Sign in   |  Join   |  Help

Beogram 4000 malfunction after shipment

rated by 0 users
Answered (Not Verified) This post has 0 verified answers | 65 Replies | 2 Followers

T4000
Not Ranked
Gothenburg, Sweden
27 Posts
OFFLINE
Silver Member
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.

 

All Replies

sonavor
Top 50 Contributor
Texas, United States
3,533 Posts
OFFLINE
Gold Member
sonavor replied on Sun, Jan 10 2021 12:31 AM

Hi Per,

I connected up the Beogram 4000 turntable I have in my workshop to an oscilloscope and took some measurements of key signals involved with the servo motor. I looked at six signals:  FF, /Q0, FR, /Q2, the forward servo motor node and the reverse servo motor node.

My oscilloscope can measure four signals at a time so I divided my measurements up.
I exercised the Beogram while looking at the four control signals (FF, /Q0, FR, /Q2) and while looking at the motor nodes plus two control signals (/Q0, /Q2).

Here is my test setup.
I opened the Beogram and removed the platter.
Then I soldered on some test leads to the six nodes I wanted to measure. I connected a clip from the probe grounds to the Beogram gound.

 

Now to look at the measurements.

-sonavor

 

sonavor
Top 50 Contributor
Texas, United States
3,533 Posts
OFFLINE
Gold Member
sonavor replied on Sun, Jan 10 2021 12:40 AM

The first Beogram 4000 servo signal measurement is of the "ON" event.

Here are the four control signals during "ON"

Here is the "ON" event showing what is going on with the servo motor nodes

 

Here are the motor signals for the "OFF" event

Next I will show the fast and slow scanning events.

 

 

 

sonavor
Top 50 Contributor
Texas, United States
3,533 Posts
OFFLINE
Gold Member
sonavor replied on Sun, Jan 10 2021 12:49 AM

On the Beogram 4000 servo motor during forward/reverse scanning here are what the control signals are doing.

 

 

 

 

sonavor
Top 50 Contributor
Texas, United States
3,533 Posts
OFFLINE
Gold Member

Here are the servo motor nodes during tonearm scanning.

 


sonavor
Top 50 Contributor
Texas, United States
3,533 Posts
OFFLINE
Gold Member

Hi Per,

Those Beogram 4000 waveform measurements for the servo motor are from a properly working Beogram.

From what you have described on your BG4000 and shown from your oscilloscope, I believe your issue is still what a control signal.
You always get a reverse servo motor command.  Even when you manually advance your tonearm, then plug the Beogram in (if I remember correctly).

On my BG4000, I can advance the tonearm out to the middle of a record, unplug the Beogram...When I plug the Beogram back in it remains off until I press "ON" again.

If we assume that your Beogram 4000 was working perfectly when you bought it then the current problems are due to the shipping damage. Something is out of place related to the BG4000 servo commands.

Otherwise we decide that this Beogram 4000 was faulty to begin with and the problem could be something electrical internally that has to be found and fixed.

The first scenario seems more likely.

My suggestion is to connect the scope to control signals and verify what state they are in for the "ON" event.
I will leave my Beogram 4000 and with the test wires soldered on in case we need to compare some other signals.

-sonavor

T4000
Not Ranked
Gothenburg, Sweden
27 Posts
OFFLINE
Silver Member
T4000 replied on Mon, Jan 18 2021 4:59 PM

Hi sonavor,

I tried to configure the oscilloscope the same way you did, and here are the results during Error #5*

Config at first pic (same voltage range as your oscilloscope)

Ch1: FF
CH2: /Q0
CH3: /Q2
CH4: FR

 

 

Config at second pic (slightly different voltage range to fit the image better)

CH1: Motor Forward
CH2: /Q0
CH3: /Q2
CH4: Motor Reverse

 

I hope my input make scene.

/Per

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

sonavor
Top 50 Contributor
Texas, United States
3,533 Posts
OFFLINE
Gold Member

Hi Per,

On your Beogram 4000 "ON" event you can see that your FF control signal only lasts for about 200msec before it stops and the FR control signal takes over. We know that the "FF" signal begins with your pressing of the ON button. The "FR" signal on the other hand is not coming from your actions so something else is causing that.

We need to investigate where that is coming from. 
I think I would take apart the button panel where the leaf contacts are. Remove the contacts enough where you can see that the contacts are making contact and not making contact.  The same exercise might need to be done with the rest of the control switch mechanisms.
In that mode you would have to manually engage the contacts for the various control signals. 

It may sound extreme but you don't want to keep looking at the result of the problem. It will take some digging to find the root of the problem.

-sonavor

T4000
Not Ranked
Gothenburg, Sweden
27 Posts
OFFLINE
Silver Member
T4000 replied on Mon, Jan 18 2021 8:42 PM

Hi sonavor,

I did check the leaf contacts in the control panel before.

Nov 25: "Tonight, I opened up the control panel to measure the button switches. They are all according to spec. I paid extra attention to >> and OFF, but no remarks".

After that I have also cleaned the leaf contacts according to Beolover's instructions. The leaf contact functions were confirmed with buzzer. 

Shall I redo these tests? Or is there anything else I can check?

Per

 

sonavor
Top 50 Contributor
Texas, United States
3,533 Posts
OFFLINE
Gold Member

Hi Per,

Yes, you checked them with a DMM, right?  That doesn't mean there isn't something going on with them during operation of the control panel switches and sensor switches.

The commands to the motor are coming in from the control areas of the Beogram.

We need to know what signal or signals are causing the problem. Right now all we have been able to do is look at the result (affected) side of something not working correctly.  The fault does point to being something involved in reverse movement of the servo motor so I would at least isolate the switching for that control logic. However, I would open up all of the switches where I had to manually do everything to check switching connections for sure. I'm not saying you have to do it that way. That would just be my method. The goal is to find the signal(s) that are not correct in the ON event.

-sonavor

T4000
Not Ranked
Gothenburg, Sweden
27 Posts
OFFLINE
Silver Member
T4000 replied on Tue, Jan 19 2021 2:53 PM

Hi sonavor,

Bingo!Thumbs Up

So, I first noticed that the error (#5, listed below) disappeared when I opened up the control panel. Same as last time (a month ago, if you recall). I now measured all switches again (at the wire pins). First with the oscilloscope, where I found a strange result at FR. As it should be grounded per default, I tried to short FR to ground. Then the error disappeared. Checked the switch with DMM, and it intermittently rests on the ground knob/pin. Not always. What bugs me the most is that I carefully tested this switch last time, and at the time, it was all OK. I will now try to clean the FR pin again, then I hope this error is gone for good. 

Now the question is what to focus on next. The counterweight issue, I will look into soon. It's not stopping the function right now, but I know I have to fix it.   

Current error status:

  • Error #1: Tone arm lowering even if no record is present. (Permanent error)
  • Error #2: Slide reaching end position, but servo motor continues to push the Slide to the center. (Intermittent error)
  • Error #3: Slide stops at 12" position, then slowly moving towards the center, then returning back home. Occurs with and without record. (Permanent error)
  • Error #4: When playing a record, the arm lowers, but after 1s the servomotor starts and the arm scratch across the record for about 0.5-1cm. (Have not been able to play any records in a very long time, so I don't know about this error)
  • Error #5: At ON, Slide moves ~1 cm to the left, then returning home again (Error hopefully resolved).

Per

sonavor
Top 50 Contributor
Texas, United States
3,533 Posts
OFFLINE
Gold Member

Hi Per,

That is great news. A DMM continuity check is a useful tool but with the leaf type switch contacts in the Beogram 4000 sometimes you just have to open it up. If you look at the Beolover Blog Rudy often completely removes all of those types of switches, straightens them and applies gold plating. I haven't gold plated mine yet but when I restored mine (a number of years ago) I did straighten them and cleaned them. Once they are restored they work good again. I haven't had to mess with mine since the restoration. I actually like that the switches are like that as you can always repair them.

The tonearm counter-weight and tracking force adjustment just take patience while getting the parts in the right configuration.
Use the photos I posted as a guide to the general placement of the counter-weight. Then recalibrate the tracking force dial to get the correct setting.
The most important thing is that the tonearm has uninhibited travel vertically in the range that the stylus will be tracking a record.
For the tracking force gear with the spring and the adjustment knob, I like to calibrate it to the 1 gram mark as that is the area I use the most (1 gram to 1.2 grams).

Your servo motor errors are likely related to the tonearm not being setup correctly with the counter-weight and with the position of the tracking sensor assembly (at the base of the tonearm). So getting the counter-weight and tracking force solved will help with the remaining problems.

After the counter-weight issue you can start looking at the tracking sensor.

-sonavor

T4000
Not Ranked
Gothenburg, Sweden
27 Posts
OFFLINE
Silver Member
T4000 replied on Tue, Jan 19 2021 7:55 PM

Hi sonavor,

The counterweight is now adjusted so it is well free moving vertically (similar distance as on your Beogram 4000), and the tracking force knob is re-calibrated. The B&O tracking force gauge was used to set the weight to 1,5g (MMC 5000).

Per

 

sonavor
Top 50 Contributor
Texas, United States
3,533 Posts
OFFLINE
Gold Member
sonavor replied on Tue, Jan 19 2021 11:32 PM

Hi Per,

You are making good progress now.

I think the next step is to remove the platter and then start the Beogram (ON button).  The arm should travel forward to the first set down position.
Let it drop then it should just stay there...no advancement of the arm.

If that is not the case and the tracking sensor instructs the arm to move forward you will need to make an initial adjustment of the tracking sensor to control that. It doesn't need to be adjusted perfectly at this point but you don't want it advancing on its own.

With that under control you can put the platter back on and check the tonearm lowering limit position per the service manual. I believe you already checked the distance between the top of the platter and the fixed arm, right?

-sonavor

T4000
Not Ranked
Gothenburg, Sweden
27 Posts
OFFLINE
Silver Member
T4000 replied on Wed, Jan 20 2021 8:27 AM

Hi sonavor,

Yes, the progress is good now. Feels good as well.

The lowering limit position is adjusted since before. The tone arm is lowering, but it doesn't stay there. The tracking sensor is pushing it inwards, so it should be adjusted. Any advice how to adjust it?

Thanks.

Per

chartz
Top 25 Contributor
Burgundy, France
3,976 Posts
OFFLINE
Gold Member
chartz replied on Wed, Jan 20 2021 2:58 PM

It's a bit of a trial-and-error adjustment of the shutter diaphragm collar. You will get it right, eventually.

See chapter 4.6.

Jacques

Page 4 of 5 (66 items) < Previous 1 2 3 4 5 Next > | RSS
Beoworld Security Certificate

SSL