Hi sonavor,

Today I finally had some time to look at the logic circuits described in Service Manual, section 3-1, Diagram 1. I focused on the ES and OFF signals. Those signals feed into the NAND gates in 3IC0, 3IC1 and 3IC2. After pressing ON, I measured as follows:

• 3IC0, Pin 10 (ES in): 2,6V
• 3IC0, Pin 11 (OFF in): 2,6V
• 3IC0, Pin 1 (NAND out): 0V

• 3IC1, Pin 10 (OFF in): 2,6V
• 3IC1, Pin 11 (ES in): 2,6V
• 3IC1, Pin 1 (NAND out): 5,6V

• 3IC2, Pin 3 (OFF in): 2,6V
• 3IC2, Pin 4 (ES in): 2,6V
• 3IC2, Pin 8 (NAND out): 0V

Is looks like 3IC1 is defective.

What does the jury say?

Per

On those NAND logic devices it only takes one input to be a logic "0" in order for the output to be a logic "1".
3IC1, Pin 1 has a 1.2KOhm pullup to +6V so it appears to me that one of its inputs must be a logic "0".  So 5.6V would be reasonable for the output.

Those NAND logic devices do not fail very often and should it turn out you do have a failed NAND device it would bring into question whether you Beogram was a working unit prior to shipping. It seems unlikely the shipping event would have damaged a none moving part like that.

While strange things are possible I think it is more likely that your fault is in something that sends voltage signals to the logic controls.
The question to check is what should 3IC1, Pin 1 be when you press "On".
According to the Beogram 4000 Design Notes I pointed you to 3IC1 is the logic for the tonearm Lift so I don't believe it is a problem here.

Check the 3IC0 logic device and the flow diagram in section 5-4 of the service manual.
According to the Design Notes, 3IC0: Automatic Slide Transport In, is the logic device that starts the Beogram. Monitor the SI signal that starts things off. 

-sonavor

This diagram shows the logic board and which logic gates relate to what Beogram 4000 functions.

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Hi sonavor,

Regarding the logics:

I have now read the document you recommended, BG4000 Training Notes manual. I will leave 3IC1 be for now. I focused on section 3-25 (3IC0). I measured the voltage of pins, but I'm a bit hesitant to draw any conclusions anymore, so I'll just present the results below. As you also pointed out the Fault-finding diagram 5-4 in the Service Manual, I'll present the measurements for these signals as well.  

IC0

Pin                     Function           Voltage (V)                                                                                

1/2                     NAND (/Q0)       0.06                          

5                         SI                        5.85                          

7                         +6V                    5.85                          

8/9                     NAND                5.75                          

10                      ES                       1.93                           (a bit lower this time, 2.6V last time I measured)

11                      OFF                    1.93                           (a bit lower this time, 2.6V last time I measured)

12                      /Q1                    5.57                          

13                      Input fr.3IC9      2.32      

IC1

Pin                     Function           Voltage (V)                                                                                

5                         WO                    5.8                          

13                      "Is SI missing"    0.77            

IC7                                                                          

Pin                     Function           Voltage (V)                                                                                

2                         DR                      5.87                          

5                         BL                       5.88                          

The detector arm light = On                                                        

Regarding SI:

I studied the Start Impulse (section 3-11 in the Training Notes manual). I don't have an oscilloscope at hand, so I'm not quite sure I can observe the 10ms pulse we are talking about here. I can buy one if needed. Can transistor 1TR20, that generates the SI, give some hints? Any ideas what to look for in that case?

Regarding what happened during transport:

As far as I was told, the Beogram was in good shape prior shipment. Please note though: issue #5 was not present when I received the Beogram. That error appeared a couple of days later. The "only" failures the first week after arrival was issue #1 -> #4:

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 (and scratches) the record for about 0.5-1cm.

I'll try to describe (and remember) exactly what was going on when #5 first appeared:

I was moving the Slide from Position [ D ], first groove of the record, slowly to the right pressing ">" with several, short intervals. (Purpose: to get the stylus over the aluminum plate for tone arm weight check). I pressed ">" a few times, and then the issue #5 appeared, causing the Beogram to switch off. After that I removed the Slide Contact Spring assembly to reach the Slide Contacts. I pressed the contact pins, probably from the right to the left, and then I might have smelled burned electronics.

Per

Just looking at your IC0 logic -

IC0

Pin                     Function           Voltage (V)                                                                                

1/2                     NAND (/Q0)       0.06                          

5                         SI                        5.85                          

7                         +6V                    5.85                          

8/9                     NAND                5.75                          

10                      ES                       1.93                           (a bit lower this time, 2.6V last time I measured)

11                      OFF                    1.93                           (a bit lower this time, 2.6V last time I measured)

12                      /Q1                    5.57                          

13                      Input fr.3IC9      2.32     

If my memory serves me correctly...
Your Beogram 4000 appears to be in the "On" state according to the IC0 flip-flop pins 1 & 2 state.
The IC0 flip-flop circuit is latched where /Q0 is a logic "0" (or "L"). 
Maybe someone else who has gone through this recently can confirm.
So it appears that your IC0 logic is saying the Beogram is on and can move the arm transport forward. 

Since that isn't occurring then something else must be stopping the tangential arm assembly.

When you are in this state do you see the platter motor pulley turning? Can you feel the tangential arm assembly motor turning (or trying to turn?).
You mentioned that the spindle and spindle pulley had come off earlier.
In re-assembling that are you sure the spindle is correctly positioned now?
See if you can manually turn the pulley and move the tangential arm assembly with the servo belt removed. Is it easy to move or do you feel a lot of resistance?

-sonavor

I decided to go over the Beogram 4000 control circuit to refresh my memory.
The logic "Low" ("0") on the  /Q0 signal that comes from the 3IC0 flip-flop circuit, will turn on 1TR25 to drive the tangential arm assembly (the slide assembly) forward. The same control over 1TR25 occurs with the "FF" control panel button is pressed.

So mechanically, check the spindle movement that drives the slide and make sure it moves correctly. As I mentioned earlier, you can test it manually by disconnecting the servo pulley belt and turning it by hand.

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

-sonavor

Hi sonavor,

Today when I started up the Beogram, Error #5 was gone. I decided to screw the spring assembly back in place, but then Error 5 reappear. And disappear. Error #2 and #3 could be reproduced when #5 was gone (caught #3 on tape: link). And I might have a new issue. Error 6, the tone arm seems to be stiff, it doesn't lower (this stiffness can also be seen in the Error #3 video). And then.... Error 7, I broke this plastic construction:

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The below text was written before the Beogram (and I) went all erratic (I never got to measure 1TR25, let me know if it still makes sense):

There is nothing mechanically stopping the Slide. I can however not electrically run it forward due to error #5. When I remove the servo belt and manually turn the pulley it runs smoothly. The manually turn the pulley is what I have been doing so far to move the Slide for the various tests/adjustments.
The Slide servo motor is running when the Slide is returning home. The Slide moves back home at ON. If it is already at home, it moves 0.5cm to the left, then back home and turns off. Error #5.

Platter motor is running.

My logic circuit measurements in previous posts were made with the servo belt removed, otherwise I would not have time to measure before it tuns off again. So, my measurements are under that condition; Slide moving back home (I stop the condition by manually pressing SO).

Regarding the spindle
The Slide Spindle seems move as intended, and I also confirmed the alignment seems to be according to Service Manual 4-6 "Adjustment of Spindle". See also video the Spindle when Slide is returning home: link

New observation:

This PCBA seems bent (red) and the conductor (blue) seems to be damaged. I think I read something about this (blue) being normal when the trim pot was installed, though.

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Per

Hi Per,

It is a little confusing regarding the exact status of the Beogram 4000.
If I read your post correctly you are saying the "Error #5" (where the Beogram won't start) is now intermittent, right.
Regarding your video of the Beogram 4000 starting, stopping at the first set down point, then continuing on to the end stop....
That looks normal to me. The tonearm will not actually drop if there is no cartridge mounted. It requires some weight to go with the arm balancing to drop freely.
When the Beogram continued forward to the end stop did you click FF to cause that to happen or did it do that on its own?

-sonavor

Hi,

That makes us 2.

Error #5 is now intermittent, yes. Sadly.

The tone arm is not balancing anymore, it is stiff, regarless of solenoid position (error #6). Somethign might have happened when I reinstalled the cover a few days ago. 

In the Video I only pressed ON, the rest was done by the danes.

Per

Okay, then what must be happening with the Beogram travel across is the result of the tangential tracking sensor being out of alignment.
That would make sense based on the Beogram components that were out of place when you received the Beogram shipment.
What is happening there is most likely the Beogram sensors are telling it that the arm is free and should be playing a record.
The tangential arm sensor thinks the arm is not in the correct tracking position so it instructs the servo motor to advance it forward to catch up.
It never catches up because the sensor is out of alignment so it just continues forward until it hits the end stop.
We don't need to mess with that just yet but will obviously have to come back to it soon.
The good thing is that a portion of the tangential arm control logic appears to be working fine :-).

For the stuck tonearm you need to carefully observe the tonearm movement mechanics.
If the arm does not freely move when the arm lowering lever allows it to drop then there has to be some physical thing blocking it.
First try it with the Beogram unplugged.
Manually move the lever that the solenoid would engage to release the arm lowering damper and watch the arm lowering lever action.
Checkout how the lever is engaging and disengaging with the horizontal bar that releases the tonearm itself.
Is there contact?
Is the arm lowering damper working?
Make sure the arm lowering limiting screw isn't preventing the lowering.
Did someone move the tonearm counterweight too close to the tonearm base so it won't pivot down?
Like I said, there has to be something mechanical there causing a problem and the mechanical components are all right there at the back of the tonearm.

-sonavor