This is a follow up to my recent post about the redesigned Beogram Commander remote control board, which now works in both (DC-motor) Beogr...
Tuesday, March 31, 2015
While I was waiting for the pseudo balanced 'audiophile' RCA cables from Sounds Heavenly, I gave the cabinet of the Beogram 4002 (5513) some TLC. The cabinet was cracked on both corners, and all the guiding washers that hold in place and enable its sliding action were missing. Here is a picture of one of the corners:
It is easy to glue them back together since the cabinet is held together by metal bands. So all one has to do is to put some glue on the wood surfaces and hold it together with carpenter clamps until the glue is dry:
Much more beautiful after glueing the cabinet back together:
This picture already shows one of the new 3D printed guiding washers installed (this one is under the key pad). They enable the cabinet to slide on a precisely defined path (as demonstrated in my YouTube video about the washers). So if you have a 'wiggling' cabinet, then it is time to check if these washers are still there. They were originally made from a flimsy plastic that cracks and degrades over time (B&O realized that soon, and the 4004 models have metal reproductions of them...but the 4002s have usually the (missing) plastic ones. Here is a picture of the replacements. One needs five of them:
Here are the four other locations where I installed them on this Beogram:
Not much left to do except implanting the RCA cables and glueing the two side-tabs of the keypad back down (one can see one of them sticking up a bit on the picture above left of the 'START' label). A Beogram 4002 well on its way to a full recovery!
Wednesday, March 25, 2015
A happy moment in Beolover's lab: Just received a quite pristine copy of a 1976 recording of Herbie Hancock's "Secrets" album (Columbia CA 34280). Almost looks like it was never played. I just love this record. I think my favorite track is "People Music". It has some lovely spaced out sections with awesome 1970s analog synthesizer sounds (apparently on a "Maestro Universal Synthesizer System").
I decided to play this record on the Beogram 4002(5513) that I just rebuilt. It is connected to my Beomaster 6000 4-Channel right now for testing. The Beogram is still apart since I am waiting for a RCA pseudo-balanced cable from Sounds Heavenly to complete the job. This beauty will be used on a McIntosh pre-amp that has RCA inputs. Anyway, here are a couple impressions of my bliss:
Note the nice almost-parallel alignment of the tone arm relative to the sensor arm:
The tracking mechanism rebuild with my latest iteration of the light bulb replacement fixture seems to work great. Everything is very stable. Definitely an improvement over my earlier approach.
Monday, March 23, 2015
I finally got around to get the final 3D printed piece for my Beogram 4002 (5513) remote control system: This part plugs into the 10mm orifice of the remote control receiver board and allows the bolting down of the board using one of the four screws that hold the main PCB in place. Here is a picture of the part (with the screw inserted):
When installed with the remote control board the original screw can be used to bolt it down. The cylindrical feature is just long enough to not force the remote board onto the component pins sticking out from the main PCB of the Beogram, while generating a stable fit of the board. Here is a picture of the part inserted and bolted down:
This concludes my design of the mechanical aspects of the remote system. I am planning to make a couple changes to the firmware of the microcontroller to further streamline the remote operation.
Sunday, March 22, 2015
I appears that Bang & Olufsen manufactured at least two different versions of the Beogram 4002 (5513) model with regard to the power supply. It seems that all of them were designed with a potential upgrade to a CD4 set-up in mind, i.e. the output board that normally only contains the output relay could be exchanged with a board featuring a pre-amplifier and CD4 decoder. As far as I can tell at this point there were two methods to supply the CD4 board with power: One way was to connect it directly via P4 on the main PCB to the 30V power rail. These models only have a simple 4000uF reservoir capacitor.
The Beogram that I am currently rebuilding has it differently: It has a separate supply fed from an additional winding in the main transformer that has its own bridge rectifier and 1000uF capacitor. Here is the pertaining part of the circuit from my annotated Beogram 4002 diagram:
The dashed line indicates the additional CD4 power supply. The unit was outfitted with a special capacitor that combined both the 4000uF main capacitor with the 1000uF CD4 capacitor in one package. Here is a picture of the original unit:
The GND contact for both capacitors is at the bottom of this unit. The contact at the front with the red dot is the 1000uF capacitor, while the second contact (white lead) connects to the 4000uF section of the capacitor. Of course, this type of capacitor is no longer available, which prompted me to replace it with two separate 1000uF and 4700uF capacitors to complete the recap of this Beogram. The question was how to mount them in the single bracket that held the original capacitor. I solved this problem by designing a 3D printed part that would fit into the bracket while housing the two individual capacitors. Here is a picture of the fixture (would you like it in red or blue??):
Here is a picture after installation:
And from the front:
And a detail pic of the wiring:
Of course, I could have abandoned the 1000uF cap and the CD4 power supply altogether since there is probably little chance that this Beogram will ever be upgraded to CD4. But my philosophy is to keep these units original and fully functional, hence I desired to keep everything intact (so that, once time machines are common, we can go shop back in the 1970's and get a CD4 board, and a few nice quadrophonic records...;-).
If you are interested the 3D printed adapter is available including fitting capacitors...just send me an email.
Friday, March 20, 2015
The Beomaster 4002 (5513) that I am currently restoring exhibited the usual issues with the tone arm lift mechanism: The mechanism occasionally failed to lift the arm up in time before the carriage started moving back (scratch & ouch!) to its home position after pressing the 'Stop' button, or at the end of the record. Also, the relay sometimes clicked before the arm was completely lowered. All this pointed towards time-hardened lubricants in the lift mechanism. The cure for this type of behavior is to take the mechanism apart, clean the old lubricants out and re-lubricate it with a suitable grease. I use a silicone grease. This type of grease is well-suited due to its generally non-corrosive behavior, its compatibility with rubber and plastic parts, and its long-term stability.
The restoration process is straight forward, but requires a bit of insight into the mechanism. For this reason I took the opportunity of this restoration to add a short video about the process to my Beogram 400x YouTube playlist. The video also shows how to adjust the arm lowering time to achieve precise coordination with the output relay activation. Here it is:
Wednesday, March 18, 2015
I used my current Beogram 4002 (5513) restoration project as a chance to redesign my earlier approach to replacing the incandescent light bulb in the linear tracking sensor with an LED. In my earlier approach (see here), I reused the bulb housing and just replaced the light bulb part with a 3D printed LED assembly that I had designed as an early (and later abandoned) iteration of my Beomaster 6000 4-Channel incandescent bulb replacement method. While this worked well for the Beogram, it had two significant issues: (1) it was not a drop-in ready solution and required a lot of detail-Dremeling of the original housing to get the glued-in bulb housing separated and replaced, and (2 - probably more important) that the LED position was not very well defined and also not impact/vibration stable. No(2) is clearly an issue when shipping the Beogram, i.e. not suitable for a professional restoration.
So I set out to design a part that is drop-in, 100% mechanically stable, and that is precise enough to only require a small adjustment of the tracking mechanism, which can be done by just turning the executer screw (larger adjustments require a cumbersome realignment of the sensor aperture). The adjustment process is shown in the video below.
Here is a picture of the original bulb housing:
It is interesting to note that the bulb is slightly misaligned, i.e. oriented to one side. I suspect that this reflects 1970's production tolerances, and that most tracking sensor bulb housings will have bulbs at various locations. The obvious consequence is that the installation of a bulb replacement will require the adjustment of the tracking mechanism after installation of the replacement part, independent of the part being an original-style incandescent bulb or a LED replacement.
I designed a part resembling the lower part of the original bulb housing, which is responsible for keeping stray light out of the tracking sensor. Then I combined this part with a custom designed printed circuit board that is responsible for operating the LED.
Here is a picture of the two parts before assembly. The LED is a standard white 0603 SMD LED run with a 2.5 kOhm resistance that it can take the 21V rail of the Beogram. The LED, resistor and the solder points of the leads fit into appropriate cutouts of the housing part:
Here is a picture of the running LED after epoxying the circuit board to the housing. The LED is precisely situated in the middle, i.e. very close to the bulb filament position of the original part:
I updated my earlier video about the tracking sensor light bulb replacement with the new part. It goes through all the steps of replacing the original bulb housing and discusses the tracking sensor mechanism. It also shows how a misaligned sensor behaves, and how to adjust it properly:
Sunday, March 15, 2015
While I am waiting for a 3D print of the redesigned LED light assembly for the tracking sensor of the current Beogram 4002 (5513) I rebuilt the speed indicator scale lights with RGB LEDs. I essentially followed the approach demonstrated in my recent video:
Here are a couple pictures of the actually rebuilt unit:
Original set-up with incandescent bulbs (covers taken off):
And after replacement. There are two resistors since I am using the red and green LEDs of a RGB LED to get a naturally appearing light reflection on the red scale markers. Amber LEDs make an incandescent-like glow, but they do not contain red light, i.e. red scale markers show up gray and even invisible in absence of natural room light - this is discussed in more detail in the above video):
As usual, I further refined my approach a bit: One of the issues with LED replacements of incandescent scale lights is their considerably more narrow radiance pattern. Light bulbs emit fairly uniformly in all directions, while LEDs usually have a narrow emission angle. This is usually combatted by sanding the LED bulb, but some of the directional pattern remains, even after this procedure. In the above video I used tape to shield one end of the scales from too much light, which allowed me to achieve a mostly identical scale appearance as with the original light bulbs. And this worked fine for my personal Beogram 4002, but for a professional 'commercial' restoration I felt this is not a permanent solution, since tape ages and the adhesive can loose its force etc...Since my main interest is to make these beautiful turntables 'future proof' (Imagine Charlton Heston digging it out next to the Statue of Liberty on the beach, cleaning it and plugging it in and the scale lights work...;-),
I needed a more permanent solution. So this time I decided to carefully apply some black acrylic paint to the end of the bulbs and some to the exposed side. Here is a picture of my efforts:
After a few trials slowly adding more painted areas I ended up with this degree of coverage. It is important to also cover a bit of the side wall of the bulb cylinder to absorb some of the photons in that direction to get an even scale illumination.
Thursday, March 12, 2015
I did a quick check on the sensor arm light bulb of the Beogram 4002 (5513) that I am currently restoring. What I found was a pristine bulb, not blackened at all. The bulbs that I so far encountered showed clear signs of filament evaporation, which results in a dark coating on the bulb glass. Not here:
Seems this Beogram saw only little use, or the bulb was replaced at some point. So I will not replace it. It is interesting, however, to note how it sits in its compartment. Absolutely straight on the wires that come in. This suggests that the reason my recent replacement of this bulb with an LED required a high intensity LED may be due to positioning the LED at the wrong location within the housing, i.e. not at the focal point. I will try again with a different set-up. I would enjoy a LED replacement that preserves the original incandescent glow...my high brightness white LED gives it an interesting back-to-the-future feel, but at heart, I really desire to restore these units to their original beauty, just with modern long lasting parts.
I started rebuilding the Beogram 4002 (5513) that recently was sent to me. Today I exchanged all electrolytic capacitors on the PCBs with 105C grade capacitors (I only use capacitors from major Japanese manufacturers such as Nichicon or Rubycon sourced through proven suppliers such as Newark or Mouser). The procedure was uneventful, except for finding a dried spider including web below the PCB, and the realization that there are at least two different solenoid circuits used in the 5513 series.
Here is a picture of the main PCB in its original condition (the spider is in sector B1..;-):
Sector B1 also contains the circuit modification (probably done during a tune-up 'back in the day'):
The PCB before this modification had this configuration of the solenoid circuit:
The modification updates it to
by adding a time delay by splitting the 150k of the original R51 into 47k (1R91) and a different 1R51 at 100k and 1 uF capacitor 1C36. It seems there was some kind of 'spontaneous' arm lifting or lowering that needed to be quenched by inserting this delay (the right side of R51 connects to the 'electronic switch' of the Beogram, i.e. this is one of the two lines that triggers the mechanism). I rebuilt the modification when I inserted the new capacitors:
Here is a shot of the entire PCB after renewal (including the original capacitors):
The only other PCB that has electrolytic capacitors is the output PCB (#8). The 4002/5513 only has one capacitor that needs replacement on this board:
and after replacement:
On to the speed selector bulb replacement!
Saturday, March 7, 2015
The final challenge of my current Beomaster 8000 restoration project was to restore full functionality of the control panel cover. When I received the unit, the aluminum cover had lost its spring action, i.e. it would just loosely sit on top of the control panel by means of gravitational forces. In pristine condition, the panel is held down by the plastic lock which fits into a small cutout in the side of the aluminum panel. When pressing 'programming' on the bar between the cover and the lower body of the receiver, the lock releases the panel and it opens at a measured speed, controlled by a motion damper situated below the control panel to which it connects via a acrylic linkage.
In the present unit, the control panel cover lock was mutilated by Mr. Amateur for a reason only known to himself, i.e. it was not able anymore to hold the cover down. He cut off both ends of the small plastic part. Here is a picture of the sad condition of the lock as I found it:
So, the first step towards restoring the full functionality of the cover mechanism was to reproduce the lock part via 3D printing. For this I extracted a pristine lock from one of my three Beomaster 8000s and took measurements. Then I had it 3D printed on a Stratsys uPrint. Here is a photo of the printed part in comparison with the mutilated original:
This video discusses the process of replacing the lock:
Unfortunately, Mr. Amateur also disabled the spring mechanism of the cover so it would not open up with the mutilated lock not holding it down anymore. To 'achieve' this he removed the metal plate that holds the spring in place in the back of the aluminum cover part, which released the spring and let the cover fall down freely. This is shown here (the wire loop that sticks out needs to be secured within the plastic body of the panel underpinnings to generate the spring force):
Since the original metal plate was lost, I cut a new metal insert from a piece of galvanized steel sheet, and pressed it into the slot. This reactivated the spring mechanism, and the cover would open again by itself when released from the lock:
The next step was to restore the damping mechanism. Mr. Amateur disconnected the linkage from the damper at some point and then must have tried to reconnect it, but he did not understand how to reinsert the lower end of the linkage into the arm of the damper (just put the damper arm vertical, and slide the linkage from the right side over it - the gap fits the protrusion on the arm in that position...live and learn...;-). So he opened the gap in the linkage (apparently by slightly melting the linkage over a flame or similar) in an attempt to stick the linkage back on the arm, but this resulted in a situation where the linkage slipped off the damper arm by itself due to the enlarged gap whenever the cover is closed. I fixed this by exchanging the damaged linkage with a 3D printed replacement, which I designed a few months ago for another Beomaster 8000 restoration where the lower part of the linkage was broken off (see here for a description of this effort). Here is a photo of the 3D printed replacement in comparison with the damaged original:
And here installed on the cover:
The action of the restored control panel cover is shown at the end of the above video. Now this Beomaster 8000 will be tested embedded in my Beosystem 8000 in its fully restored glory for a couple weeks under 'real life conditions' before it goes back to its owner (to make sure that there are no loose ends under the hood - these complex units tend to have intermittent issues, that often only manifest themselves after a using them for a while)
Friday, March 6, 2015
Extensive tests of the Beocord 5000 (4715/4716) that I rebuilt recently (links to the relevant blog entries) revealed that occasionally, under certain conditions (air humidity in the 60% range and/or low room temperature below ~65F), the leading capstan would stop advancing the tape, with the unwanted consequence that the feed-in capstan would push the tape out into the space between the erase head and the feed-in pinch roller. Luckily, the auto-stop feature of the Beocord reacts fast enough to catch this happening before the tape gets damaged. One of these events is demonstrated at the beginning of the video below.
Experimentation revealed that pressing the leading pinch roller slightly towards its capstan with a finger solved the issue. Cleaning of the roller and capstan did not help much. And since the spring that controls the roller pressure looked pristine and its adjustment nut showed an intact B&O applied red paint spot, I came to the conclusion that most likely the rubber of the pinch roller had hardened, reducing the friction, causing occasional loss of transport. It is important to note here that the tape is transported forward by the friction between the roller and the tape, and not by friction between the capstan and the tape. The capstan only drives the roller via contact above and below the tape.
I searched a bit around on the web trying to find replacement pinch rollers for the Beocord, but to no avail. The issue is that the rollers have a fairly 'rare' diameter of 10.8 mm, which apparently was not used by any of the major tape mechanism manufacturers. It seems that most pinch rollers that were used back then were 1/2 inch. But surfing around on some 'tape heads' web sites and message boards soon yielded the name Terry Witt, who appears to be the only person on our planet who professionally rebuilds classic tape pinch rollers. I read some positive reviews about his work, and so I decided to get in touch. After a short email forth and back, I decided to extract the rollers of another Beocord that I had in my closet and sent them to him for rebuild. I was very pleased by the results! Here is a picture of the rebuilt rollers together with his business card:
The main challenge with the roller rebuild is to extract them from the Beocord's roller arms. Essentially, one needs to use a vise or press to push out the pins on which they run. Nothing for the faint of heart, but definitely doable. I made a YouTube video about the process:
I tested the deck by now for a few hours after inserting the rebuilt rollers, and everything seems to work great now. But I will only believe it after another couple weeks of testing...one realizes that mechanical issues are where the challenges lie with these old vintage units!
Tuesday, March 3, 2015
The last Beomaster 8000 PCB that needed its electrolytic capacitors replaced was the Filter and Tone control board that sits underneath the control panel of the unit. After unsoldering the signal strength meter leads, I removed the board from the control panel. Here are is a photo of the board in its original condition:
And after replacing the capacitors with new 105C types:
And a detail shot (the two AD13 ICs are the 64dB volume attenuators for the right and left channels):
Time to put the Beomaster back together and test the 3D printed control panel latch!