Beogram 4000: A New Pulley, Hood Bumpers and Shipping Back to Italy

The Beolover always strives to improve his craft and get things as perfect as possible. So I realized that I was not fully done yet with the restoration of the Beogram 4000 from Italy. My recent efforts to restore a Beogram 8000 from Japan introduced me to the concept of rubber hood bumpers that soften the impact if the hood is closed. It makes quite a big difference in terms of how it feels to close the hood. The sound when the hood seats on the enclosure is just so much more solid when the bumpers are present. Unfortunately they all seem gone at this point in time, and that is the reason that it took me some time to realize that all the classic B&O decks actually have(had) them! All that is usually left are some small holes filled with black degraded rubber remnant. This shows how it looked on the hood of the Beogram 4000:

It is easy to get the black stuff out with a 2 mm drill bit operated by hand (do NOT put it on a Dremel or similar...it is easy to damage the plexiglass):

Like with the Beogram 8000, rubber O-ring segments work well to restore the bumpers. In the case of this 4000, however, I needed to use 2mm diameter metric ones since the 0.1" type I used on the Beogram was too thick to squeeze into the holes. I glued the segments in with a bit of contact glue on the tip of the segment. Then I used my 3D printed cutoff template that I developed for the Beogram 8000 and razorblades the excess length off:

A perfect-length bumper resulted:

It has the right length to right the hood into a horizontal alignment with the plinth. The way the hinges are designed at the back of the hood, a ~1mm gap should be around the entire perimeter between hood and plinth if the hood is to be perfectly horizontal. These bumpers guarantee that. Beautiful!

Beyond this issue I also was a bit annoyed that the carriage ran a bit noisily when returning to the home position after a record was played to the end or OFF pressed. This was the result of a somewhat wobbly pulley, a result of a crack in its set screw assembly:

I exchanged it with a custom manufactured Aluminum pulley provided by Nick (via www.beoworld.org):

This fixed the issue and also looks beautiful. I think I will make this a standard part of my restorations since most pulleys are (or will be soon) cracked and/or run wobbly. This pulley quieted the mechanism down quite a bit and made it much more pleasant to use this Beogram 4000!

After these two tasks it was finally time to send it off. My customer requested state-of-the-art Beolover double boxing, and so I used this occasion to make a short video about the proccess:

May the Force (and gentle FedEx men&women) be with you on your way to Italy!

Beogram 4000: End Groove Detection Issue

After polishing the hood I thought I was done with this Beogram 4000, but not so. A last full performance check before boxing it up revealed a strange fault when ON was pressed with no record on the platter. The carriage would properly travel inwards in search of a record, but then before hitting the end switch ES the carriage would suddenly stop. Only pressing FF would release it from this state. However, then after letting the FF key go the carriage would immediately travel back without even touching the ES. In a healthy state the carriage should travel until the ES is activated and then it should return to the home position.

A closer look revealed that the carriage stopped right when it closed the MV switch that enables the end groove detection mechanism. Here is the relevant section of the circuit diagram:

Here is how it works: Whenever the MV switch is activated by the slide, MV' and MV are connected in the diagram. This puts part of the voltage on the motor across BE of TR24. So whenever the motor revs a bit higher, such as when the needle enters the end groove, the transistors 24/23/22 are activated and DS finally goes LOW. This tells the control system that it is time to lift the arm and drive the carriage home. Now this mechanism is of course only useful when the needle is on the record and entering the end groove. When the arm is up and the carriage is driven forward or backward this mechanism needs to be disabled. This is achieved via D4 which feeds the collector of TR25 into the base of TR23. 

The collector can only be high if FF is activated either by pressing the key or via Q0' which is LOW whenever the carriage is driven towards the center of the record after pressing ON. The tracking mechanism does not use TR25 since it directly goes into TR27/28, i.e. end groove detection is not disabled if the carriage tracks normally.

Further tests of the matter revealed that Q0' remained LOW even as the carriage stopped. This told me that the control system was still of the opinion that the carriage should move, hence the fault needed to be on the executive side of the system, i.e. right here in the MV circuit. I measured D4 from the back of the installed main PCB and promptly saw that it was open circuit, which killed the deactivation mechanism, and the end groove detection mechanism was active even with the arm up. After turing the board around I saw that the diode was cracked in half:

The original OA90 diode is a Germanium diode, but can easily be replaced with a modern 1N4148 Si signal diode since its only function is to block any voltage from the MV circuit to apply to the collector of TR25. Here is a picture of the 4148 installed:

After this I replaced the board and gave the deck a test drive. All good again. Listening to Walt Dickerson's "To My Queen" while I write this, which is definitely one of my all time jazz favorites. O.k. maybe now it is time to finally send this 4000 back to its owner.

Beogram 4000: Polishing the Hood and a Strange Hinge Pin

I am giving the Beogram 4000 that I restored recently the final touches. The last item to check off on the list is always polishing the hood. Like most Beograms that I saw so far this one also had a badly scratched up hood from carelessly stapling things on top of it while it sat in 'storage'. This unit had a couple more items that needed to be taken car of: One of the hinge pins was not original. At some point the short press-fit pin must have 'vanished' (one really wonders why someone would take it out...but such is the human creativity...;-), and a replacement pin was installed. The 4 mm replacement pin fit well into the hinge parts, but was too long and so it stuck out a bit:

Here a picture from the bottom of the hinge assembly:

I took the pin out and cut it by 4 mm with a jig saw and a metal blade. That allowed the pin to be inserted a bit deeper and it looks original now:

On the other side of the hood the aluminum trim had come off from the plexiglass:

I fixed that by applying a strip of double sided tape and pressing the strip back to the hood body. I recommend to not use epoxy or similar glue for this since the aluminum strip covers the screws that hold the hood to the hinge, and if the hood ever needs to be take off the trim needs to be pried off.

Anyway, after these tasks I set out to polish the hood. this one was special since it also had some issues on the inside, which is much more difficult to fix since it is hard to polish the inside. Luckily the damage was fairly small and most of it appears to have been tape residue:

I was able to remove it with a bit of detergent and a Mr. Clean Magic Eraser Pad. After that it needed a bit of buffing with polishing fluid, and that seems to have done the trick. There are a few more small very localized dings on the inside, but I chose to let them be since it is almost impossible to to a full sanding/polishing job on the inside since one cannot get to the corners.

Then I focused on the main job, the outside of the hood. Here are a couple impressions of the degree of scratching:

Nothing too special, but the depth of the damages required to start out with 200 grit sand paper to level the surface with the deepest damages:

This was followed with 320 grit:

and 400 grit, the first wet-sanding step:

It starts getting clearer already, but a full treatment with Micro-Mesh is required to get back to a fully translucent state:

And finally after buffing it with polishing fluid:

all good in the hood department now! A few more days of testing and this Beogram 4000 is ready for its journey back to Italy!

Beogram 4000: Adjusting the Tracking Force and Replacing the Strange Original Front Center Cabinet Guiding Washer

The Beogram 4000 that I just finished up is now running smoothly. I am playing 'Song for My Father' by Horace Silver (unfortunately a reissue, since the original first pressings are unaffordable these days...sigh!!), which is one of my favorite jazz tunes while writing this post.

Before I got here, however, I still had to do a bit of work on this Beogram: Adjusting the tone arm weight and limits. I also replace the strange standard guiding washer that is typically found installed in the front center guiding slot to ensure a straight movement of the plinth when it is pushed back to secure the aluminum panels. Here is a picture of the original washer including the shoulder bolt:

This awkward setup just does not work well, and consequently later Beogram 400x have a much better design based on an eccentric washer shape. I recently designed 3D printed replicas of this design since they often crack in 4002 and 4004 models that are outfitted with plastic versions of it. See this video for their installation. The parts are available via my Shapeways store (five washers are needed to replace all of them).

Here is a picture of the new washer installed together with a new M3 bolt (note the much lower profile of the assembly, which is beneficial when installing the aluminum panels as chafing is avoided):

After this small detail, I did the arm adjustment. Most important are the zero weight and tracking force calibration and the proper adjustment of the arm lowering limit, which can be the final stop gap that keeps the platter from ripping the needle out of the MMC cartridge in case of a failing photosensor or misadjusted sensor bulb. Earlier I posted videos about these two procedures (tracking force calibration, arm lowering limit). Equally important is the improvement of the weight adjustment screw assembly, which I usually upgrade with a M3 nut and washer. This allows to permanently fix the adjustment in place, which is critical for a successful out-of-the-box setup when I send the turntable back to Italy. The original setup with the locking washer is too flimsy, which can result in a change of the calibration during shipment. Here is a picture of the installed nut:

And here the needle on the tracking force gauge at 1g after adjusting everything:

Ah...Horace Silver via a perfectly adjusted 4000 and my Beomaster 6000 4-Channel - perfect pairings!...I am in Beoheaven..;-)

Beogram 4000: Installation of a New Gold Coated DIN5 Plug and a Grounding Switch

The beautification of the Beogram 4000 that I am restoring right now continues. I installed a grounding switch and a new gold plated Neutrik DIN5 plug. The grounding switch allows to combine signal and system grounds of the Beogram. This essentially allows to switch between the grounding scheme of the later 4004 models and the 4000/4002 set-up where system and signal ground are separated. Depending on the amplifier set-up it can be beneficial to be able to select either one to avoid the formation of ground loops that can cause humming. I recently made a post that illuminates this in more detail.

This shows the switch installed. The shown orientation corresponds to the original 4000 set-up with separated grounds. Flipping it to the left would connect both grounds:

Here are a few pictures of the DIN5 replacement. This shows the corroded original plug:

And here is a picture of the new plug:

Beautiful! this shows the leads as connected on the inside:

Good to know that the precious MMC signals can now travel unimpeded!

Beogram 4000: Adjusting the Chassis Springs and the Platter Height

The Beogram 4000 that I am rebuilding right now is entering the 'beautification phase'. It works now very well, and what is left are the exterior and a new good plated plug etc...So I set out to adjust the platter height and tilt and the leaf springs that hold the floating chassis of the turntable. This task is a relatively complex one since one has to "try[] to hit a bullet with a smaller bullet whilst wearing a blindfold, riding a horse" (to say it with Scotty in the 2009 Star Trek reboot...;-). Since sensor arm orientation relative to the floating chassis, platter tilt angle relative to the chassis, linear travel in the opened transport lock and belt tension all play significant roles in the adjustment process, one needs some patience and may have to redo things a few times until one hits the sweet spot where the platter is centered and leveled with the aluminum panels and parallel to the arms, and the chassis does not touch the locks when they are open.

I recently made a couple of videos that show the basic approach. They are posted here. Here are a few pictures of the fully adjusted platter relative to the aluminum panels:

And an 'in-action' detail. She is getting real pretty now!..;-): 

The aluminum panels were quite dirty on this unit. Here is an area in comparison before and after cleaning with Mr. Clean Magic Eraser pads and some (hand-) dishwashing detergent:

Before:

And after:

What would we do without Mr. Clean??!!

Beogram 4000: Exchanging the Electrolytic Capacitors, the RPM Relay, and Adjusting the Motor Signal

I marched on with the restoration of the Beogram 4000 that is on my bench right now. After replacing the reservoir and motor capacitors, I went ahead and replaced all electrolytic caps on the main and power supply board with Japanese made 105C grade long lasting units. I also exchanged the RPM relay, since I recently extracted several dead or inconsistent relays of this type from Beogram 4000 and 4002 units. This made me think that these relays should be part of any 'full' restoration to ensure long-term stability. My goal is to get these elegant vintage beauties to a new-like performance and reliability. These pictures show the main PCB in its original state. This is the solder side. There is one Tantalum capacitor in the top left corner that was added post-PCB-design. Even the Danish masters go through a learning curve, I guess...;-):

Here is the component side:

And a detail shot of the RPM relay:

This is a picture of the relay component that I recently developed. It uses a modern encapsulated SMD relay that is broken out with a small PCB that fits precisely to the pinout of the original relay. Hence it can be plugged straight into the original solder pads and no external wiring is necessary. Plug'n Play!

This assembly is available to other enthusiasts. Just send me an email if you are interested.

This shows the PCB after replacing the capacitors and the relay:

This shows the replaced sole cap on the solder side:

On to the power supply board. It has only two Tantalum caps on it (the red dots):

And here with new ones:

After replacing the boards and testing that everything was working properly, I adjusted the motor signal. The AC motor is run by an on-board Wien bridge oscillator whose feedback needs to be adjusted for the right oscillation frequency for 33 and 45 RPM. There is also a potentiometer that controls the amplitude that goes into the power amplifier that finally drives the motor. I recently made  some more detailed posts (link 1, link 2) about the adjustment procedure. Here is a picture that shows how to apply the probes for the measurement:

One needs to be careful to select the right end of the phase capacitor to get the correct amplitude as prescribed in the manual for 33 RPM (6V). Here are the oscilloscope shots after I adjusted the trimmers to spec. This is the 33 RPM trace

and here is the one for 45 (it will usually be a bit lower than 6V and there is no way to independently adjust it - this is analog technology!..;-):

Beautifully clean traces in this unit! Absolutely lovely! This is Beolove!

Beogram 4000: Installation of New Reservoir and Motor Phase Capacitors Using a 3D Printed Adapter

It was time to replace the big capacitors in the Beogram 4000 that I am rebuilding right now. I always enjoy this procedure, especially due to the clean install enabled by my 3D printed adapter. It accommodates smaller modern capacitor units, while giving the entire set-up an organized look. I made an earlier post that shows in detail what leads are connected where, in case you get confused while doing this procedure...there are a quite a few jumpers to re-solder...;-).

Here is a picture of my capacitor kit with adapter (this is available to other enthusiasts - just send me an email). The two back-to-back caps on the left replace the original bipolar AC motor phase capacitor. The adapter has notches that fit to the original capacitor mounting strap holding everything firmly in place:

I used this kit to replace this fairly messy original set-up:

This is how it looks now after installation:

And here a detail picture of the connections:

On to recapping the PCBs and adjusting the motor trimmers.