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This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
Hello All,
I'm fixing up a BG4002 (type 5514) and trying to adjust the tracking mechanism.
The available adjustment seems to be a little bit crude, frankly, to the extent that once you think you've got somewhere, when you tighten up the set screw, it goes off again.
I note that Rudy with his very tidy LED alternative adds a trimming pot to adjust the light source for fine tuning after you have got the basic adjustment.
My question is would this sort of set up work with the standard 24v 40mA (?) incandescent bulb? Say a 250 ohm 500mW single turn trimmer?
Or would this introduce unintended consequences?
Regards,
Hi,
The Beogram 4000 had a 100 ohm trimmer as part of its tracking adjustment to help fine tune the tracking sensor. I haven't seen that on any of the 4002 models I have come across. Yes, Beolover has a nice direct replacement tracking sensor light source that also has a fine tuning trimmer. I have done 400x restorations using the Beolover replacement as well as restorations using a new incandescent lamp. You should be able to get successful results either way. It sounds like your mechanical part of the sensor assembly is off a bit. Try to get back to a neutral point where the arm won't drift on its own (it should just stay still when lowered and no force trying to move it towards the record center). From there you can restart the adjustment to get the tracking motor to do its thing after however many LP rotations. It can be tricky to get adjusted though. Check that the adjustment screw has room to move in either direction to adjust the aperture position. You don't want to start the adjustment with the screw already at its limit. Have you already replaced your lamp with a new one? Martin should be able to source you a replacement lamp if you want to go that route.
-sonavor
Hi Sonavor,
Many thanks for your reply.
I had a look through the BG4000 service manual but couldn't see the trimmer to which you refer - until I looked at the service notes. It recommends adding a 100 ohm trimmer to adjust the sensitivity of the servo system, though the bulb it controls (0IL1) is 6v 30mA rather than 24v.
I take on board all your comments about correct adjustment (and I do have a new bulb from Martin on its way) but I can't help wondering if this simple and reversible fix - for which there is a precedent - would make life easier.
In the case of my machine, the diaphragm arm where it is clamped has been mangled somewhat by a previous enthusiast. Is it possible to remove it without demounting the entire arm turret?
Krolroger
Can you post some pictures of your 4002 tracking sensor assembly? Especially the problem area.
Thanks,sonavor
This shows the slightly mangled diaphragm arm. It would be nice to straighten it out but I can (probably) get the adjustment right with it as it is if I fiddle around for long enough. That's why I was looking at the bulb trimmer idea to get it spot on.
And one more:
It was probably kept in a damp shed, judging by the rust.
Yikes, it certainly was. I think a lot of these vintage audio restorations are on equipment that has been stored away in less than ideal conditions. Definitely not temperature controlled.I would take off those rusty leaf springs, treat them and repaint them.
Your picture shows the mount for the tracking aperture missing its mounting screw. Did you have to take that off?To get that set correctly you need to have the screws for the adjustment where they are centered (and be adjusted for either direction) then get the aperture centered and secured to the tonearm mount.
You probably already know this but the tracking adjustment screw moves the lamp and sensor assembly left and right relative to the aperture. The aperture should be centered when the tonearm is not moving where the sensor voltage is balanced. When the tonearm moves with the record groove it moves the aperture so the amount of light changes and the sensor voltage changes. That causes the motor control to signal the motor to turn and catch up. So get that starting position established where the aperture is centered and not moved again. Then just use the tracking adjustment screw to set the tracking sensitivity per the service manual procedure. Note there is another screw on the other side that isn't shown in the picture that locks down the final setting. If the locking screw and/or adjustment screw are damaged then you may have to get a replacement from a donor unit. Also, without the aperture fixed to the tonearm you won't be able to depend on the setting. One reason that aperture mounting screw was there is to be able to raise or lower the aperture in trying to set it as close to the sensor housing as possible (without touching it).
I don't have a 5515 but I have a 5503 and a 5523. This picture is from the 5503. This 5503 looks nice and clean but I can still smell some mildew from when the previous owner had it stored away in some basement.
Hi Sonavor, thanks for your detailed reply.
I've cleaned up the leaf springs and found the initial set for the diaphragm so I'll work with that before fiddling about with a trimmer. Yes, I have the mounting screw.
At risk of going off topic, can you advise me on how to make a horizontal adjustment to the detector arm? Tonearm adjustment is straightforward enough, and lateral adjustment of the detector arm likewise but I'm not sure how to get it horizontal as it seems to be be attached to a single casting. At the moment it dips down by about 2.7mm relative to the end of the tonearm. There is a single securing screw at the end of the arm, but upwards is not a direction this baby wants to travel.
Many thanks,
These Beogram 400x turntables require a lot of patience and careful adjustment. In the end the process creates more of a bond between the owner and the turntable similar to keeping an old, favorite car running.I think the adjustment you are referring to is similar to what I had to do on this page (down towards the end of the page) on a Beogram 4000. There should be a set screw under the rails where they mount to the chassis as shown in a picture on the page referenced in the link.Regards,sonavor
Thank you for the link. Your 400x project thread is an inspiration and a mine of information.
I had fervently hoped to avoid stepping outside my comfort zone which ends somewhere short of floating chassis removal, but maybe it's not so bad if I'm organised.
Why couldn't B&O have made the rails adjustable from on top?
Perhaps smaller running wheels would do the trick...
The adjustments can seem overwhelming if someone has been in there previously and made too many changes (misadjustments). The mind set I always take is I know all of the original parts are there and the factory was able to take those same parts and set up the turntable correctly...so I should be able to get the pieces back together where everything is as they should be. The mechanical adjustments affect each other though so sometimes you do have to reset everything back to a neutral adjusted starting position and begin from there.Regards,sonavor
Well, I'm well off topic now but this is getting interesting.
Chassis came out easily enough. Looking at it, it would seem the easiest way to get the arms/platter relationship correct is with the chassis out to the extent that you can do it without being distracted by other parameters. I've now almost got a consistent 23mm from platter to top of detector arm though running clearances under the sub-platter are a little tight and I don't want to short anything out. Detector arm still dips down a bit though.
I'm reluctant to adjust the running rails except as a last resort because I would introduce a whole set of new variables.
Interesting...I haven't had an opportunity to come across a Type 5514 before. I see that has the heavy platter like the 5501-5503. The platter motor is a DC motor though?
The set screws on the rails of my Beogram 4000 allowed me to adjust the fixed arm 2mm.
Regards,sonavor
Yes, DC motor.
It has the same sub and top platter arrangement as my Type 5524.
Okay, I see now. From the angle the photo is taken it looked like the earlier platter that the Type 550x turntables have.
One more question, if I may.
There is quite a lot of slop in the platter spindle bearing so should one take the 23mm detector arm measurement as if the platter is under slight tension from the drive belt?
I don't take that measurement with any belt tension on the platter. Because the spindle has three adjustment screws for its horizontal position I move the arm over the platter and take three measurments - One nearest the outer edge, one near the spindle center and one towards the back of the platter. When all three points have 23mm then you know you have a perfectly level platter. It usually takes me several iterations of adjustment and measuring to get it set right. It is also another one of those adjustments that you need to make sure your starting point isn't already near the limit of one of the adjustment screws.Regards,sonavor
I'm guessing that the set screws for the rails are as the factory set them - quite a variation from one end to the other relative to the base of the floating chassis - so my instinct is to leave them alone. I don't think the deck has suffered any massive trauma other than misadjustment and years of neglect so I am assuming the rail adjustment is ok.
My latest challenge is to reproduce the 5 cabinet guiding washers, the awful clear plastic ones having disintegrated. Currently making a silicone mould, with a view to making a resin casting or maybe using a low temperature alloy instead as these washers are nearly always missing or unobtainable. Luckily I had a spare set to make a mould from.
Has anyone had a go at this - other than 3d printing? Here's a picture of another use for a hummus pot.
I believe Søren Mexico made some out of aluminum a while back.Regards,sonavor
made these and it worked out good, no need to adjust the trim on mine, but maybe other decks may need adjustable eccentrics, the original square ones gives 4 positions as the center hole is off center
Collecting Vintage B&O is not a hobby, its a lifestyle.
The saga continues.
I wasn't happy with the downward set of the detector arm, so, noting Beolover's tip to flip over the set screws for the tangential carriage rails so they are adjustable from on top, I have done this.
The back rail is easy, but the front rail on my turntable appears to have the bottom of the set screws drilled out or peened so that they are not adjustable or removable.
I suppose therein lies a clue. I will just have to content myself with the available adjustment on the back rail.
Krolroger: The saga continues. I wasn't happy with the downward set of the detector arm, so, noting Beolover's tip to flip over the set screws for the tangential carriage rails so they are adjustable from on top, I have done this. The back rail is easy, but the front rail on my turntable appears to have the bottom of the set screws drilled out or peened so that they are not adjustable or removable. I suppose therein lies a clue. I will just have to content myself with the available adjustment on the back rail.
You are referring to my posting of a Beogram 4002 Type 5513 on the Beolover Blog. I should add that while it makes it easier to work with the rail adjustment that adjustment should be a last resort. If you raise the set screws for the rail height too much then problems crop up for other mechanical adjustments. When these 4002 series turntables do require adjustments like this you just have to prepare for a long ordeal. Sometimes you get lucky but most of the time there is quite a bit of iteration in the adjustments. If things get too far out of adjustment I have to revert to the zero starting position and make very small adjustment steps. I think I went over the adjustments on that Type 5513 Beogram about ten times. It is quite rewarding when it is all complete though so take a break every now and then to recharge. Then keep on keepin' on :).
sonavor
Hi, thanks for reply.
The situation was that my back rails had been adjusted high which I think was contributing to the downward tilt of the detector arm. I know by how much I've wound in the screws in case I have to revert.
With the back rail set screws set high, is the metal plate that fits on top of the rail at an angle? It does make sense that the source of the slope is due to that back rail setting.
Exactly. You can just about see it in the photo I posted in this thread on May 4th.
Getting stuck in again to this project after a short gap.
I thought the following might be of interest when setting the perpendicularity (is that the right word?) of the detector arm.
I assume this needs to track at right angles to the running rail for the carriage, so I made up a perspex jig with scribed lines on it. I used as my datum axis the small holes in the retaining plates for the rear rail and aligned the detector arm to sit at a right angle to the line thus described. This is about 0.5mm misaligned with the right hand edge of the top aluminium deck plate but that's fine.
But the other mechanical adjustments are frustrating and barely repeatable given the amount of slop in the spindle, the tension applied by the belt and the out of trueness of the platter (1.5mm) so have achieved a measurement of between 23mm and 23.5mm in the detector arm height relative to the platter.
I also decided to keep the chassis floating at exactly the mid point between the transit washers when under load (the load being 750g for the sub platter and 750g for the platter - a surprising amount) rather than the 2mm given in the SM, as there is slightly less than 4mm to play with overall.
So far this approach seems to work well enough. I guess in the real world B&O technicians would have regarded the given measurements as something of an aspiration. I wonder what tolerances they would work to?
Very nice! I like it. I have wanted to make one of those jigs myself. Seeing how you have one figured out I sent you an email regarding it.
Krolroger: But the other mechanical adjustments are frustrating and barely repeatable given the amount of slop in the spindle, the tension applied by the belt and the out of trueness of the platter (1.5mm) so have achieved a measurement of between 23mm and 23.5mm in the detector arm height relative to the platter. I also decided to keep the chassis floating at exactly the mid point between the transit washers when under load (the load being 750g for the sub platter and 750g for the platter - a surprising amount) rather than the 2mm given in the SM, as there is slightly less than 4mm to play with overall. So far this approach seems to work well enough. I guess in the real world B&O technicians would have regarded the given measurements as something of an aspiration. I wonder what tolerances they would work to?
Yes. Those adjustments are the most time consuming and can be quite frustrating. All of those various adjustments - platter height, tonearm & fixed arm position, floating chassis leaf spring position and the leaf spring tension all affect each other. It can take a lot of repeated adjustments to get a set of measurements that sometimes are not as exact as you want. The 2mm gap on the transit locks is a measurement I sometimes have to sacrifice. I always make sure there is a gap so that chassis does float but you also want to end up with the platter level with the deck.
I have also found the tolerances in the spindle attachment plate to the sub-platter to get off because the plate welds have become loose. In those cases have had to shim and epoxy that plate so it is perpendicular and rotates perfectly again. Even with the sub-platter rotating perfectly in balance there is still, sometimes, a very small bit of vertical movement in the top platter as it rotates. It isn't noticeable unless you get a flashlight and carefully monitor the deck edge with respect to the rotating platter. I have seen a number of Beogram 400x turntables where everything rotates perfectly straight while other units have a very slight, vertical movement. I guess the top platter was somehow bent during the Beogram's life.