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4002 tonearm lifts

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Jim Carr
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Jim Carr posted on Wed, Feb 10 2016 3:40 AM

Hi! I have a 4002 type 5503. The tonearm will suddenly lift then drop back during play.

It will do it usually once while playing a 33 and can do it any time. It is just a momentary lift then right back down without any input from me.

I have one other issue that is it wants to set down way before it reaches edge of the record.

Other than those two things it performs great.

Thank you for any help.

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sonavor
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Hi,
I haven't encountered that kind of failure yet but I would have to suspect an electronic problem rather than mechanical. You will need to dig out the service manual and check the circuit involved.

On the adjustments for the set down point, section 4-3 of the service manual shows that adjustment procedure. If you don't have a service manual you can get a PDF version of it with silver level membership on Beoworld.

-sonavor

sonavor
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Thinking more about your problem with the arm in the lowered position, then raising and lowering again...
I wonder if the problem could be with an unstable solenoid circuit. On those turntables, when the command to lower the tonearm is made, there is a solenoid that activates to move the mechanical lever to lower the tonearm. After the solenoid is engaged it remains in the activated position via a circuit that holds the solenoid in that state until the raise tonearm signal is received. Perhaps that holding circuit is dropping out, then comes back on its own?
Maybe Dillen has seen this type of problem before.

-sonavor

Dillen
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Dillen replied on Wed, Feb 10 2016 5:31 PM

Contacts in the up/down switch on the operating panel too close?

martin

Søren Mexico
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Check your main power lines for micro blackouts

Collecting Vintage B&O is not a hobby, its a lifestyle.

Jim Carr
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Update; Now that I have decided to find the problem and posted this thread it has not lifted during the last 3 lp's I have played!!.

I did remove the covers and platter and did see that the solenoid has been replaced as it had the plastic arm that liked to smoke them. I also see a lot of hand soldering from the factory that  looks cold. So I think I will re-solder the solenoid and maybe the dull looking connections to see what happens.

Thanks for all of your replies.

 

sonavor
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In resoldering I would just apply some new flux and touch up the existing solder joints. Don't just reheat the existing solder joints without flux. You may have already planned to do it that way but I thought I would mention it anyway.

-sonavor

Jim Carr
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Last update. I re-solderd the solenoid leads and it has not lifted while playing. Now playing like it was new!!

Thanks for all the help.

Jim Carr
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Well my problem is still there! After re soldering lots of connections and checking everything I know, I'm stumped. As I said the problem is very intermittent and lasts for only 1 to 3 seconds then nothing or up to 3 records then it will happen twice in the next.

What I have done, re solder connections, re cap every board, spent hours watching my scope to see what is happening and this is what I have found.

Solenoid Circuit starting with 1Tr14- no change at the base, collector rises to .81. 1TR15- base goes to .31, collector goes to 17! (checked many times) 1TR16ends up with 17 volts at base, emitter & collector (I replaced 16 with no help), 0TR4 ends up 17 volts at the base but shuts off?

As the problem only lasts 1 to 3 seconds it's hard to get measurements. My volt meter is too slow to get a full reading so I  use my scope to check and I'm lucky it has a memory to look at.

The other thing I have noticed during this is at the base of 1TR15 during normal operation it looks like a high frequency oscillation and when the problem hits it goes away.

What gets me is that with 17 volts at the base of 0TR4 it should be turned on but the solenoid shuts off like it"s turned off!

I have checked all ground connections and found 1 bad one for the optics in the tone arm but no help there.

Any help is greatly appreciated.

Jim.

sonavor
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sonavor replied on Tue, Dec 27 2016 11:51 PM

Normally I would offer to hook up a working Beogram and check my voltages for something to compare yours to... but I am afraid I won't be able to do that for a few weeks as I am swamped with projects I am currently in the middle of. If you can post a diagram of the circuit you are measuring and monitoring it might help someone on the forum come up with some other things to try.

-sonavor

joeyboygolf
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Regarding random lifting of the tonearm, I had this exact problem on a Beogram 6000 Quad.

I suspect that the rubber band that drives the threaded bar is loose. (Servo motor drive belt)

I suggest that you invest in a replacement belt set from Dillen.

Regarding the set down position, this is adjusted by moving the ruler slightly, using the adjustment screws in the oval holes.

Regards Graham

Jim Carr
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Sonovar, I will scan a copy of the circuit to upload when I go back to work on Tuesday.

Graham, When I am testing the platter is off and the tone arm is down but just sitting in space so the servo motor is not running. Also the set down issue is fixed.

Thanks, Jim.

Jim Carr
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Here is a schematic for the circuit. The components are 1TR 14, 15, 16 & 0TR 4. Any help is greatly appreciated.

Thanks, Jim.

Jim Carr
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Sonavor, I have been back at my 4002 and this is what has happened. First it has sat for a couple of weeks to get some other things done. I put it on the bench set up my scope and hit on. The tonearm went over, set down and almost immediately picked up and set down! It happened so fast I did not get a single measurement. I turned on the scope's save function and of course it would not do it again the rest of the day.

I think it is a ground problem as the voltage all around TR 16 goes so high as if it is shorted. I have replaced it but no luck. I have jumped the board ground to the power supply caps but it still did it. Now I have a jumper from the bottom of R57off the emitter of TR 16 to see what happens.

I have never had a semiconductor have a intermittent problem  like this they have always been bad or good. But you never know. I just wish it would break so I can find it!!!!

One other question. I have never seen a resistor like the one for the emitter of 0TR 4. The one that gets switched into the circuit when the tonearm goes down. It has 2 leads on each end and one from each end are soldered together. Do you know what this is about?

Thanks, Jim

sonavor
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Jim Carr:

One other question. I have never seen a resistor like the one for the emitter of 0TR 4. The one that gets switched into the circuit when the tonearm goes down. It has 2 leads on each end and one from each end are soldered together. Do you know what this is about?

There is a description of that for the Beogram 4000 on my Beogram 400x thread. I haven't ever done any measurements on a 4002 regarding this functionality because I haven't had any problems there yet. However, the functionality should be pretty similar. What happens is the solenoid is instructed to activate with full power applied. Within several milliseconds of that event, the load resistor is switched in to reduce the current through the solenoid. It should end up at a value that is enough to hold the solenoid (in the tonearm down state) but not draw as much current as when it first engages. Maybe there is a problem with that switch. See if you can take a picture or two of the switch.

-sonavor

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