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Beogram 4000 malfunction after shipment

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T4000
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T4000 posted on Fri, Nov 20 2020 6:02 PM

Hi!

I have a Beogram 4000 that was damaged in shipment. It was well maintained prior shipment. I initially posted here: https://forum.beoworld.org/forums/t/44481.aspx, but got recommended by sonavor to start a thread here instead.
The [numbers] refers to the Service manual. More pictures and clips can be added upon request.

Mechanical issues found (but now corrected):

a)       The Slide was loose and tilted and the Detection arm was relocated towards the Tone arm (see picture IMG_3629.JPG). 

b)      Pulley [124] came loose during transport and has likely been rattling around freely inside the Beogram. (in this Beogram replaced by a metal version, see picture IMG_3630.JPG). It was found again under the Turntable [4]. The loose Pulley resulted in the free moving Slide.

c)       The Slide threaded rod (Spindle [224]) was hanging loose-ish, also an effect of the loose Pulley.

d)      One of the Slide Contact pins and its plastic holder (Switch E, SO - Switch off/Home position) were knocked off.

Functional issues found (please note that issue #5 is now permanent and overrules the other 4 issues):

1.       Tone arm lowering even if no record is present. Intermittent problem. Happened both on 7" and 12" position. The detector arm bulb is lit up, but something is wrong in the sensor circuits.

2.       Another intermittent problem: sometimes the detection arm function works when scanning an empty platter, but then when the Slide are reaching end position, the servo motor continues to push the Slide to the center. OFF has to be pressed to return.

3.       The Slide stopped over the 12" position, then slowly moving towards the center, then returning back home. This occurred both with and without record. Don't know if this is a normal operation, but it happens intermittently.

4.       When playing a record, the arm lowers, but after 1s the servomotor starts and the arm moves across the record for about 0.5-1cm (my poor Pink Floyd album).

5.       After that I started (in pure frustration) to adjust mechanical bits and pieces according to the service manual. When I came to the step of Tracking force adjustment, I started ON, then pressed Reverse (>) to move the tone arm away from the platter. When I did this, the Slide decided to return to home position. I pressed ON again to repeat the procedure, but the Slide moved ~1 cm, then returning home again (see https://youtu.be/HG-VJ3dCZc0). https I tried a couple of times, but always the same. Also tried to manually push the Slide Contacts, but no reaction. I might have smelled burned electronics, probably for the main PCBA, but I'm not sure on this. The main PCBA [PC 8009012] were inspected visually, no remarks.

Initially I could really need some advice on issue #5, as the other issues can not be reproduced as long as #5 occurs.

Thanks a lot in advance.

 

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T4000
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T4000 replied on Sun, Dec 13 2020 1:23 PM

sonavor:
Did someone move the tonearm counterweight too close to the tonearm base so it won't pivot down?

 

Hi sovanor,

Me and my Beogram needed a break from each other. Now, I'm back.

The tonearm counterweight was the issue. Someone (me) adjusted it a while ago to obtain zero force adjustment ('Static balance' according to the Service manual and Beolover's video https://youtu.be/j3KNUQIsTG4). The result at the time was good, but I must have been reckless lately, because now I noticed that the tonearm base was too close to the counterweight. It's adjusted and moves freely again.

What would you recommend me to look at next?

Per

 

Normal 0 21 false false false SV X-NONE X-NONE

sonavor
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Hi Per,

So that was the source of the stuck arm problem, right?
Now that is resolved.

You will have to post a reassessment of what is not working at this point so reorganize and see what the next step is.

-sonavor

T4000
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T4000 replied on Sun, Dec 13 2020 4:56 PM

Hi sonavor,

Correct. Perfect balance is unfortunately very close to whenthe tonearm base is too close to the counterweight. Slightest move of the adjustment screw, and the arm is stuck. Anyway...

Well, current status is that error #5 is back again.

Same as in my very first post here, I was about to adjust the tracking force using the tracking force gauge. I pressed ON, tone arm moved to 30cm position, and lower. Then I used > to move the tonearm back for the adjustment. It was possible to start moving it back, but not stopping it. When pressing forward (>), it just stopped for a split second, end then continue back home. And after that Error #5 seems to be permanent again.

In Dec 1 you suggested Electrically, measure the DC voltages around 1TR25 and see what they are when the  /Q0 is a logic "0".

So now I did:

C: Varies each time I press ON. I got 16V, 2V, 10V, 5V, 1.3V.

B: 0.6-0.7V

E: 0V

 

Per

sonavor
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Hi Per,

It is curious that this error comes and goes. That makes me think there is something mechanical, something moving that causes the problem. I am also thinking about the fact that the turntable supposedly was in working condition and something during shipping caused the failure. We will eventually figure it out. You might have to dig into the Beogram button control panel.

When you press ON and the Beogram starts you should see a constant voltage on the collector of 1TR25 that would be instructing the servo motor to drive forward until the first set down point. It still sounds like there is a signal telling the Beogram that it is supposed to be turning off or telling it to be in fast reverse mode.  I believe you said that when you manually move the tonearm where it would be over the platter and then turn power on that the Beogram immediately returns the arm to the stopped/home position.  It would be interesting to monitor the collector voltages of both 1TR25 and 1TR34 at the same time with an oscilloscope. 

Regarding the tonearm balance though. The counterweight should not interfere with any movement of course. 
A couple of questions about your adjustment.
Were you making the zero balance adjustment with the tracking force knob set to zero? 
Were you making the zero balance adjustment with a phono cartridge attached?

A cartridge has to be mounted on the tonearm and the knob with the spring tension for the tracking force needs to be down at zero when starting the adjustment.

The result should be a balanced arm that has freedom of movement within the range that the Beogram would be playing a record. Horizontally and vertically.

-sonavor

Keith
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I may be barking up the wrong tree, but I noticed on the last  picture (marked in red) where the PCBA board is lifted, would it be possible for the diaphragm be out of adjustment and forcing the tone arm to run backwards, as it was made to do on the 4000?

Keith.

sonavor
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Hi Keith,

From what has been described about the failure it doesn't sound to me like a problem with the tracking sensor diaphragm. I say that because the problem happens before the tonearm lowering event occurs. The signal from the tracking sensor shouldn't be a factor at that point. 

If it is somehow related then there is also a problem with the Beogram logic not knowing what mode it is in.

I still suspect the problem is related to one of the items that came loose during shipment of the Beogram.

-sonavor

T4000
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T4000 replied on Wed, Jan 6 2021 4:51 PM

Hi sonavor and Keith,

Happy new year! And thanks for your interest in my Beogram! I'm very grateful for this, I can tell you. I hope the below information can give you some clues. Please let me know =)

I manage to borrow an oscilloscope today. Collector of 1TR25 is on Channel 1, and 1TR34 on Channel 2. The short minus voltage at the end of each reading is when home position is reached and the relay shuts the Dane off. 1TR25 seems to be active when the Slide moves to the left, and 1TR34 when the Slide moves to the right.

  • Here are 3 images when pressing ON, with Slide in home position, aka Error #5 (The channels together in first image, and 2 images with each channel separated):

  • Here are two images when pressing ON, but with the Slide firstly manually moved over to the outer edge of the platter before starting.
    (First image with same oscilloscope settings as above, as reference. Second image with Channel 1 zoomed in a bit, in case the initial spike is of any interest):

Regarding the tonearm balance:

Were you making the zero balance adjustment with the tracking force knob set to zero? -Yes, I did.
Were you making the zero balance adjustment with a phono cartridge attached? -Yes, and without the protection.

After adjustment the arm is again free-moving. Just very close. See picture:

 

Regarding the tracking sensor diaphragm.

Would it be possible that error #3 and #4 is related to it?

All the best,

Per

 

sonavor
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Hi Per,

I am afraid it has been too long away from this problem that I can't remember the problems by their number. Please restate the problem when referring to it so it is in context with each post. Otherwise it is too much back and forth looking up what the numbers go with in the thread. It is probably easy for you to remember but many of us are working on multiple projects.  Thanks.

I would like to see the activity on the transistor base leads.  In addition it would be good to use both of your oscilloscope probes to look at the forward and reverse signals on the motor itself...nodes where the emitters of 1TR28 & 1TR29 connect along with the nodes of 1TR31 & 1TR30.
If you see signals trying to drive the motor to reverse and stop then you need to track down what is driving those control signals. 

On your tonearm and counter weight. The weight assembly is away too close to the back of the tonearm. It has hardly any room to move.

-sonavor

sonavor
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Here is what my Beogram 4000 tonearm counter weight looks like from the side. It is balanced and calibrated so the tracking force knob is at 1 gram with the mark shows that it is at 1.

 


T4000
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T4000 replied on Thu, Jan 7 2021 4:54 PM

Hi sonavor,

OK, I'll include the error descriptions in each post from now on.

  • Base of 1TR25 is on Channel 1, and 1TR34 on Channel 2 during Error #5*:

  • Emitter of 1TR28/1TR29 on Channel 1. Emitter of 1TR30/1TR31 on Channel 2. All during Error #5*:

 

Tonearm counter weight

I don't know what I will do with that information.  

 

Per

* Error #5: At ON, Slide moves ~1 cm to the left, then returning home again (https://youtu.be/HG-VJ3dCZc0).

 

sonavor
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Hi Per,

Thanks for the new screen shots. 
Your voltage level readings look a little high.  Make sure the scope probe setting (1X or 10X) matches what the corresponding level is on the oscilloscope setting for the probe channel.  They should both be set the same (either both 1X or both 10X).  That will give you a correct voltage reading on the scope.

From what you show though...I believe they confirm that when you press On that the forward motor command is there but then it goes away as a control signal in the Beogram is sending a command to reverse.

My workbench is pretty full up right now but I will try to sneak my Beogram 4000 and show the same measurements to compare to.


Regarding the counter weight, it is out of adjustment.
Did you perform the balance with a cartridge mounted?  If not, you need to.
Try it again with the cartridge mounted.

-sonavor

 

T4000
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T4000 replied on Thu, Jan 7 2021 6:48 PM

Hi sonavor,

I saw now that the probe for Ch2 had accitently slided from 10x to 1x (the scope is still set to 10x). Do you want me to measure again?

Regarding the tonearm balance:

"Were you making the zero balance adjustment with the tracking force knob set to zero?" -Yes, I did.
"Were you making the zero balance adjustment with a phono cartridge attached?" -Yes, and without the protection.

Per

 

sonavor
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Hi Per,

No need to remeasure the voltages again just yet. Wait until I measure and post mine.

On the tonearm then...it appears the calibration is out of adjustment.
One thing to keep in mind is that there are physical limits to the range that the counter weight can be placed.
Obviously the Beogram originally came from the factory perfectly adjusted so the position you have it at is not correct.

Back it off so the Beogram tonearm can operate correctly.
To re-balance it you will have to do some recalibrating of the tracking force knob. 
It uses a spring to increase/decrease the force as the knob is turned.
There is a tiny set screw at the top of the knob assembly that locks its position.
Loosen that screw so you can reset the starting position of the tracking force knob.
Without any force on the knob you should be able to adjust the counter weight to a good position.
After that you can readjust the tracking force knob to where it indicates the force correctly.
I do that by holding the amount of force dialed in with one hand and putting on the dial knob with the other...then tightening the set screw and measure the resulting force. Be extremely careful to not over torque the screw (any screw for that matter).

It can take several iterations of adjusting everything to obtain a good result. Quite tedious sometimes.
For that reason I typically try adjusting for a tracking force of 1 gram during this procedure rather than zero. That is because I normally use 1 gram to 1.2 grams for my tracking force setting.

I hope that helps.

-sonavor

T4000
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T4000 replied on Thu, Jan 7 2021 9:39 PM

Hi sonavor,

OK, thanks. Then I'll await your measurements.

Regarding the tonearm, are there any pictures online for this adjustment? I can not recall I've seen it on Beolover.

Per

sonavor
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Yeah, I don't believe we have shown that procedure on the Beolover Blog before. Probably because it requires both hands and is so tedious. It also isn't a procedure that you should commonly have to do. Sometimes though, as in your case, the mechanics seem to have gotten too far out of adjustment.

Here is a photo I made a while back that shows all of the components relative to the tonearm balancing.

Normally the tracking force knob setting is fine and the counter weight is only slightly out of adjustment.
As I noted before, there is limited room for adjustment of the counter weight.
Too close in and the tonearm cannot pivot up an down.
Too far out and bracket that connects to the arm lowering lever will not work correctly.

With the tracking force knob removed as shown in the photo there should be no force at all since the spring loaded gear that applies the force is unloaded.
You can start at that point and zero balance the arm. That should result in a good setting of the counter weight.
Then you can attach the adjustment knob, set it to 1 gram and see what you read.
That is where you can get into a few iterations of setting the position of the knob. 
If you cannot get 1 gram set with the adjustment knob then you will have to make a small movement of the counter weight.


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