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Old 11th November 2007, 04:33 PM   #1
pfcs49 is offline pfcs49  United States
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B&O 8002 turntable Post #1
My B&O 8002 turntable has started to spontaneosly lift its tonearm and return it to the storage bay/end playing occasionally, usually when its 2/3-3/4 of the way thru a recording. I have the repair manual/wiring diagram, etc, but it gives no clue of the logic the microprocessor uses to initiate the stop cycle. Can anybody coach me on a fix or tell me who would have knowlege and be willing to share it? Thanks phil


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Old 11th November 2007, 04:49 PM   #2
Magura is offline Magura  Denmark
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Try ringing Anatech's bell. He has been around the repair business for quite some time, and is extremely skilled.

http://www.diyaudio.com/forums/membe...o&userid=15917

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Old 11th November 2007, 06:29 PM   #3
pfcs49 is offline pfcs49  United States
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As a new member, I am prohibited from emailing members. Perhaps he will notice my post. Thanks, Phil
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Old 11th November 2007, 09:42 PM   #4
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Old 11th November 2007, 10:26 PM   #5
anatech is offline anatech  Canada
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Hi Phil,
Sorry for the delay in answering. Welcome to the forums!

I think they used an optical sensor for arm position on this one. Dust can really mess things up for you and cause a false trigger. Also watch for intermittent lamps or connections.

Now, these are fun to take apart. Take your time and be careful. Simply clean the dust out with a soft paint brush or compressed air at no more than 50 psi, held back at least 10". With all that dust, you will not want to be any closer.

You can use a Q-Tip (cotton swab) with some iso - alcohol on it to clean the lamp surface. The photo interrupter should be cleaned carefully and gently with water at the most.

Let us know how you make out please.

-Chris
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Old 22nd November 2007, 08:37 PM   #6
pfcs49 is offline pfcs49  United States
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Thanks for responding. Things are a little out of control here as the system is stored while the room undergoes a change. I'll be back to it in a couple of weeks when I want to see what is supposed to cause the shut-off/return-tonearm response. I don't know if it's caused by the increased reflectivity of the inner area of the un-cut vinyl as sensed by the light beam on the secondary arm, or by the higher rate of change/inability of the tracking drive to keep up when the arm tracks the end-of-record groove. If it's not caused by the photo setup on the arm, I'll try cleaning the photo servo under the platter that relays tonearm position to the processor. I'll let you know. phil
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Old 22nd November 2007, 10:20 PM   #7
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Quote:
Originally posted by pfcs49
Thanks for responding. Things are a little out of control here as the system is stored while the room undergoes a change. I'll be back to it in a couple of weeks when I want to see what is supposed to cause the shut-off/return-tonearm response. I don't know if it's caused by the increased reflectivity of the inner area of the un-cut vinyl as sensed by the light beam on the secondary arm, or by the higher rate of change/inability of the tracking drive to keep up when the arm tracks the end-of-record groove. If it's not caused by the photo setup on the arm, I'll try cleaning the photo servo under the platter that relays tonearm position to the processor. I'll let you know. phil
Hi Phil,

If my memory still serves me, there is a slotted rail with bulb and a photo transistor (today it's called a linear encoder) which tracks the speed that the arm moves across the record. In the leadout grooves the arm picks up the speed change and the circuitry senses this and calls (what we call at work) endpoint; lifting and returning the arm.

Logically if it's tracking the record at all, the encoder front-end (bulb/rail) is functioning properly.

Once again(from memory, I haven't pulled out my schematic) but, the pulsing from the encoder might need to stay in a defined range, so it might sense when it goes to slow as well. This would mean it also detects if the arm doesn't keep up.

This all leads up to checking the belt that drives the leadscrew that controls the arm tracking. I remember them slipping. It might be possible to adjust the motor mounting to tension it. If this is in fact happening you can see the arm stop tracking (by the angle relative to the parallel optic arm).

I serviced these turntables when they were still in warranty. A bit more details as to the clues and I might be able to pin point the problem.

Mike.
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Old 5th December 2007, 10:09 PM   #8
anatech is offline anatech  Canada
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Hi Mike,
Quote:
This all leads up to checking the belt that drives the leadscrew that controls the arm tracking. I remember them slipping. It might be possible to adjust the motor mounting to tension it.
They sure do!

It's second nature to check any belts you see for slipping. I've replaced many over the years in these. I normally ordered and installed the entire set to keep the customer running for 10 years or so.

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Old 9th December 2007, 08:33 PM   #9
pfcs49 is offline pfcs49  United States
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Set up again and made some tests:
If while tracking a record, I lift the arm w/an L shaped paperclip, I can accelerate it towards the inner grooves-certainly moving it faster than it does when the record ends-and nothing happens except the tonearm base moves pretty fast trying to catch up.
If I put white paper or a mirror under the light source in the sensing ("slave") arm, nothing happens.
So I don't think the slave arm or the tonearm angle sensors are involved in end-of-play-tonerm- return logic. Maybe the leadscrew rotation sensor counts turns? If that's how it works, then I'd suspect a problem in the controlboard. I've seen several references to replacing some of the caps in these board. Anyone know if a leaky cap could be cause in this matter? Or anything else? Or who would know and be willing to tell. (for a resentment at no charge, try asking the SoudSmith ANYTHING!) (Soundsmith is auth B&O svc guy/makes new cartriges for TT) Phil
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Old 10th December 2007, 11:01 AM   #10
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Quote:
Originally posted by anatech
Hi Mike, -Chris
Hi Chris.


Quote:
Originally posted by pfcs49
Set up again and made some tests:
If while tracking a record, I lift the arm w/an L shaped paperclip, I can accelerate it towards the inner grooves-certainly moving it faster than it does when the record ends-and nothing happens except the tonearm base moves pretty fast trying to catch up.
If I put white paper or a mirror under the light source in the sensing ("slave") arm, nothing happens.
So I don't think the slave arm or the tonearm angle sensors are involved in end-of-play-tonerm- return logic. Maybe the leadscrew rotation sensor counts turns? If that's how it works, then I'd suspect a problem in the controlboard. I've seen several references to replacing some of the caps in these board. Anyone know if a leaky cap could be cause in this matter? Or anything else? Or who would know and be willing to tell. Phil
Hi Phil,

I dug out my schematics to refresh myself; It's been s few years. I need to think about it a bit more and spend more time than I have now, but it seems to be a combination thing going on to trigger the return. there is the encoder that tells it where on the record it is and either the arm wand looking at the reflection from the record or the speed of the arm moving towards the label. I just have to examine the schematic and think about it.

I'm trying to do this from memory.

I'll post the schematic, which is always a challenge. What series is your turntable? 5513, 5523, etc.?

Mike
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