Beogram 4002 (5513): A New Arrival from Colorado - First Assessment

A while ago I received a Beogram 4002 (Type 5513, with DC platter motor) for restoration from a customer in Colorado. Today was the moment to put it on the bench. The unit came safely packaged in a Beolover box and so all went well. I extracted the unit from the box:

The hood is pretty scratched, but could be polished on the outside:

Its hinges do not seem cracked, but there are a few marks on the inside of the hood. So even after polishing it will be a bit of a 'place holder' until new reproduction hoods may become available again at the dksoundparts store.

When I opened the hood, I found a liberated solenoid plunger:

This is how the aluminum surfaces look like:

Pretty good, but the keypad has the usual smudges and the coating is work through in some spots:

Luckily this can be fixed with one of Beomazed's reproduction keypad plates.

The plinth wood frame is in decent condition. It has a few dings but the front corners still look pretty sharp:

It needs to be re-glued, however:

The brushed aluminum surfaces are pretty good, albeit the platter has a bit of minor scratching:

I removed the platter and the aluminum panels and had a look below deck:

The unit seems to be in a fairly original condition, but there are signs of 'human creativity'. The carriage pulley, which is notorious for cracking at the set screw, was fixed in a unique way:

I also found a non-standard retaining 'washer' trying to hold the solenoid lever down on its pivot point:

The original washer probably got lost during a repair.

After this visual inspection I plugged the unit in and pressed START. The carriage started sluggishly towards the LP setdown point and found it. As expected, no solenoid action was discernible due to the absent plunger. The platter motor had also come to life and it rattled noisily due to dried out motor bearings.

In summary, all encouraging life signs! This unit is a decent starting point for a restoration.

Stay tuned for my followup post discussing the work done to bring it back to a like-new performance and look!

Beogram 4004 DC Platter Motor Restoration Using Dksoundparts Bearings

I recently received the DC platter motor of a Beogram 4004 from a customer in the Netherlands. This customer wanted me to install new reproduction bearings he had purchased at the dksoundparts store.

Normally, I re-infuse the original bearings with oil under vacuum. So it was an interesting experiment for me to see if there is a difference in outcome. 

This shows the motor as received:

I took it apart as usual:

The original bearings are on the black pad up front.

The new dksoundparts bearings came in a small metal can:

I took them out of the can. They are oily since they were also infused with oil under vacuum:

This shows them installed in the top and bottom parts of the enclosure:

If you try this at home, make sure the larger bearing goes into the top part and the smaller into the bottom.

After closing the motor up it was time for a 24 hrs RPM stability test with the BeoloverRPM device:

In its 'slow' mode the BeoloverRPM sends an RPM measurement every 10 sec to a computer serial port.

This is the curve I measured after about 24 hrs:

This curve looks a bit 'wilder' than the curves that I get for most of my restorations using the original bearings (see for example this restoration project for a comparison). This does not really come as a surprise to me since over time I came to realize that it is important to re-install the original bearings in the same orientation as they were installed originally. This significantly shortens the time it takes to break in the bearing. It seems the bearing surface gets polished around the main contact area defined by the pull of the platter belt, which over time lessens the amount of RPM fluctuations. 

When installing new bearings there is no already polished area, so they always need to get broken in. I expect this motor will probably clam down after playing it for a few hundred hours. I suspect that new Beograms back in the 1970s had this issue, too, but no one noticed it since these variations are well below the threshold humans can detect.

I thought it would be interesting also measuring wow and flutter (short term RPM variations introduced (mainly) by the feedback loop that keeps the RPM constant in DC motor Beograms).

This can be done in 'fast' mode with the BeoloverRPM.

This is the curve I measured during about 60 platter rotations:

In fast mode the BeoloverRPM logs a RPM measurement every time a platter rib passes under the sensor. In other words one gets 24 measurements per rotation. The above graph looks 'complicated' since the actual RPM variation measurement is superimposed by a measurement artifact caused by minute variations in spacing between the platter ribs around the platter. Since the time between ribs passing is measured and then converted into an RPM value, changes in the spacing results in proportional changes of the calculated RPM. This causes the observed zig-zag pattern (the 'platter pattern'), which is added to the actual RPM variation. The true RPM variation in turn corresponds to the slower wave pattern that is superimposed onto the platter pattern. An evaluation of the graph seen here suggests an RPM variation of maybe 0.2%. 

When using the original bearings I usually get something around 0.1%, i.e. a slightly better performance. This probably also has to do with the rougher surface inside the new bearing that challenges the feedback loop a bit more causing more variation.

It would be very interesting to measure this motor again in a couple years after this Beogram played a few hundred records. I would expect to see a better performance.

After this experience, I think one can say that it may be better to use the original bearings if possible. But the new bearings available at the dksoundparts store are a viable alternative if a vacuum setup is not at hand. It would be interesting to know how the results with new bearings compare statistically, i.e. after doing a larger number of motors with them. What I know from my restorations with re-infused original bearings is that in a small number of cases (<5%) the restoration results can be less than satisfactory.

In general, this discussion is pretty academic since even 0.2% variations are much smaller than the 0.7% threshold where humans begin noticing pitch variations.

In summary it can be concluded that this motor is ready for duty again! Time to send it back to the Netherlands!

 

Beogram 8002 Hood Replacement

 The Beolover recently received a Beogram 8002 from a customer in California. As part of the restoration, the customer elected to have the hood replaced with a new one. Luckily, these hoods are now available from the Beoparts store.

The main issue with the reproduction hoods is that you don't get the original trim strip that has the model designation. Beoparts does offer a replacement trim, but it's not an exact match for the original (the original varied over time also, some are brown, some are black), so the best solution is to try to preserve the original.

This is the condition of the original hood, it shows the typical wear and tear:

A lot of that damage could be avoided in the future by using softer cleaning solutions such as a damp microfiber cloth. Windex and paper towels are abrasive to plexiglass.

Believe it or not, the photo below depicts the first step in the process I use to extract the original trim. It took several attempts to get this process perfected, I wouldn't recommend it unless you have spare hoods!

The reason for cutting the hood like this is that it's too difficult to work with the large hood and its structural rigidity causes more stress on the trim piece. When cut down to this size, the hood is more flexible and can flex away from the trim, without bending the trim. I apply heat for an extended period of time to loosen the glue and I am then able to pull them apart:

The back side has a layer of glue which must be removed, the X-acto #17 is perfect for this:

Back is pristine, ready to be glued down to the new hood:

The front looks great, has a minor scratch:

I then use masking tape and paper to protect the surfaces while spraying high bonding strength adhesive on the back side of the trim and top of the new hood:

Here's a peek at the final product, which the Beolover will be completing very soon:

Beogram 4002 (5513): A New Arrival from California - A First Assessment

I recently received a Beogram 4002 (Type 5513, with DC platter motor) for evaluation. My customer wanted to know whether the unit could be brought up to a functional state on a budget, or whether he should sell it to the Beolover instead.

This shows the unit as extracted from the packaging:

It has pretty decent aluminum surfaces. The hood has the usual scratching but no obvious cracking around the hinges, so could be potentially polished and returned to a decent state. The wood plinth probably should be replaced with a new CNC machined frame if a pristine look is desired. The left corner could be re-glued

but the right corner is chafed at the bottom:

The keypad has the usual use traces:

This could be fixed with a new reproduction keypad plate.

I removed the hood

and the aluminum plates and platter:

Below deck this unit seems largely original. A visual inspection revealed missing hood bolt springs:

Also the transport lock bushings are degraded as usual as is evident from the many orange plastic fragments found throughout the enclosure:

Likewise the plastic plinth guidance washers are gone:

Another plastic part failed, too: The carriage position sensor housing has lost one of its legs. It is still hanging on due to it being also glued down with double sided tape:

This should probably be addressed by installing a Beolover Carriage Position PCB for Beogram 4002 and 4004. This recently made available board represents a modern redesign of the carriage position detection circuit using a monolithic IR photo-interrupter whose signal is cleaned up and shaped by an opamp in combination with a Schmitt trigger. This alleviates the sometimes tricky implementation/adjustment of new sensors and/or LEDs on the original board.

Then it was time to plug this unit in and press start for the first time. I could not help noticing the mouse bites on the power cable:

It always amazes me that rodents would prefer nibbling on plastic insulation instead of venturing out and finding a nut or something else that is nutritious and tasty! They must have a different worldview!...;-).

I pressed START and the carriage started sluggishly moving towards the LP setdown point, which was found and the solenoid engaged. All good signs. After disassembling, cleaning and re-lubricating the carriage mechanisms should work o.k. again.

The platter motor ran pretty noisily, also nothing out of the ordinary. These motors usually need a restoration before a reliably constant RPM can be achieved again.

In summary, I would think this unit could be a decent candidate for a full restoration resulting in a like-new Beogram fit for reliable day-to-day operation.

Beogram 4002 (5503): Intermittent Tracking, Installation of New Carriage Motor and Restored Keypad and Update to Latest Beolover State-of-the-Art

I recently received a Beogram 4002 (5503) that I had restored in early 2020. After running for a while it came back in August 2023 with a fried H-Bridge. The H-Bridge is responsible for driving the DC carriage motor. It allows reversing the current direction even if there is only a single positive voltage rail in the system. It does that with transistors that act as switches to reverse the polarity on the motor leads. These transistors need to be able handling the motor current. If everything goes well, the current capacity of the transistors is safely above the current drawn by the motor in all operational situations.

Electric motors draw more current when they run under load since they run slower at the same applied voltage. The slower RPM causes the motor back-EMF (the self-induced voltage in the motor, which is opposed to the driving voltage) to be lower, so more of the applied voltage arrives at the motor coils, which in turn increases the current in the motor windings. This is a great feature of electrical motors since it means maximum torque at zero RPM, great for burning some rubber at a green light to impress ICE vehicle drivers (whose torque-to-RPM ratio is reverse: Minimum torque when the car is at rest and maximum torque when it is at speed...;-).

But this also means that if a mechanical system that is driven by an electrical motor develops more friction over time due to hardened lubricants or dry motor bearings, the motor will draw more current than when the system was new.

I finally came to realize over the years that this may be the root cause for H-bridge failures in Beogram 400x. The H-bridge transistors are able to handle currents of 1 Amp max. And when everything is according to spec fast forward or reverse typically draws about 0.1-0.2 Amps. 5x is a decent safety margin. But when there is additional friction, the current can get dangerously close to 1 Amp or even exceed it. This is evident from the often found blackened PCB surfaces under failed H-bridge transistors.

The main reasons for this issue are the carriage motor itself and hardened lubricants in the carriage translation mechanism. The latter can easily be addressed by cleaning and re-lubricating, but in the case of the motor replacement is necessary. In difference to the later DC platter motors, these motors cannot be rebuilt easily. This was the reason I designed a replacement motor that draws less current than the original motors at a similar torque. Due to its modern design it also creates less vibrations and noise compared to the original motors. This post describes an evaluation of my design.

So I am not really surprised anymore that this Beogram came back again with carriage drive issues considering the earlier H-bridge issues. This time it sometimes stopped tracking. An indication that the carriage motor developed even more friction in its bearings since the last visit. 

Therefore, the first step was to replace the carriage motor with the new Beolover Carriage Motor for Beogram 4000, 4002, and 4004:

This shows the original motor in place:

I extracted it and opened the enclosure up:

Then I installed a new Beolover motor:

It is a bit shorter, which permits feeding the leads through the hole in the enclosure bottom for convenient routing. This shows the motor in place:

After the motor I also replaced the H-bridge power transistors, which were potentially compromised due to the too high current draw of the carriage motor. This shows the H-bridge as I left it in 2020:

I removed the four transistors:

1TR25 definitely got a bit hot as suggested by the browned PCB surface under it. This transistor participates in driving the carriage left towards the home position. This is probably the most stressed one since every time the carriage returns home it goes full speed for maybe 20 sec giving this transistor some time to heat up.

I installed a new set of transistors and then it was time to update the RPM panel backlight LEDs. I had replaced the bulbs in 2020, but back then I still used homemade boards featuring red/green LEDs tuned to yield an incandescent sheen. This shows the bulb covers of the RPM panel:

I removed the covers, which revealed the LED boards I had installed:

I removed these PCBs. This shows the old design together with my current solution:

The new boards solder directly to the solder points of the original light bulbs. They essentially act as an extension of the circuit board. This shows them installed:

They give the RPM adjustment scales a nice incandescent-like backlight:

My customer also wanted me to update the main capacitor setup and the wasteful linear regulator based 22.8V power supply. This shows my work of 2020, when I still used big radially leaded capacitor cans similar to the original setup:

I removed this setup and installed a Beolover Efficient 22.8V Power Supply and Main Capacitors for Beogram 4002 (Types 550x) board:

This board solders directly to the existing leads that previously connected to the big capacitors. The board also replaces 0TR1 (to the right of the platter motor in the picture) that regulates the 22.8V rail in the original setup. My board uses a modern buck converter to create the system voltage from the rectified DC coming from the transformer, which is much less wasteful and results in a cooler running and less energy using Beogram.

Looking at my notes from 2020, I saw that I did not de-magnetize the solenoid plungers yet as a standard restoration item. These plungers often get magnetized to various degrees, which can result in sluggish arm lifting. During auto-return at the end of a record this can cause the tip to drag over the platter for some distance before it finally lifts up when the spring overcomes the magnetic attraction. For demagnetizing the plunger the solenoid has to be extracted and then the plunger unscrewed from the angled bolt that connects the solenoid lever. This shows the solenoid in place:

Indeed the extracted plunger was magnetic. I usually test this with a ferrous set screw. If the plunger attracts the screw it needs demagnetizing:

After using my tape head demagnetizer on it a bit the screw was not attracted to the plunger anymore, 

so I put everything back together.

I also found that the sensor arm LED replacement was still one of my early versions based on a home etched flex PCB that I folded into the small bulb compartment:

This shows the extracted old part in comparison with my current approach, based on a small PCB and a 3D printed alignment aid:

I installed the Beolover Sensor Arm LED Light Source (for Beogram 4002, 4004 and 4000):

This shows it in action. It uses a warm white LED that has enough red photons for lighting up the B&O logo in a realistic warm red:

Next came the replacement of my original early design transport lock bushings. The one on the left in the picture below shows my original design, which has a much wider wall thickness. Over time I came to realize that it makes the adjustment of the sub-chassis much easier if there is a bit more room around the lock bolts. So I re-designed the bushings with thinner walls (shown on the right): 

An added nice benefit of these new bushings is that the sub-chassis can move much more before it hits the lock bolts. This gives gives it a much more supple feel when the platter is touched and just freely swings. This shows one of the bushings installed:

Their two halves are simply pushed in from the top and bottom, which makes installation very easy. This shows the liberated chassis during the installation of the bushings:

The final update was to replace the smudged keypad with a new Beolover replacement. This shows the original keypad:

Most of the 4002 and 4004 keypads develop such use traces over time. First it starts with such 'smudges', basically polished areas caused by friction with the fingers when operating the Beogram. As time goes on the coating wears fully through. Luckily co-Beolover Beomazed recently succeeded after a long time of trial and error with reproducing the keypad plates. His plates are completely new and carry a modern resilient coating that promises to last for a while. This shows the restored keypad:

Absolutely stunning. They really look like the original pads! Read here how he does it!

If you are interested in getting your keypad restored, please visit here.

I installed the renewed pad in the Beogram. This is how this beauty looks now!:

And then it was finally time to enjoy this fully Beolover state-of-the-art restored Beogram with one of my favorite records by Chico Hamilton: "chic, chic, chico", which he recorded in 1965 on Impulse! I have the stereo version AS-82. He looks really chic on this one!...;-). A stunning record that has just the right amount of 'avant-garde edginess' as one would expect from an Impulse! record! A great match for this beautiful Beogram 4002!:

I will now play a few more records on this deck and then it will be time to send it back to its owner in California!