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Beogram 4002: Restoration of DC Motor Video Published - Check It Out!

By popular request (really, I got quite a few emails about this!...;-), I finally completed my Beogram DC motor restoration video! It demon...

Saturday, May 19, 2018

Beomaster 6000 (2702) restoration: final assembly and testing

After some delay caused by the need to recoat the key panel (see update here), it is now finally time to finish the assembly and start testing the Beomaster 6000 quad after this full restoration!

The display panel for the volume, tone and balance controls needs to be as close as possible to the red plexi panel for good readability. Therefore the frame on which the the display panel, motor controls, pulleys, clutches, tone amplifier PCB is mounted is adjustable. On each side on the frame there are 3 M3 bolts:  the middle one is to lock the adjustment and with the two other screws you can tilt and raise the frame.

Since you can not reach these bolts once the plexi panel is back in place, a different method is needed. I first attached the back black frame and the complete key panel to the main chassis. This was to have a reference point for adjusting.

I used a metal ruler and some pieces of wood (with the same thickness as the plexi panel) to make the adjustment.

An air gap of about 1mm is sufficient to leave enough room for the display bands to move freely and avoid rubbing.

Once this is done the keypanel temporary screws are removed and the plexi panel is put in place. The next step is to attach the wood plinth and the keypanel.

One last adjustment, before tightening the keypanel and the wood plinth, is the centering of the FM dial spindle/flywheel. This is needed because the keypanel had been removed for coating and glued back. There is always a bit of play. The spindle is rotating in two ball bearings. The top one is fixed in the square plastic holder just under the spindle. The square plate first need to be centered by loosening the 4 M3 nuts.

The second ball bearing is inside the shaft bushing at the bottom. This ball bearing is in a metal bushing that is adjustable with 3 bolts. If you loosen these 3 bolts the whole spindle can "wobble" a bit and allows to have the spindle surface flat and centered with the surrounding aluminium frame. This can only be done once the keypanel with the wood plinth is firmly fixed.

And finally the wire bracket is put in place.

Time for testing ! I attached 2 Beovox S45-2 as front speakers and 2 Beovox P45 as rear speakers. I also attached an Airplay device to play some music from my iPad.

And I had sound on all 4 speakers !!!!! 

A reflexion after this many, many hours of careful restoration of this iconic Beomaster 6000 quad: it's not a job for the faint of heart ! Was it a succes? Yes, definitely. Does it look and sound good? It sounds sweet to my ears. And it looks as good as one can imagine after some 40+ years of use. I've been at the Bang & Olufsen museum in Struer, Denmark, where there is (off course) one of these units on display (and fully operational). See picture below. And honestly, mine looks better ! 

I will now let it play for some days/weeks before I'll ship it to his new owner. 

Above picture is courtesy of the B&O Museum in Struer, Denmark.

Friday, May 18, 2018

Beogram 4004 (5526): Replacing the Light Bulb in the Sensor Arm with a LED Assembly

After replacing the transport lock bushings in the Beogram 4004 (5526) that is currently on my bench it was time to replace the light bulb in the sensor arm with a LED-based assembly. This shows the small bulb compartment pulled out of the sensor arm front:
The small flexPCB next to it is the LED circuit. Since modern high output LEDs have a much lower current draw than the original small light bulbs the LED circuit features a current bypass that adjusts the current to a level similar to the light bulb. This is important since there is a circuit on the main PCB that detects bulb malfunctions via current measurement, and the low current of LEDs would trigger this circuit, preventing the arm lowering mechanism from doing its job.

The flexPCB needs to be folded to fit into the bulb compartment. This shows the folded board next to the light bulb,
and installed in the compartment:
After replacing the compartment in the arm I tested the setup:
The B&O logo shows up with its usual red-orange glow. This is a result of using a warm white LED, which has enough red emission to properly illuminate the logo. The final step of any sensor arm light source replacement is measuring the sensor signal when the platter is spinning without a record on it. This shows the signal measured at the collector of TR3:
Each voltage drop corresponds to a black rib passing under the sensor. When everything is o.k. the drops should go close to 0V, while the amplitude should exceed 4V.  This Beogram 4004 passed the test with flying colors!

Monday, May 14, 2018

Beogram 4004 (5526): Installation of New Transport Lock Bushings

The Beogram 4004 (5526) that I am restoring right now had the orange type of transport lock bushings, which are prone to degradation. This was evident immediately after taking the Beogram out of the box, since there were telltale orange plastic fragments all over the place:
This shows the left transport lock without its bushing:

I removed the floating sub-chassis of the Beogram, which revealed the degraded remnants of all three transport lock bushings:
I vacuumed the enclosure, and then it was time to install the new 3D printed bushings:
Each bushing has two parts, one to be inserted from each side of the lock orifice. Like all parts featured on this blog they are available to other B&O enthusiasts. Order them directly via the Beolover Shapeways store. Six parts are needed for all three locks. This shows the lower part of the left lock:
And with the sub-chassis outfitted with a new bushing installed:
I also did this for the other two locks and then I replaced the top halves of the locks:
Now this Beogram can be shipped again without fear for damage due to loose transport locks.

Beogram 4002: Final Tasks, Adjustments & Playing Records

It is time to finish up this Beogram 4002 Type 5513 project. As a continuation of the corrosion damage repair I am replacing the 5-pin DIN phono plug.

Here is a nice reference diagram Beolover created a while back that shows the audio path from the MMC cartridge connector to the 5-pin DIN plug.

I like this diagram because when I am replacing the phono cable plug this shows the phono signals I check continuity on from the Beogram output board connector (P9) to the front of the plug.

Here is a picture of a continuity check for the phono right channel from the phono DIN plug to the output board P9 connector.

I installed a REAN 5-pin DIN replacement plug that has gold contact pins.

A note to other DIY folks that do this - Some of these Beogram phono cables have a cable diameter that makes installing the REAN rubber boot extremely difficult. The fit is really, really tight.

Another phono signal related change I made was to return to the output board and install a grounding switch between pins 5 and 6 of the P9 connector. That is signal ground and shield ground respectively. The Beogram 4002 units come with a separate grounding wire so owners can connect their Beogram chassis ground to an amplifier's chassis ground should there be hum in the signal path.
This grounding switch eliminates the need for that extra grounding wire as the switch can be flipped to short the two grounds together in the Beogram if needed. A nice option and the switch is easy to get to.

One last electrical task is to install the two RPM indicator light replacements (33 & 45 RPM lights). This upgrade of incandescent lamps to the Beolover LED replacement is not for cosmetic reasons. Beolover's ongoing testing of Beogram 4002/4004 DC platter motor stability has shown a positive measurable effect of the LED lamp assemblies over the incandescent lamps. So we recommend them on all of our Beogram 400x restorations.

One weak part of the Beogram 4002 design are the mounting clips for the RPM indicator panel into the control panel. The mounting clips are a hard plastic that often becomes brittle over time and cracks. This unit had a couple of hairline cracks so I applied some preventative patches.

I started the final reassembly of this Beogram unit which includes the service manual adjustments.

The first adjustment is for the Beogram platter height so that the distance from the top of the fixed arm (and tonearm) is 23mm from the surface of the platter. That adjustment is made using the large nut on the platter hub.

The tonearm lowering limit and pickup arm length adjustments are next.

That is followed by vertical and horizontal arm parallelism.

While the platter belt is still removed I adjusted the tangential arm sensor.

Now for the deck panels and the platter position adjustments.

Everything looks good. I performed the arm balancing adjustments earlier so the final adjustments are for the platter speed trim pots.

This Beogram is cleared for record play. I'll give it a listen as I document this blog post :-).

It looks like this Beogram is ready to go back home to Houston. Now where's my copy of "Houston El Mover"?

Sunday, May 13, 2018

Beogram 4004 (5526): Restoration of DC Platter Motor

After replacing the incandescent bulbs in the RPM trimmer panel with LEDs it was finally time to restore the DC motor that drives the platter of this Beogram 4004 (5526). This shows the motor extracted from the Beogram:
Restoration of these motors requires infusing the brass sleeve bearings with fresh oil under vacuum. this requires complete disassembly of the motor:
The Oilite brass bearings are the two small donuts on the black pad. I immersed them in motor oil and pulled a vacuum:
Immediately, air bubbles emerged from the bearings as the vacuum drew the air from the empty pores of the Oilite material. This enabled motor oil to penetrate the bearing material, refilling the empty pores. After about 48 hrs the bubbling stopped, indicating that the infusion process was complete. At that point I removed the bearings from the jar:
I reassembled the motor and put it back into the Beogram. Then I installed my BeoloverRPM device to do a 24 hrs RPM stability test:
The BeoloverRPM device is able to log the RPM of the Beogram for extended periods, which is a great way to detect and diagnose RPM stability issues. It is available to other B&O enthusiasts. Just send an email or use the contact form on the right if you are interested. This shows the RPM graph as measured after about 24 hrs:
This is as good as it gets for the Beogram 4004, and we can conclude that this deck is back on track to spin vinyls for another 30 years.