ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
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
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
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
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.
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.
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
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.
On the Beogram 4000 servo motor during forward/reverse scanning here are what the control signals are doing.
Here are the servo motor nodes during tonearm scanning.
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.
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: FFCH2: /Q0CH3: /Q2CH4: FR
Config at second pic (slightly different voltage range to fit the image better)
CH1: Motor ForwardCH2: /Q0CH3: /Q2CH4: 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).
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
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?
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
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:
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.
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).
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?
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.
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
Yes, my method is to re-center the tracking sensor control where it is as close to the ideal position and all of the adjustment screws are at their centered positions (so they have room for adjusting).Here is an old thread of mine on the Beoworld Workbench Forum that shows the components involved. A repost of one of the photos is here (please excuse that I mispelled "diaphragm" in the picture :-) ).I begin these adjustments with the platter removed.A first thing to try is to just see how much out of position the tracking sensor is.You might get lucky and all it needs is a quick adjustment of diaphragm eccentric adjustment screw (B).First loosen the locking screw (C). Then see if you can turn screw (B) such that the arm does not advance by itself when lowered.Screw (B) has limited range so if you rotate it to where it stops (DO NOT OVER TORQUE IT) and the tonearm tracking still advances the arm by itself then you will have to move to a more in depth resetting of the tracking sensor assembly.Hopefully your Beogram only needs a little adjustment of screw (B). Perhaps screw (C) had come loose.
If the quick adjustment of screw (B) could not solve the problem then it is likely that your Beogram shipping incident caused the diaphragm to shift where it mounts onto the tonearm base. That means you will have to reset the diaphragm position on the base first.My method for this case is to loosen the diaphragm height adjustment screw (A). The height of the diaphragm is shown in the service manual but there is also a left and right rotation of the diaphragm that defines where slit in the diaphragm rests over the tracking sensor (inside the black box).In addition to screw (A) I loosen locking screw (C) then rotate the eccentric adjustment screw (B) where it is centered...meaning I can rotate it left or right if I need to later.With those initial adjustments made I slowly and carefully try to adjust the diaphragm by pivoting it until I have the tracking sensitivity almost where it needs to be (per the service manual). Note that pivoting (rotating) the diaphragm means that you also need to be aware that the diaphragm height doesn't get off where it needs to be.So the process is with the Beogram 4000 platter removed, make an adjustment, press the ON button and let the arm move and lower...check to see how sensitive the tracking is. I consider the initial position good when the arm lowers, the arm does not advance on its own but I can get it to move with a light nudge to the side of the tonearm. When that point is reached I gently tighten screw (A) being careful that the diaphram position does not change as I tighten the screw.Now the tracking should be at the starting position I like it to be for the final tracking adjustment as spelled out in the service manual.That is where you put the platter back on the Beogram but do not install the platter belt.You are going to rotate the platter by hand.A record is placed on the platter (the service manual calls for a B&O test record that I have never been able to find).The Beogram is turned on and you scan the tonearm forward to the middle area of the record.When the arm lowers onto the record it will just sit in the selected groove. Manually rotate the platter and observe how many revolutions of the platter before the Beogram servo motor begins to advance the arm. It should being within two revolutions then advance the arm every revolution after that.If the servo does not advance then this is where you begin to use the diaphragm eccentric adjustment screw (B) to fine tune tracking sensitivity.Screw (B) has a limited range of adjustment left and right. That is why it is important to have screw (B) in a centered starting position so you have room to make the fine adjustment. Once the tracking sensitivity is correct you gently tighten the adjustment locking screw (C). Later you can apply a dab of removable glue to screw (C) so it can't easily come loose. However, I recommend you not do that until you have tested record playing on the Beogram for a while.As on the other adjustments, be patient and take your time.-sonavor
I posted a description of how to make the adjustment but that post went to moderation for some reason.
This post was made while the previous post was in moderation.The previous post is out of moderation now :-)
That adjustment is a weak point of the design - a bit Heath Robinson!
Hi sonavor, Jacques and Heath Robinson,
The adjustment of the Diaphragm is now done. Screw A was needed. I would assume that fixed both error #3 and #4, right?
That would give the updated error status:
Yes, it should. Error 1 is either due to any of the following:- Fixed arm lamp is burned out- Fixed arm sensor is not transmitting a good signal. This could be due to the position of the fixed arm lamp not being positioned correctly.- Problem with the circuitry that supports the fixed arm sensor.I would suspect the lamp or positioning of the lamp as the most likely sources of the problem. Especially when you said your problems occurred after the shipping incident. Error 2 sounds like the end stop switch not always making good contact.After Jacques' comments I had to go order a couple of books of Heath Robinson's works. Pretty humorous.
sonavor: After Jacques' comments I had to go order a couple of books of Heath Robinson's works. Pretty humorous.
After Jacques' comments I had to go order a couple of books of Heath Robinson's works. Pretty humorous.
Yes indeed, great drawings.
Sometimes great ideas start as funny sketches.