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This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
A test I have been anxious to try is the platter motor output signal. My first Beogram 4000 wasn't able to produce a nice, undistorted sine wave up to 6 VRMS for 33 RPM and 45 RPM. That first Beogram 4000 turntable has been performing nicely for me but I have been really wanting to know the state of this second turntable.
I am pleased to report that this unit easily produces a beautiful sine wave to drive the platter motor above 6 VRMS for both 33 RPM and 45 RPM. This picture shows the 33 RPM signal. I actually dialed the voltage down to just over 6 VRMS. There is room for it to go higher. The service manual calls for a maximum of 6.5 VRMS and a frequency of 42.3 Hz for the 33 RPM speed. I am at 42.69 Hz but I still have other adjustments to make.
The motor amplifier output at 45 RPM speed selection will also go over 6 VRMS without distortion. It's frequency is a little higher than the service manual as well though. The manual asks for 57.3 Hz and I am measuring 57.96 Hz.
The next step is to start buttoning down the Beogram so I can do the rest of the adjustments and get it to the point I can really evaluate the performance of the new cartridge mount from Beolover. I am hoping to reach that step sometime this weekend.
I believe I have the platter motor amplifier adjusted to a good starting point now. First I set the control panel speed trimmers to the center position of the trim pots.
Then I adjusted the main board speed trimmers 1VR1 (33 RPM) & 1VR2 (45 RPM) so the motor output (with the appropriate speed selected) frequencies were as close to 42.3 Hz (33 RPM) and 57.3 Hz (45 RPM) as I could get them. Once that was done I readjusted the motor amplifier output signal so it was between 6 VRMS and 6.5 VRMS for both speeds.
The output looks pretty good as measured on my oscilloscope. I will have to recheck the speeds when I get the platter and belt on.
Here is the 45 RPM speed output
Thanks John upping my learning vurve
Collecting Vintage B&O is not a hobby, its a lifestyle.
Hi John,
Awesome thread!! I scanned the 24V bulb circuit diagram and posted it on my blog:
http://beolover.blogspot.com/2016/01/beogram-4000-alternate-circuit-diagram-2.html
Rudy
http://beolover.blogspot.com
http://beolover.com
That's a nice quality scan, thanks!I found this picture of the BG4000 control panel 3IL3 & 3IL4 from my first Beogram 4000 unit. It has a slightly different board than my current one but it also has the two lamps in series so they are 12 V lamps. This second BG4000 turntable has the board that can be wired for either the 12 V or 24 V lamps which is what was confusing. But that is the goal of this 400x thread...to collect and show as much information on these great turntables as possible.
Tonight I installed the replacement tracking sensor lamp source I got from Beolover. It is an LED replacement with a built in trimmer resistor for fine tuning the sensitivity of the tracking sensor. I like this integrated replacement as the original trimmer was added on later and hangs off the tonearm transport assembly. This replacement looks cleaner. It is also a drop in replacement so the original can be restored if I want to later.
Here is the tracking sensor ready to go on the Beogram tonearm assembly.
I did a quick test of the Beogram operation to see what works and doesn't work (although I don't have the platter installed or the tonearm adjustments done yet). The turntable control logic appears to be working. Right now the tonearm transport moves kind of slow but I think that is because I haven't adjusted the tracking sensor or any of the tonearm FO/RE adjustments.
While watching the turntable go through its logic I realized that I haven't done anything to the tonearm transport position switches. They are the same kind of switches that are on the control panel so I need to clean them with a fiberglass brush and apply a little Deoxit conditioner.Here is the assembly with the springs that activate the position switches. It has to be removed first to get to the switches.
The position switch assembly is underneath the sliding actuator assembly I just removed. The power to the tonearm drive motor also comes from this board so it must be desoldered to get to the underside of the board.
Here is the top of the board with the tonearm drive motor wires removed. The switches on the underneath side of the board don't appear to be as tarnished looking as the switches were on the control panel but I will remove and clean them anyway.
After cleaning the switch contacts with the fiberglass brush and treating them with Deoxit Fader lubricant I am happy with the way they look and I'm glad I took this board out for cleaning.
I reassembled the Beogram and exercised the play operation again (still without the platter or phono cartridge). There are still quite a few adjustment procedures to go through.Tomorrow I will balance the tonearm and adjust the phono cartridge position. After that I will work on the tracking sensor adjustment and the forward/reverse speeds.
The work so far has been cleaning and replacing some old parts. To get the Beogram working again a number of adjustments have to be made. There are the mechanical adjustments for the tonearm position detection. That also required the cleaning of those switch contacts. Another crucial adjustment is for the tonearm tracking. The service manual has a specific adjustment procedure to calibrate the way the motor for the tonearm operates as the stylus tracks a record groove.
However, before the tracking adjustment procedure can be done on this Beogram I have to get the tracking to a stable operating mode. The metal aperture plate that directs light from the tracking lamp to the photo detectors was off to one side a bit on this turntable. What happens then is one of the photo resistors gets more light right at the start and the tonearm motor tries to compensate. So what is necessary is to zero out the tracking detector so the tonearm motor functions pretty close to normal before going into the specific service manual adjustments.
This process can take a while as I have to first get the aperature plate centered between the Beogram 4000's two photo resistors.
The initial adjustment process takes several iterations to get it right. The goal is to have the aperature plate centered between the two photo resistors and lined up with the light source. The light source will be between the two photo resistor slots by the way the lamp housing cover mates with the photo resistor container. Where the tracking sensor can be out of whack is the position of the aperture plate which is mounted to the tonearm. This picture shows the screw and bracket that mounts the aperture plate to the tonearm. The tonearm base pivots as the stylus travels the grooves of a record. When the tonearm is not moving, the aperture plate should be centered between the two photo resistors.
After getting the tracking sensor all centered I noticed there was a problem with the mechanics of lowering the tonearm. The tonearm was not lowering straight down. There was a slight pull towards the center of the turntable. What that does is cause the tonearm motor tracking sensor to immediately detect some motion and start moving.
The problem here is strictly mechanical with the tonearm balance and lowering adjustments at the rear of the tonearm.This link to my first Beogram 4000 earlier in this thread shows the tonearm adjustment screws at the rear of the tonearm and detector arm assembly.Here is a picture of this current BG4000 after I have the tonearm adjusted to drop straight down. No more skewing of the aperture plate when the tonearm lowers.
Now that the tonearm mechanics are working where the tonearm can lower and raise straight up and down without tripping the tracking sensor I was able to get the sensor adjusted where the Beogram start, stop, forward and reverse operations work without the tonearm motor trying to drive off somewhere by itself.With the tonearm assembly moving pretty good again I needed to readjust the position switches so the detection points are correct. Here is a picture that shows the position switches labeled with their function.
The operation of this Beogram 4000 has a problem with the solenoid for lowering the tonearm not functioning. Unfortunately for me I made a mistake and let a probe slip while trying to check the solenoid voltage. The result was a small spark and a couple of burned out lamps - the detector arm lamp and the 33 RPM indicator lamp. Fortunately I had spare lamps but I think some other circuit components may have got damaged.
I replaced the two lamps and the new ones work. I can see thought that my turntable logic is not working quite right. Prior to the probe mishap this Beogram tonearm transport was travelling correctly and stopping at the 25/30 cm and 17 cm locations. The problem was that the tonearm wouldn't lower. Now the tonearm transport is no longer stopping at the stop points.I will have to trouble-shoot this new problem. As for the solenoid not activating, a closer check of the tonearm transport showed me that the switch for the current limit on the solenoid was not making contact at rest. That would mean the solenoid couldn't get enough power to turn on. The switch is the same type of switch that I cleaned on the control panel and the tonearm position plate.Here is the solenoid current limit switch removed for repair. The contacts should be normally closed. This one has a gap.
Here is the solenoid current limit switch re-installed. The switch now is normally closed like it should be and disengages when the solenoid activates.
The solenoid is ready to work now but I still have the problem with the probe mishap. Something happened to the Beogram logic where it can't detect the stopping points for the record sizes and it can't enable the tonearm to drop. I checked the control panel logic and couldn't tell if a logic signal was incorrect. Tomorrow I will measure all of the key control voltages and compare them to my working Beogram 4000. Hopefully it will reveal the problem area.Here is the Beogram 4000 control panel board I will check the voltages on.
sonavor:Where the tracking sensor can be out of whack is the position of the aperture plate which is mounted to the tonearm. This picture shows the screw and bracket that mounts the aperture plate to the tonearm.
This adjustment bracket construction is my pet peeve on the 400x series. It looks like something you would design at 3:55 pm on a Friday to avoid having to stay and work overtime.
Nice work and great pictures as always!
--mika
John check your PM
tournedos: sonavor:Where the tracking sensor can be out of whack is the position of the aperture plate which is mounted to the tonearm. This picture shows the screw and bracket that mounts the aperture plate to the tonearm. This adjustment bracket construction is my pet peeve on the 400x series. It looks like something you would design at 3:55 pm on a Friday to avoid having to stay and work overtime.
Here is a nicer picture of the replacement tonearm drive pulley from Nick. It looks like it could (should) have been the original pulley.
Tonight I put my Beogram 4000 #1 unit (the working turntable) on my bench so I could compare control signal voltages with the non-functioning turntable. It looks to me like the problem may be in the detector arm circuit on the main board. There is a DR signal that controls a lot of the logic on the control panel board that is stuck low (0.08V) on the bad unit. The good unit has 6V on that signal.
Here is the full list of signals I measured to compare. They might be a handy reference later.
The measurements above are with a DMM and are with the platter off so the detector arm will always think a record is present. That is why the DR signal is a constant 6V (logic high) on the good Beogram 4000. To really see that circuit function correctly I need to measure it with the platter turning without a record to see what the detector arm instructs the logic board. Here is my test setup - my scope probe connected to the DR signal entering the control board from the main board.
The oscilloscope shows that the DR signal resolves to 6.5V when the detector arm isn't detecting the platter ribs (so it thinks there is a record present). When the detector arm detects the platter ribs, it drops DR to a logic low signal (0.08V). That low DR signal prevents the turntable logic from dropping the tonearm. The bad Beogram 4000 unit is stuck with the DR signal always 0.08V so that is a big problem. My guess is the probe mishap yesterday burned out a component or two in the arm detector circuit in the main board. Tomorrow I will start trouble-shooting those components.
The updated Beogram 4000 main board schematic that Beolover recently provided is a nice addition to my trouble-shooting of the detector arm circuit.Here are snippets from the original and new schematic of the detector arm circuit. The new schematic finally shows the 50K trimmer that is mounted on the trace side of the main board. Dillen had explained what that trimmer is for. Now I have the schematic to show it.
The detector arm circuit on the main board is where I suspect a failed part is that is preventing my Beogram tonearm lowering solenoid and position detection sensor logic from working. This detector arm circuit sends a key signal (DR) to the control logic board and the non-functioning Beogram 4000 has that signal stuck low (0.08V). That tells the logic board that there is not record present.I spent some time today to use my oscilloscope to measure each of those points on the schematic where a signal is shown. I measured them on my working Beogram 4000, then checked and compared the measurements from the non-functioning Beogram. Later I may post some pictures of each of those measurements.Fortunately the non-functioning Beogram is getting the signal from the detector arm. It also processes the signal through the first three measurement points (up to the 1VR7 trimmer) before 1TR15. The measurement between the collector of 1TR15 and the base of 1TR16 fails. Instead of a waveform I get a constant 6V. So here is the root of the problem.I checked 1TR15 first and it passed. That leaves 1TR16. It fails -
I continued on and checked the other transistors that go to the +6VDC rail. They were good but if you look at the schematic, 1TR16 is different in that it connects directly to the +6VDC rail where the others have a resistor between them to the rail. My probe mishap blew out two 6V lamps and now I see it also took out a transistor. The components it blew out were all components without a resistor to limit the current through them. Only the 33 RPM (and not the 45 RPM) lamp blew because the Beogram was in 33 RPM mode. The detector arm lamp blew because it is directly connected to the +6VDC rail and finally, 1TR16 is the lone transistor connected to the rail.
I currently have 1TR16 removed from the main board. With it out of there the Beogram of course does not function correctly. Interestingly though, it does now stop at the 30cm LP position and the tonearm lowering solenoid engages. So I believe I am close to having this turntable back where I can start final adjustments. All I need is to find a replacement NPN transistor for 1TR16 (B&O part: 8320095). The service manual says it is a BC239B or BC184BK transistor. I'll have to see if I have a spare or a substitute.
HI
I may need to get the logic circuits checked in my Beogram 4000, are the ares highlighted in green responsible for the solenoid and tone arm lowering function?
thanks
Kevin
The Ǭ₁ signal is generated by logic on the board and controls the tonearm lowering and raising solenoid. There are a number of signals from the tonearm transport buttons and the control panel buttons that factor into that logic. So if Ǭ₁ is not firing (it should go from around six volts to zero volts to lower the arm) when a signal calls for the tonearm to lower, then the solenoid won't react. However, since Ǭ₁ is controlled by several signals you have to check all of them. Start by checking OFF, ES, DS and W0. The first three (OFF, ES and DS) have to be high. Then the W0 signal (normally six volts) briefly goes low, then back high, when the command to lower the arm occurs. That short, low pulse causes Ǭ₁ to go high which, in turn, latches itself in that position until an event happens to raise the arm (ES, raise arm, forward, reverse or off buttons). Currently my tonearm lowering solenoid is firing again but I have other control logic problems involving the tonearm drive motor that I have to trouble-shoot now.Good luck with checking your signals and be careful with the measurement probes. It is best to unplug the Beogram when moving probes. I found out the hard way.
This has been an amazing thing to read and see, I'm truly startled by your dedication to this beogram 4000.
I have done many beogram lids and have made really poor lids look so much better, even getting many scratches out.
The only thing i noted was that the beogram 4000 lid was harder to work on, I have one lid I was going to do some restoration on again
after spending some time on it before, but I want to do some more work on it.
I am also needing to get my Beogram 4000 tested, I've done as much as i can but the solenoid is not engaging.
i suspect it could be the logic circuits but hopefully I will be able to get that checked soon.
Great work
cheers
Thanks Kevin,I have the materials to fix the Beogram dust covers but so far I haven't done one. I need to go ahead and learn the technique. I even have a badly damaged one I can practice on so I don't really have an excuse not to.Tonight I went over my latest problem, the tonearm motor having ceased working. Luckily the problem was minor and typical. A wire had broken off one of the terminals of the main circuit board. It was hard to see and I found it while working back through all of the control signals. The wire is back on now and the tonearm drive motor is working fine again.I think I am down to two electrical problems. There is still an issue with the solenoid on the tonearm lowering. The symptom is when I start the Beogram playing the tonearm correctly moves to the 30cm position and stops. Then there is about a 30 second delay before the solenoid finally engages and lowers. The other problem is the detector arm is not detecting an empty platter. Even though I could see activity on the detection arm circuit on the main board, I think the signal is too weak. I may just need to reposition the detector arm lamp to improve the detection sensitivity. I guess I could also have a failing photo resistor in the arm. To test that theory out I used a powerful LED flashlight to boost the amount of light on the platter when the detector arm was trying to detect a record. That did the trick. When I hit the correct spot the tonearm assembly keeps going until it determines there isn't a record. I was also able to observe it change speeds to 45 RPM at the 17cm spot for the first time.
It looks like one of the two problems is fixed now. I resoldered and repositioned the detector arm lamp and it started correctly detecting the platter ribs. The tonearm travels the entire platter now and returns home when it doesn't detect a record. The final test was to check if it detects a 45 RPM single. It does so the 17cm sensor switch is in the correct position and the detector arm appears to be working fine. The tonearm also lowered but it still has the 30 second delay.