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
I have three 800s and one of them has sort of a ghost in the machine symptom from time to time.
The left channel will loose some volume. I've tried diff phono inputs externals and its not the amplifier.
The CD and radio are fine.
Its not the cartridge as I've got extras and they all do it.
It seems to be realated to how long its been on. The fix is to turn off the turntable power for 10 seconds and then all is fine for hours. Then it will happen again.
Just curious what would cause this? And if I have to send it out is soundmith the best one to send it to in the USA?
THanks
I think some genius on AudioKarma suggested it might be a fault in the muting relay, but he is delusional
Well I'll take that with a grain of salt then.
Just wondering why a quick power off fixes it for a long time. Probably not heat, maybe a capacitor. I think the muting relay is to turn off the input when parked, that works fine.
The muting relay does not break the signal paths.It merely grounds them.
There are no electronics in the signal path at all.Any sound related problems will have to be caused by the cartridge, the internal and/or external signal cablesor the amplifier and speakers it connects to.
Martin
Thanks Dillen!
Well I only tried two different carts in it. It is possible they are both weak as they are old.
I swapped the cables and finally the right channel went lower in volume. Which makes it something from the Cart to the phono preamp connection.
I wonder why cutting off the power to the TT for 10 seconds fixes it for like 5 hours of play? If its the cartridge do a voice coil develop a charge which is then sort of reset if you power it down for a few seconds? Just trying to understand why it develops over a period of play time vs just being that way when I play the first record. Usually takes hours and the fix takes a few seconds.
RAJOD:I swapped the cables and finally the right channel went lower in volume. Which makes it something from the Cart to the phono preamp connection.
Or the preamp or the amp
Collecting Vintage B&O is not a hobby, its a lifestyle.
No not the preamp, I have tested with 2 different preamps same result. And other components hooked to amplifier CDs, other TT run fine without channel drop.
Bad connection, solder or pressure. Cracked insulation... Making condensator to somewhere on the line... ?
blah-blah and photographs as needed
I have a third cartridge I can try, that will rule out it being the cart. (I hope its the cart)
I would hope it's NOT the three cartridges.
That would mean I had three good cartridges and one problem to solve. Don't you have multiple turntables?
Lol me too but I have plenty of mmcs. Three mmc2s four mmc3s and once mmc4.
I confirmed it is the turntable and not the cartridge today. I put the mmc2 in another beogram downstairs and it works fine, I took a good mmc3 and after a few hours the left channel dropped in output by 60 percent at least.
Funny thing is the fix is fast, just power it off for a few seconds and its fine for maybe 5 hours of play then it will drop the channel output.
That does not sound like a loose connection, why would a loose connection be fixed by powering it off?
RAJOD: That does not sound like a loose connection, why would a loose connection be fixed by powering it off?
Something moves when you do that.
--mika
Nothing moves when I power it off. The turn table does not have a power on/off. I can do it at the wall, the power filter or from the amp. Any will do the trick. Sorry no cigar!
Is the Beogram the only thing that is powered off ?
I've tried it via Beogram plug, or from amp, or from power strip. Results all the same, it fixes the TT for like 5 hours then once channel goes dim like 1/2 volume. Turn it off/on and Bam back in action.
If it worsens I probably will send it out for a fix. Just seeing who here can come the closest to what could be causing it. I'll report back here if you are the winner.
You verified the cartridges are good by testing them in other Beograms with different amplifiers. Did you take the problem turntable and test it with one of those other amplifiers?
-sonavor
I still suggest muting relay.
I realize it grounds the + side to ground only while muting and shouldn't logically be the fault, but in that it cycles and moves it's contacter whenever you end play or shut the deck off AND that's when the situation resolves, can't help wondering what might be going on inside.
I think you can probably stick a little piece of paper between the contacts with the plastic cover popped off the relay to pretty much eliminate it as a cause.Just sayin.
The muting relay is mounted on a small seperate pcb,sited at the rear left hand corner of the machine.Although as other's have rightly stated,the relay doe'snt interupt the signal path,there may be a poor solder connection on the pcb,possibly where the fine wires from the pu connect,or the output cable? I suspect that when you power off,then on again,the small mechanical vibration as the relay reset's may be overcoming the problem.
Next time it happens,try gently tapping around the rear left hand corner of the case.If the fault clears,I rest my case,otherwise "beam me up Scotty"!
Nick
Thanks Nick I'll do that for sure. Yes when I turn it off I am not even touching the TT so any vibration would have to be some kind of mechanical switch in the TT. Which is what the mute relay is I gather.
It just cut out again but this time I tried to jiggle all the wires coming out the back to see if it would kick on. Nope, it seems to be electrical in nature and not mechanical. A 1 second on/off and its fixed. So much for the loose wire theory. Probably has something to do with that mute relay. Like it builds up a charge in it and powering it off resets it somehow. Strange for sure.
When it comes to old electronics, nothing is starnge
Put a voltmeter across the muting relay coil and see if the voltage changes during play.
It occurs to me that the muting relay (should) cycle whenever a record ends but Rajod states it takes ~5hrs for the defect to happen.
Does the relay work when the tonearm goes to the parked position?
How about putting a Flukemeter in record mode across the problematic output and seeing what changes after several hours? Or, checking the values of both channels when normal, and then again once the problem appears. This should include the signal pairs as well as the signal to chassis ground values.Knowing how and what changes would be good diagnostic information and may provide a clue.
Yes the mute relay works in the parked position. However one time when in parked position I could hear static coming out of the speakers. Which would point to the mute relay not quite muting in the parked position. But that has not happened in months.
Is that a electrical switch or mechanical? Cleanable or just through it out type part?
The muting relay has mechanical contacts, operated by a solenoid.If the controlling electronics fail, the voltage to the relay coil could be creeping up or down over hours, causingthe relay to "slowly" activate its contacts.It's a theory, at least.You can also desolder the relay and remove it completely. The Beogram will play without it though you will thenalso hear a little noise when the needle lands and lifts but it's not particularly loud or annoying for a test.
How about I just spray contact cleaner on them to start?
I am not sure how that relay works but does it not mute both left and right channels at the same time? It only seems to affect the left channel and only by around 50 percent in apparent drop in loudness. Wonder how its affecting just one channel and not both? Its a mystery.
The bronze contacts inside the relay are separate.One of them could even be bent or partly stuck.
Contact cleaner is good when you can NOT get closed mechanical contacts to conduct current.It will not prevent closed mechanical contacts from being conductive.It does not isolate, it losens oxidation (and doesn't remove anything, it merely losens the junk and allows it toshift around and in the best of cases it doesn't add too much to the mess).
I took apart one my of parts 8002s. Never opened one up before. I thought someone said the mute relay was in the top left corner but the only switch I see is under the tone arm on the right side.
I've labeled a few things that I am not sure what they do. If someone could help fill in the blanks would be appreciated.
I could not find the sensors that are somewhere behind the tonearm. I took a picture of the backside of the tonearm, where would they be?
Item "A" is OTR2 and 3 in the schematic. You can see more details here.
Item "B" is OIC1 in the schematic. You can see my recap of the two electrolytic caps here.
The third picture is not a relay, it is listed as the SO Switch in the service manual and controls the set down position of the BG8002. You can see a picture of the adjustment here.
I'm not sure about your fourth picture.
Thanks Sonavor,
Is the mute relay/switch even visible in my photos? Just wondering were it is.
Sonavor, I noticed I have a missing part of two of my 8002s. That little spring you have in the picture. I need to fasten the top plate better. I just temp used a little duct tape folded in 1/2 but its a little too thick. How did that 3M work out? Where did you get it?
I'm thinking just get a spring from a hardware or maybe a pen to substitute for that spring of unknown function.
" Under the aluminum deck panel however, there is a small spring on the left side. I guess it was for grounding. Maybe for anti-static? In any case, don't forget to put it back in place before resealing the deck with new double-sided tape."
Yes-any small spring like a shortened pen-spring will work to act as a ground for the trim-plate.
The muting relay is in the DIN socket assy in the upper left corner, above your red A. You need to dismount it and turn it over to see the relay inside. It has a clear plastic cover. Be careful of the 2 lightweight coaxial leads soldered to the little circuit board. They can only tolerate a few bendings before breaking off and are challenging to repair!
Aside: is there any way to edit your own posts on the forum?............YES!!
What I'd edit is to get clarification about the spring you saw on a picture i don't find in this string.
Yes. There is supposed to be a captured grounding spring under the platter trim-plate.
Also, the screw in the shadowy tonearm picture which isn't very distinct is (if it is brass, ~7mm head, has a "V" groove in it's waist, with the visible rod engaging that waist) is the adjustment for centering the parked-up tonearm position when the arm is not released and under servo-tracking control, as has been previously mentioned.
pfcs49: Aside: is there any way to edit your own posts on the forum?
Aside: is there any way to edit your own posts on the forum?
Yes, on your own posts...the "More" drop-down menu should have an "Edit" menu item like this -
Thanks, right now I am getting oriented with the inside of the unit. Before I go looking at the circuit diagrams I like to know what purpose of the parts are. I don't totally understand how it works. . Before I attempt any fixes on my own I have a ways to go education wise. Thanks for the help. The parts 8002 is sort of a learning TT for me. Can't ruin it as its already broken.
The DIN socket on one of my working ones must have a loose hold down screw. If I grab the cord plugged into it I can jiggle it easily. On the parts 8002 that same DIN socket is very solid. Wonder if that could be part of the issue with the channel that drops in volume after hours. Maybe one of those thin coax leads you mentioned are weakened from it being a little loose. Just a guess.
Also do you know where the sensors for the worm drive are? I guess they detect if the tone arm angle changes then sends a signal to the worm drive to turn.
BTW what is the purpose of that spring ground? Seems to work without it.
The spring is to allow the metal surface discharge static - see here (towards the bottom of the page).The 3M double-sided tape is what you get at auto part stores. I think I purchased mine from Amazon though.
The DIN socket/muting relay assy (8005044 on wiring diag) is secured by a single screw and two curved tabs that hinge up/out of the base after releasing the screw. If the looseness is from the screw, the entire assy will be loose. If not, then something about the socket inside is wrong. This should be checked, especially given your complaint.
Looking at the the long brass worm-screw from the normal/front perspective, the sensor is at the right end; there is a shutter-wheel on the end of the screw. The sensor is U shaped, with a light source and a photo-sensor. The adjacent motor and belt turns the shaft and the sensor sees each slot in the wheel; the signal goes to the processor which is the brain; it counts and keeps track of velocity and position of tonearm.
The sensor, light source, and light slot for the tonearm angle is in the under/front area of the tonearm assy or tonearm carriage as I call it. As the arm moves out of tangency, the shutter diminishes the light to the sensor and the processor responds by (slowly) turning the arm motor. AFAIK, the 8000/2 B&O only move forward in the groove; I think my Yamaha PX-2 is bi-directional.
A good thing for you to do would be to take your "parts" unit down to the point where the entire upper case and covers are gone. You can now lay a piece of corrugated cardboard over the area where the main circuit-board will naturally want to return to; this will insulate it from the electronics and steel base below it. Remove the control pad and the transformer from the case. Reconnect the ribbon wire for the keypad (pay attention to how it should be and don't get the ribbon-wire 180*/backwards!). Plug the transformer to the main board being careful that it plugs into the terminals correctly (the terminals are equip-distant so you can plug it together incorrectly when the case isn't there to only allow the right orientation. In this configuration, you can put a disc on the platter and play it-even through the stereo. You can swap things around to see if they work or not. Everything is pretty accessible for doing electrical tests. The voyages are low enough ton not be a safety worry. You are better off working on this unit and bringing it to life and heath. Once done, you will have a much clearer sense of the bigger picture and be ready to move on to the others, otherwise, I'm afraid they will all become parts units!
The spring's purpose is proper electrical engineering-to bring the major metal parts of the unit to a common ground plane, which includes dissipating static among other things.