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

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

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

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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).

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

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

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.

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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

Hi sonavor,

Bingo!👍

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

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

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

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

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

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.