bypass the switch temporarily if I knew the location and the method of bypass.

I'm an amateur at this, hence the requirement for the information. As far as dealers in Australia go, there are only a few and there is a reluctance to sell a part to an amateur not connected with the dealer or service network - very protective as a rule.

Thanks for the replies

I made an attempt to " bypass " the switch, inasmuch as I have tried the unit with the switch  fully depressed.

No joy - there was no sound from either channel.

With the switch in the out position, the right channel working well, the left barely audible, back where I was.

When the arm lowers to the surface, momentarily the left channel will work, same as when lifting the arm, again only momentarily.

When checking the switch according to the service manual, on page 5-4 I've no idea what the heck I'm doing really. I turn the arm until the muting switch just opens...............than whay ? The manual doesn't tell me what I'm looking for or checking.

The arm has to move the switch perhaps .7mm until a reading goes from OL to 760 odd ohms, then to .3 ohms or less.

Does this point to the switch being faulty ? 

How is the bypass of the switch effected ? Which pins are joined ? 

I am not totally confident of my soldering capabilities to take the muting unit right out of the loop and wondering too what effect this is likely to have. In the toolbox is some thin wire similar to that from the cartridge - would this be best ? Should the duff switch be removed for this to be effective or can it be left in place ? Is the switch actually faulty ?

The service notes neglect to mention the resistance required with the muting switch. The notes read as if this vital piece of information is missing. ( page 5.4 ) Or is the function of this test to determine whether the switch is working or not ?

Happy to speak to anyone on the telephone, in any country, at my expense, in an effort to complete my task. 

Thanks in advancel. 

Well, actually my 5005 is lower on the left than the right.

Please read my previous post, I'm becoming confused about what and how to check.

I'd sure appreciate some guidance/assistance/help. 

Thanks. 

Unfortunately I don't have the repair manuals nor have I ever seen one of these machines myself, but a switch should be just a switch. If it reads anything else than open loop or 0 ohms depending on the position, there has to be something wrong with it (BTW, be careful when measuring! Some cartridges might not like the measurement current of some multimeters, the windings are unbelievably delicate!).

I'd probably find out from the service manuals whether the switch is open or closed when the player is playing, take the switch out and then add the appropriate jumper wires. Leave the hair thin wires coming from the tone arm alone if you can.

I believe the switch contacts have corroded and make bad contact. The muting switch I know (in my Beocenter 2800) was just an open slider and indeed required cleaning. Relays and switches that actually switch any significant current are somewhat self cleaning due to the current that flows through them, but that effect won't help with the miniscule current a cartridge is sourcing. With some persistance, It might be possible to crack the switch open, clean the contacts and still put it back together in working condition, but I believe that's more like the stuff that restorers of 1920's radios are doing... these micro switches must still be available somewhere.

thanks tournedos, I've sent you an email.

I need to be advised on the best/correct way to remove the old switch from the PCB and next jump which terminals on the PCB.

Thanks. 

 

UPDATE : I've now doused the muting switch with contact cleaner, then tested between the terminals suggested in the service manual.

Switch depressed - 0 ohms, no change there.

Switch out - 1m ohm rising to OL

Throwing caution to the wind I've now disassembled the switch. There is a metal cover, dab painted on one side. The metal cover will move in an arc aprox. 20 degrees either way. This must be for other applications, not B & O.

Once removed, there is a lever/tab each side which wil gain access to the workings of the switch. There is a spring in the centre and on the white switch protrusion ( I'm not good with correct nomenclature in this field ) are two sets of dual pronged terminals.

When the switch is depressed, it contacts with what looks like a bar in the base of the switch. I'm in the proces of cleaning this thoroughly, then reassembling to test once more.

 

If I don't get a result this time round, than I'd appreciate someone looking at the  wiring diagram ( I'll send it to you if you don't have one ) and advising me to bridge which terminals on the PCB for the ultimate removal of the muting switch from the PCB.

 

Whilst an electrical novice, I'd like to think I have skills in other areas which can prove useful. I'm not afraid to have a go at repairing this. From other posts I've perused noone else has dismantled a muting switch........

If I can get any sort of decent image of the component parts of the microswitch I'll post it on here. 

 

Thanks, I'll look forward to hearing from you.All the best during this festive season and for 2008 too !

Okay, I give in on making the switch operate.

Could someone please show me which wires to bridge to cut the muting switch out of the circuit. Looking at the wiring diagram, it seems to me that if the switch is out of the picture, then there is nothing to impede the signal - is that correct ?

The switch appears to operate in such a way that when in " play " mode, the switch is in the OL position, or fully out, therefore if the switch is negated, removed or neutered  the situation doesn't change.

Spent serious time with this thing now. 

Thanks. 

Here's a couple of images of the switch pulled apart. It is not that difficult to dismantle, or reassemble.

 

 

 

It would be great if there is a tech person out there who can confirm my thoughts on the removal of the switch, ie if the switch is removed, the muting circuit does no longer operate, but all else should work fine.

Thanks, I look forward to any replies. 

If my reading of the circuit is correct, when the switch is depressed (muted) the output of both channels is shorted to ground. Therefore removing the switch completelyshould disable the muting function but the deck should work.

Seconded. The switch is connected a bit funny, but from what I can tell it short circuits the cartridge together in versions without a built-in RIAA preamp, and shorts the midpoints of a filter stage to ground in versions with built-in preamp. In either case, simply leaving the switch out should eliminate this possibility for channel mismatch.

Anyway, keep the volume low when experimenting. I don't know why B&O uses these muting circuits when all the others I've seen don't, but it's possible that the decks make a louder than normal "pop" when lowering/lifting the stylus. Or maybe it's there just for perfection... 

The switch might also double as a counterpressure for the mechanism, do consider that too before throwing it away.

Well, it's been a long time since I've addressed this issue here, but now the problem is all gone in my workflow of digitizing vinyl to WAV files

I admit being a noob when it comes to how these old amps work, and as there was bridging between the line in and line outs I used the headphone jack for listening and digitizing my vinyl collection. It was with the headphone jack that I noticed the channel balance error that I described when I started this topic.

Now, I just acquired two Genelec 8030 speakers and as they are active I removed the metal links, to disconnect the preamp from the  poweramp and use the line out for the speakers (can't use the speaker outputs obviously since those 8030's are active speakers). Now, using the line out, the channels are in absolute even balance as measured with Audacity when I digitized vinyls today.

So, something's wrong with the headphone output but that doesn't matter anymore to me as I've got around it :-)