Beogram 8000: Installation of a Grounding Switch, Repair of a Broken Off PCB Post and, Finally!, Test Drive with Gabor Szabo!

I gave the Beogram 8000 that I am restoring right now a couple final touches:

1) As usual, I installed a switch that makes a connection between system and signal grounds. Such a connection usually extinguishes any hum that may arise from incompatible connections between turntable and amplifier. In my view there are no adverse effects resulting from connecting the two grounds, but the original B&O set-up is to keep them separately until they meet in the amplifier, so I put in a switch to make the connection easily reversible, if desired down the road.

This shows the installed switch on the output relay board:

2) I needed to reattach a broken off PCB mounting post. The post that holds the rubber bumper that presses the main PCB into its mounting brackets broke off when I removed the PCB...this old plastic can sometimes be a bit brittle. Luckily, there was enough 'meat' that allowed me to drill a small hole through the post and the underlying plastic with my Dremel tool. Then I bolted it down with a 2-56 screw and this worked very nicely:

All good now under the hood!

I closed it up and then performed a calibration of the tracking weight:

And then it was finally time for a test drive! I had just received a new vinyl from Sweden: Gabor Szabo's "Small World" from 1972. This is one of those he recorded in Sweden. I got the original Bellaphon release (Made in West Germany...;-)

What a great record (especially after ultrasonically cleaning it with my CleanerVinyl Pro..;-)! And his awesome 1970's purple outfit! Those were the days! The album contains another version of 'people', which is one of my favorite tunes ever. And Szabo brings it to life like no other. Too sad that his life was short and things did not end that well for him. Very unfortunate! I am very grateful, though, he left us a bunch of wonderful albums to enjoy! More achievement than most of us will ever be able to claim when we go meet our Maker for that final exit interview...;-)! This is Beolove!

Beogram 8000: Re-Attaching the Aluminum Panels

Time for getting pretty! The Beogram 8000 that I am restoring right now is now running nicely. But, like in most of these units, the aluminum panels are detached. Usually, it is no big deal to glue them back on. Here are a few impressions:

The panels were originally attached with some foam based double sided tape. The foam degrades and the panels come off. This is what one typically finds:

A gooey sticky soft mess! Very difficult to remove. I usually put ethanol drenched paper towel wads on there (make sure the veneer is not touched) and then wait for 30 mins:

After that the goo has softened up and can be scraped off with a plastic razor blade. Some residue remains, but this does not matter:

Then I usually glue 4-40 washers to the enclosure as spacers. I use quick setting epoxy:

Then I add some more epoxy on the top of the washers and place the aluminum panel:

Once it is in place, I secure it with carpenter's clamps and a weight for the top right corner, which is not accessible with clamps. This step is crucial, since one essentially only has one shot with epoxy. If you try this at home, make sure that the panel is really in the right spot. Applying the clamps often shifts the panel a bit, i.e. it needs to be kept aligned during the clamping process.

The next step was to put the lid back on. Unfortunately, someone already reattached it once with Gorilla glue and the panel came off again. The glue residue proved very well attached to the plastic hinge and I was not able to remove it.

since the glue residue was flat enough and its thickness similar to 4-40 washers, the situation could be rectified by adding a good amount of epoxy to the residue and more importantly to the regions that were uncoated in between, and placing the lid on top:

Again I secured it with clamps and used a pen to press the hinge upward above the power cord opening. This did the job!

Beogram 8000: Mechanical Adjustments, Carriage Belt and Spindle Lubrication

After restoring the brake circuit, the Beogram 8000 that I am restoring right now started to work again pretty well. But before a test drive I wanted to make the necessary mechanical adjustments, install a new carriage belt and clean the carriage slide mechanism.

Here are a few impressions of my progress:

The arms were quite out of whack. Both lateral,

and vertical parallelism were off considerably:

The lateral adjustment is easily done with a screw on the left side of the carriage assembly:

The vertical adjustment unfortunately requires that the carriage is take off the rails and turned around to get to the screw that is underneath:

This was the perfect moment to give the dirty spindle

a rejuvenating clean and lube:

I also cleaned the rods and put a bit of silicone grease on their surfaces. Then I put the carriage back on and checked the vertical parallelism:

Very nice! Add a new belt:

and the unit was close to be ready for a test drive. If there just weren't those (as usual) fallen off aluminum panels!

Beogram 8000: Repair of Platter Brake Circuit

After replacing the electrolytic capacitors of the Beogram 8000 that I am rebuilding right now and fixing the scraping subplatter issue the unit was again functional and ran smoothly at 33.33 RPM. However, I noticed that after pressing stop and the return of the arms to the home position the platter continued to spin for a long time until it finally came to a rest. The 8000 has a low friction bearing and there is no belt due to the linear platter drive. So there is very little friction overall once power is cut to the motor stator coils. That is why the designers of the Beogram gave it a motor brake that reverses the motor phases to essentially run it in the opposite direction for bringing it to a fast stop. That makes the humming noise when the platter comes to a fast stop.

This shows the relevant portion of the circuit diagram as shown in the Technical Product Information manual:

The motor stator coils are OL1. This are the two big coils that 'hug' the sub platter (which is the rotor of the motor). These coils are phase shifted by the motor cap 4C1. This is basically the same setup like in an AC motor 4002. The motor is driven by the Drive System, which is essentially a push-pull stage that follows the grid frequency taken from a dedicated transformer coil (4T1A) and which regulates the current through the stator coils that is produced by transformer winding 4T1B (the winding shown above the stator coils in the above schematic).
The brake circuit is is essentially formed by TR 31, TR32 and TR33. Once pin 37 goes low, TR31 is turned on (and the drive system turned off via TR27 and TR28). In the process TR32 turns on which then via D39 pulls down the base of TR33. TR33 turns on and the positive half wave of the 60Hz signal from the 4T1B winding is fed into the opposite end of the left coil of OL1 via D40. This reverses the motor phase relative to the normal signal.

The 'reverse drive' aspect of the brake system can be seen by a simple test: Connect the base of TR31 to ground with the unit in standby and the platter starts spinning backward!

It turned out that the brake malfunction in this unit was caused by a broken trace. The trace that connects the collector of TR31 to R110 was cut through, probably the consequence of a previous 'repair' attempt. This broke the chain of command between TR31 and TR32, so when the microcontoller said "brake!" TR32 did nothing, and TR33 remained off, which prevented the reverse phase signal to be applied to the stator coil. Since power to the coils was still cut via TR28, the platter simply spinned until mechanical friction finally stopped it...

Below is a photo of my fix: I soldered a small piece of 'magnet wire' between the relevant solder spots: Magnet wire is good for such tasks since it is coated with a special polyurethane coating (so one can wind a magnet without making short circuits between the windings) that burns off when touched with the soldering tip. Very convenient for making connections with short pieces of wire where it would be difficult to take the insulation of mechanically with a stripper tool.

After this repair the unit 'fired on all 8' again (ah the good old days when most real cars had a V8!)

On to mechanical adjustments and fixing the cosmetic issues of this unit!

Beogram 8000: Repair of a Scraping Sub-Platter with a 3D Printed Insert for the Main Bearing

The next item to look into with the Beogram 8000 that I am restoring right now was that the sub-platter scraped along on the chassis. This shows the interior of the 8000 with the sub platter still in place:

Somehow the platter was situated a few 1/10ths of a mm lower than usual, which made it touch the sub-chassis base plate in a few spots. This prevented the deck from maintaining a constant speed (it never showed 33.33 on the display, just 33, which is a signal that the RPM is off). Also it made an intolerable mechanical noise. Far from Beolovely! 

This seemed strange to me (there is no way to adjust platter height like one could in a Beogram 4002) and so I poked around a bit on the internet. I came across an uttering by one of the greats in this business, Dillen of Beoworld: "Typical symptom of a broken main bearing nylon insert. It happens often if the Beogram was transported with the heavy platter mounted or just put down too hard." (my customer confirmed that the ebay seller did not take out the main platter when he/she shipped it to him...).

He went on to say "The whole weight of the platter, hub and sub-platter rests on the very sharp pointy tip of the hub spindle. Only fix is to replace the nylon insert."

This shows the spindle after lifting out the sub-platter:

In the pic the tacho sensor is already out of the way (it swings away by moving the brass lever clockwise). In that position one can pull out the spindle:

The picture shows the pointy end of the spindle that rests on the plastic disc that Dillen mentions in his post.

The plastic disc can be pushed up using a small hex wrench or similar (there is a small hole on the bottom of the bearing that can be accessed from underneath the enclosure. This shows the white plastic (probably nylon) insert in the main bearing:

And after pushing it up:

First I tried to simply flipping it around, but there is no indentation on the back of the plastic part for holding the spindle in the center of the bearing. So my idea was to simply shimming the insert up a bit to lift the platter back to its normal height. The insert still seemed in decent condition, only the indentation was a tad too deep after the incident, causing the platter to be too low. 

I designed a small disk that I printed with my 3D printer:

After a few tryouts with different thicknesses it turned out that 0.7 mm was a perfect thickness to raise the platter just enough to not scrape anymore (test with the main platter and a record on top if you do that at home...).

The disc is easy to insert when the insert is up sideways:

Once the printed disc was next to the insert, it is straight forward to push the parts back to horizontal and down into the bearing.

Once I installed the spindle and the platter again, everything was fine. No more scraping, and the platter turned freely.

Beogram 8000: A New Arrival and Restoration of the Control System

A Beogram 8000 in need of some TLC recently arrived. It had been purchased on ebay with two MMC20 CL cartridges...very nice!. Unfortunately, it did not work anymore upon arrival at its new owners location. So it traveled on to my place and here we are:

The unit has the usual fallen off aluminum panels. Luckily someone catched them before they hit the floor and they are unscathed. Overall this unit is in pretty good condition and all seems original (if there just weren't the tough layer of Gorilla glue on the hinge of the smaller aluminum panel):

I opened it up and found a slightly dusty interior, but nothing otherwise unusual:

Then I had a look under the sub-platter where I found a metal tacho disk:

This is great news since the original plastic disks tend to delaminate, which causes severe RPM instability.

So far so good. When I tried to run it the platter would not spin, and the carriage showed some reluctance to move. Nothing unusual at this point in time for a Beogram 8000 in original condition. When the platter has trouble moving, it usually has to do with bad power block connections or a dead motor phase capacitor.

I decided to go ahead and rebuild the electronics. This involves replacing all electrolytic capacitors with modern Japanese major brand 105C types and reflow all the board to wire headers solder points. They are often cracked and this causes intermittent operation of the deck. Here are a few impressions. This shows the main boards taken out:

Most of the capacitors are straight forward to replace. The one that is usually a bit of a pain is the processor power supply decoupling capacitor in the EMI can. I took the can off the board and opened it up:

The processor was stuck to the can lid and popped out of its socket...In those days these chips were quite expensive, and so they used sockets instead of soldering them in directly. For exchanging the capacitor a removed processor is perfect. So I left it stuck to the lid for now. The picture below shows the original 47uF capacitor in question. It makes the GND connection (left) on top and not on the bottom solder point, which are not connected by a through plated via like one would expect on modern boards. This can be confusing since failure to solder it to the top contact pad will cause erratic processor behavior. I once spent an entertaining evening with an 'exploration' of this issue...see here for a description of that Beolover adventure...;-).

Anyway, I exchanged it:

and then I removed the processor from the can lid and inserted it back into the socket and replaced the lid and mounted the can back to the board. This shows the recapped board with the removed original components placed next to it:

After that I reflowed the solder points of the headers. This is best done by adding a bit of solder to each point. The boards were soldered with relatively sparse solder application, which may be one of the reasons that so many Beogram 8000s have bad joints. Indeed, I found several cracked points, mostly on the main power block header. This shows the pins where the motor phase capacitor is connected:

Both have a telltale ring around the soldered pin. This probably explains why the platter behaved erratically. I resoldered everything and then it was time to put the board back in. The next step was the replacement of the motor phase capacitor that is located in the power block:

I usually replace this big can with two modern 47uF bipolar units back to back. This turns them into a single 23.5uF unipolar capacitor, which works perfectly. Since modern capacitors are much smaller I recently designed a 3D printed insert that holds the two caps neatly in place:

After reinstalling the power block I rebuilt the power supply board that is next to the sub-platter:

It has only two reservoir capacitors that need exchanging:

This concluded the restoration of the PCBs, and it was time to do the carriage servo control voltages adjustment to the prescribed 620mV (err on the smaller side if you must, this adjustment can be a bit sensitive):

And then it was time for a test! And as expected the Beogram fired up normally with the platter moving smoothly and the carriage looking for a record. All good in control system land! On to the mechanical parts of this lovely deck!