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
As before, I adjusted the platter motor amplifier output (1VR3) while monitoring the sine wave on an oscilloscope. This picture shows the scope probe attachment point.
The platter motor turns fine and with the tonearm chassis moving, I see a maximum of around 0.5A on the 24VDC rail. The 6VDC rail pulls around 0.15A.I adjusted the platter motor amplifier output where the sine wave just started to distort its shape for 33 RPM. This still happens prior to getting to 6V. It actually starts distorting at around 4.6VRMS. Here is a picture of the scope when 33 RPM is selected.
Switching speeds to 45 RPM, the sine wave distorts some more. The platter motor still spins but I cannot get the nice sine wave above 4V.
The results are a definite improvement over the amplifier output I was seeing with the original, malfunctioning transformer. I still need to find out why I can't get a clean sine wave up to 6 VRMS on the platter motor amplifier as the service manual calls out.
As for transformer news, the transformer shop in Michigan doesn't have a form factor small enough to build me a replacement that will fit inside the Beogram 4000 chassis. So I started looking at toroidal transformers as they come in smaller sizes for the same amount of output. I believe I found a supplier in Maryland that can build me a toroid transformer that has a 120VAC primary and two secondaries (a 24VAC and a 10VAC). The size will be 2.8 inches in diameter x 1.4 inches high. That will fit into the space available where the original transformer was. The toroid will not have the 1:1 secondary (120VAC) for the strobe lamp. To keep that functionality I will have to wire a diode-resistor-LED circuit to the 10VAC or 24VAC secondary and use that for my platter speed strobe light. I should have the toroid transformer ordered by Monday.
-sonavor
Knowing that my Beogram 4000 is still a long way from being ready for use again, I spent a good part of today looking at the platter motor drive voltages in relation to the different functions. What I discovered was my Beogram was not engaging the tonearm to play in my earlier tests. For some reason, it started working today. The result is I now see the largest current surge when the tonearm solenoid engages. That changes my specifications on what the power requirements are on the 24 VDC rail.
Here is what I see regarding power usage on this Beogram.
At standby, the 24VDC rail shows a draw of 0.05A on my power supply. The 6VDC rail show 0.00A.When I press the ON button the motor starts at 33 RPM and the tonearm carriage moves inward. The current draw for this state is 0.44A on the 24VDC rail and 0.14 on the 6VDC rail. If I pause the tonearm carriage, the 24VDC rail current drops to 0.38A.
When I change speed to 45 RPM, the paused current on the 24VDC rail is at 0.45A and the current with the tonearm carriage moving is 0.51A.
Yesterday, I thought those were my maximum current draws. To my surprise, today when the tonearm engage solenoid started to work (briefly), I saw the current draw on the 24VDC rail jump up to 2.3A during solenoid operation. Once the solenoid completed its travel, the current dropped back down to between 0.4 and 0.5 amps (depending on the speed selected). The raising of the tonearm doesn't cause a rise in the current draw on the 24VDC rail.I don't know if that 2.3A draw is the expected amount for the engaging of the solenoid but it is more than I was going to account for in the new transformer. So I'll have to go back to the engineer with this new information.
The transformer may not have to provide 2.3A, at least not constantly. If the reservoir capacitor iswell proprotioned, it will be able to provide the major part of this very brief current spike without seeing atoo large drop in voltage.
Martin
I checked with the transformer engineer and he said the toroid would be able to handle a 2.3A spike without any problems so I have ordered a prototype to try out. In the meantime, I am going to work on a couple of mechanical problems with the turntable. I noticed that the lever for lowering the tonearm sticks and does not easily return to position. Also, the tonearm drive pulley is not true...it has a slight wobble to it. I will post some pictures later.
That is good news then!
My own Beogram 4000's carriage pulley has a slight wobble to it too, like yours. The pulley itself is very sturdy and true, it is the grub screw on one side only that causes it in my opinion. The pulley is a bit loose on the worm screw, it has too much play.
Martin contemplated to re-manufacture it to better standards a few years ago. But he has so many projects!
I tried that myself, but machining the central hole is difficult, because of its keyhole shape. Now perhaps 3D printing would make it possible.
Jacques
chartz: My own Beogram 4000's carriage pulley has a slight wobble to it too, like yours. The pulley itself is very sturdy and true, it is the grub screw on one side only that causes it in my opinion. The pulley is a bit loose on the worm screw, it has too much play. Martin contemplated to re-manufacture it to better standards a few years ago. But he has so many projects! I tried that myself, but machining the central hole is difficult, because of its keyhole shape. Now perhaps 3D printing would make it possible.
Speaking of Rudy, I watched his video on the Beogram 4002 again where he took apart the solenoid mechanism. He mentioned one of those levers sticking and it sounded very similar to my lever problem.
In order to access the lever, the fixed, detector arm assembly had to be removed.
I carefully worked the lever off the axle to clean it and apply new lubricant.
Re-installing the lever means carefully placing back the spring and snap ring on the axle.
Last, the wire spring that rocks the lever back into locking position when the solenoid releases to raise the tonearm.The lever works smoothly again now. Before, the wire spring could not budge the lever.
Removing the tonearm control lever for service means re-mounting the fixed arm to the chassis. That means running through all of the service manual adjustments for the arm positions. The first thing in mounting the fixed arm was to make sure it is at 90 degrees to the shiny rails the arm assembly travels. This took me a few tries. After that, I had to make sure the tonearm was positioned correctly relative to the fixed arm. This also took a number of adjustments. I finally got the arms adjusted where I think they are correct. The tonearm is an equal distance from the fixed arm all the way from rear to front when the tonearm lowering lever is centered in the V of the tonearm bracket ("D" in the service manual).
I think I have the arm assemblies adjusted to a good position now but the adjustment procedure on page 4-5 of the service manual is a little confusing to me. The note in the text of the adjustment procedure mentions "If the arm D is to be tilted". Arm D, per the picture, doesn't tilt but it can adjust left or right via the mounting slots. It is necessary to adjust arm D after adjusting the fixed arm position. On the fixed arm position, besides adjusting for 90 degrees to the rails, I had some problems trying to achieve the 1.2mm gap between the tonearm lowering lever and the damping cylinder arm. The arm in the service manual looks more straight up and down next to the damper cylinder. Mine has more of an angle. There isn't enough play in the fixed arm assembly mounts to move the fixed arm forward more (towards the damper cylinder).
The problem I had on my adjustment was the arm D section with the V slot was too close to the adjustment screw for the tonearm depth. The tonearm couldn't tilt forward without the arm D bracket bumping into the fixed arm assembly. I spent a while getting the fixed arm 90 degrees to the rails and as far forward (to try and achieve the 1.2mm gap with the damper cylinder rod). I finally had to add some spacers on the arm D mounting screws to provide some relief on the area where arm D enters the fixed arm area. This current adjustment allows the solenoid to move the damper, free up the tonearm to lower while maintaining parallelism between the two arms.
chartz:My own Beogram 4000's carriage pulley has a slight wobble to it too, like yours. The pulley itself is very sturdy and true, it is the grub screw on one side only that causes it in my opinion. The pulley is a bit loose on the worm screw, it has too much play.
Here is the tangential drive pulley out of this Beogram 4000. The condition it arrived in was with some cracks in the pulley mount. This obviously contributed to wobble. The cracks are probably due to age and wear from operation. The similar pulleys (except in black plastic) of the 4002 and 4004 turntables also show signs of hairline cracks. This reminds me of the Beocord 800x - 9000 clutch assembly that almost always have cracks (or beginning cracks) in the stress points.
I applied some epoxy to the plastic mounts with the cracks so hopefully that will prevent the set screw from causing any further separation. However, on the Beogram 4000 pulley, you can see from this picture that the pulley will not turn true. The green arrows show the epoxy and the nylon washer I installed (the original felt washer was missing).
Nick have some very nice repro BG4000 pulleys in alu. I can highly recommend them!
Dillen: Nick have some very nice repro BG4000 pulleys in alu. I can highly recommend them! Martin
That is excellent news! I have sent you a PM for Nick's contact information.ThanksJohn
I want one too!
Good news on this project - the new transformer and custom pulley for the tangential drive have been ordered. It will probably be a couple weeks before the transformer arrives so I'll take a break and look at some other projects while I'm waiting.
As for me, I'm just waiting for my new pulley!
You are located closer to the source so you should get yours first. Let me know how it works when you do.
I will!
Hi!
This is Nick's pulley. Fits and works perfectly, with the original felt washer
No more wobble, and Nick even supplies an Allen key!
The belt is Martin's.
That is so awesome! I can't wait until mine arrives. I'll have to ask Nick if he has the pulleys for the Beogram 4002 drive screws as well. They are almost the same except that the hole for the shaft is a little different. My Beogram 4000 was missing the felt washer so I was using a nylon one instead. I suppose I could make my own out of a piece of felt.
Yes he has the 4002 ones too
Thats a good looking pulley, I like the look of aluminium.
Collecting Vintage B&O is not a hobby, its a lifestyle.
I received notification today that my toroid transformer is built and was shipped out to me today. It should arrive early next week so I hope to be working on the Beogram power again soon. I'll post some pictures once it arrives.
Today I received the new drive pulley from Nick. It looks great. Thanks for making these pulleys Nick.Here are some side by side comparisons with the original pulley. I plan to get it installed and tested with the Beogram this weekend.
The new transformer arrived today and I did a quick fit check. I'll have to re-route my power cable a little but it appears to fit fine.
Cant wait to see the result, and the costs
So far so good. After switching power inputs back to the bridge rectifiers and connected to the new transformer, the Beogram's tonearm motor, lights (except the strobe), relays, solenoid and platter motor all operate from the turntable control panel.
The next step is to drill the mounting hole for the toroid transformer and finish bolting it down. The Beogram platter motor amplifier still is not up to spec as I figured would be the case. With the external DC supply I could see the amplifier output improved over the original, defective transformer. This new transformer also results in a better motor output - around 5 VRMS on 33 RPM and around 4.7 VRMS on 45 RPM. The service manual expects 6 VRMS. I get 6 VRMS on my Beogram 4002 Type 5503 turntable AC platter motor.So there are still a lot of work to do on this turntable before it is ready to play records again.
I was able to get back to the Beogram 4000 this weekend. The first thing I did was drill and tap the hole to permanently mount the toroid to the Beogram chassis. After that, I decided to connect a couple of red wires to the transformer primaries (at the same points as where the transform connects to the fuse box. I connected those red wires to the Beogram strobe lamp circuit in an attempt to retain the original strobe lamp design.Here is a picture of the mounted toroid and strobe wiring.
Here is a picture of the Beogram strobe lamp. I measure 115 VAC across the lamp terminals when the Beogram platter motor is turning but the lamp doesn't illuminate. Jacques has been gracious enough to supply me with a spare lamp so I will repost a picture later with, hopefully, a working strobe.
Here is a picture of the power supply circuits all buttoned up and ready to use. The next step is to start on Beogram suspension, platter and tonearm adjustments.
John, your envelope is ready to leave home first thing tomorrow morning. Are you sure its relay contacts are good? I can't remember whether you have tested it separately or not. I have a 27k resistor in series with mine.