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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...

Monday, September 18, 2017

Beogram 8000: Testing The Restored Components

All of the key Beogram 8000 components have been examined and restoration work was performed where necessary. Now it is time to connect them up and see where things stand functionally. This is the most exciting time of the restoration (other than the first play of a record).

I plugged the Beogram into the AC power socket and started checking the main voltages. All were present and accounted for.

The red standby dot was lit on the display so I pressed Play and observed the Beogram come to life and search for a record to play.

The tangential arm assembly moves across the platter looking for a record. The lamp and sensor in the fixed arm send back a triangular signal when no record is on the platter.

Here is the detector arm circuit and measurement with my oscilloscope.

The signal looks just as expected and the Beogram correctly determined there was no record at both the 12 inch record and 7 inch record locations.

Another sensor voltage I check is really two signals that come from the tangential arm drive system. Two pulse signals from sensors reading the rotating arm drive screw, feed the Beogram sensor counter.

Here is that circuit and the measurements.

Both signals are working well. 

The next sensor to check is platter speed.  This is the sensor that reads the metal tach disk. The pulses feed the Beogram microcomputer where the speed is automatically adjusted to either 33 1/3 or 45 RPM.

Here is the circuit and measurements for both platter speeds.

As a reference I put the channel 2 scope probe on the microcomputer PCB 5 VDC power.  Everything looks great with the speed sensors. The Beogram immediately changes speeds and locks in to which ever speed is selected.

I can also report that the tangential arm assembly is moving easily and is very stable with the repaired arm drive bearing installed.

There is one more set of sensors I will measure and adjust tomorrow. Those are the two LDR sensors for forward and reverse scanning. I want to install my usual test connector for those so I can re-check those sensor voltages after these components are installed back in the Beogram cabinet.

Saturday, September 16, 2017

Beogram 8000: Fabricating a Fix for the Tangential Arm Drive Problem

Since I have the two broken pieces of the tangential drive bearing for the Beogram 8000 I thought of a way I could fabricate a repair. Any attempt to glue the tiny broken tab back onto the bearing by itself would be pointless. There isn't enough surface to attach it so that it wouldn't just break off again.

I re-installed the rear rail, drive screw, bearing and bracket to check what the clearances are around the bearing. There is plenty of room to add some reinforcement to the broken side of the bearing in the fix attempt.

What I needed was something I could epoxy all the way around the broken side of the bearing. My solution for that was to find a flat nylon washer to fit the job. After some experimenting I found that a #10 (SAE) size washer would be a good candidate. 

To glue the nylon washer to the broken side of the bearing I needed a clamp. It turns out that an M5 - 0.8 screw, washer and nut work perfectly as both a clamping mechanism and a secure mount for the bearing. The tangential drive screw is also an M5 - 0.8 threaded part.

I glued the washer onto the bearing first and let it begin to set up.

The broken sliver of plastic that was the bearing tab snugly snaps into the space between the washer and bearing. All I needed to do was add some epoxy there and everything will bond up nicely.

I let that dry for a couple of hours then removed the repaired bearing from the makeshift clamp. A test fit shows promise that this solution will work.

Tomorrow I will re-assembly the various Beogram components and see how close I am in having this turntable back in operating condition.

The best solution for this problem will still be to create a 3D replacement part. I was lucky in this case to have the broken tab piece to fully build the bearing part back up. Had that tab piece been unavailable (as is the case with some of my other spare Beogram 8000 units), I would have probably tried to build and wall there with some epoxy. Fortunately I didn't have to deal with that scenario.

Beogram 8000: A Tangential Arm Drive Problem

In cleaning and lubricating the Beogram mechanics one of the first things I wanted to check on is the small plastic bearing that travels the tangential arm drive screw to move the tangential arm assembly across a record and back to the rest position.

I wasn't too surprised when I discovered the bearing had a broken tab on the side that pushes the arm assembly back to stop. That seems to be a pretty common state in these Beogram 8000 units I am seeing.

In the last Beogram 8000 project I ran into this exact same issue where the round, plastic arm drive bearing (I called it a bushing in that post) had a broken tab where the mounting bracket attaches. I was able to re-attach the bracket and the Beogram was able to function. After returning the turntable to its owner the Beogram had problems with its arm lowering. I had the Beogram shipped back to me to discover that problem was due to a piece of FOD interfering with the arm lowering mechanism. That FOD piece was the broken tab off the plastic drive bearing!

I immediately looked at the arm lowering mechanism of this new Beogram 8000 turntable and sure enough, there was the broken plastic piece sitting in the compartment where the arm lowering mechanism is. This is indeed the same problem as the last Beogram 8000. Now that is a surprise.

Here is a closer look at the broken arm bearing pieces.

As I said earlier, this appears to be a common issue with these older Beogram 8000 turntables. Extra force must be being exerted on that part of the bearing when the tangential arm assembly is moving. Perhaps it starts failing as the Beogram electronics begin to fail and the arm drive system malfunctions.

Also as I mentioned, the Beogram can still function with the broken drive bearing tab. However, the drive shaft will likely make a noticeably louder sound when traveling the direction that is pushing on the broken tab. The real solution is to replace the bearing with a fully intact one. I do have some spare Beogram 8000 units but all of them except one also had arm bearings with same broken tab. I used that intact bearing on the previous Beogram 8000 project.

Now I will have to look for a new solution.

I might be able to fabricate something I can epoxy on the side of the bearing with the broken tab but a better solution would be to come up with a 3D printed replacement part.

I am going to start looking at these arm drive bearings on all of my Beogram 8002 turntables to see if any of them have this problem.

Beogram 8000: Finishing the Capacitor Replacement

To finish up the main PCB after the capacitor replacement I swapped out the two bad board connectors - P5 and P6. In addition I re-flowed the solder joints on all of the board connectors.

The next capacitor update was on the platter drive capacitor 4-C1 that is located in the Beogram transformer case. Because the new replacement is much smaller Beolover made a nice capacitor mount using a 3D printer.

The final two capacitors to replace are the chassis mounted 0-C1 and 0-C2 capacitors (1uF and 47uF respectively).

That completes the bulk of the electrical restoration. There may some additional electrical component restoration depending on if any of the Beogram sensors or lamps have failed. 

I am anxious to try out the recapped circuitry so the next task on my to-do list is to clean and lubricate the tangential arm assembly. 

Friday, September 15, 2017

Beogram 8000: Replacing Capacitors On The Main Boards

Restoration work on this latest Beogram 8000 project begins with the main boards. I will replace all of the electrolytic capacitors with new, high quality, Japanese 105°C capacitors. Most of the time I use Nichicon, Panasonic or Elna capacitors. Where possible though I use WIMA polyester capacitors where capacitance values are 4.7uF or less.

Here is the main board with the microcomputer board and two small B&O mod boards attached.

The most time consuming PCB work is on the microcomputer PCB. There is only one electrolytic capacitor on that board but it is in a difficult place. Here is the microcomputer PCB opened up.

The 47uF (C28) capacitor has its positive lead soldered on the trace side of the board while the negative lead solder point is on the component side of the board. This capacitor is for the +5 V power supply to the integrated circuits on this PCB.

 I usually replace the microcomputer IC socket while I have that board open. The original socket is not as rugged as the modern socket I replace it with so it is a good upgrade.

Here is the microcomputer board with its new C28 capacitor and microcomputer socket.

NOTE: Because the microcomputer IC had to be handled I made sure to wear an anti-static (ESD) wrist band.

Now it is on to the main board. I start with the three largest capacitors - C27, C24 and C29.

Old audio components usually begin to fail due to one or more key electrolytic capacitors failing. I find that most of the capacitors are still within their tolerances but there are always some on the edge of their limit or failed. That is the reason we go ahead and change them all out during these restorations.

On this Beogram the C24 2200uF capacitor had failed where it is way out of tolerance. It should have measured over 2000uF instead of just 475uF.

Quite a few others were also out of tolerance or on the edge of their limit.

The original C27 capacitor came with a three prong base to secure it to the PCB. This base is not found in modern replacement capacitors so I snap the original base off and re-use it with the new C27 capacitor. This makes for a good fit and I put a bead of hot glue around the base to secure the capacitor more than just the soldered on negative lead.

When I removed the original electrolytic capacitors and started to replace them I noticed that three of the black press-to-fit board connectors had deteriorated and were damaged (shown outlined in the next photo).

I always re-flow the solder on the board connectors anyway so after I finish recapping the board I will replace those damage connectors with some I have from a spare Beogram 8000 main board.

Here are the main board, microcomputer board and mod boards after recapping.

I will reflow the connector solder joints next and replace the damaged connectors. After that I will recap the motor capacitor in the transformer housing and the two capacitors that are mounted on the Beogram floating chassis. Once all of that is completed I will be able to test the Beogram electronic operation.

Sunday, September 10, 2017

Beogram 4004 Type 5526: Cleaning and Polishing the Dust Cover

The Beogram 4004 turntable has been test playing in my office listening room for a couple of weeks now. All that is remaining on this project are a couple of cosmetic issues. One is polishing out some minor scratches on the dust cover.

The procedure for this is time consuming because it takes a number of wet sanding steps using finer grit sanding material on each step. After each sanding step I rinse off the excess sanding residue and dry off the dust cover for inspection. Then I rotate the dust cover ninety degrees for the next step so each step is perpendicular to the previous step.

Here is a picture of the Beogram 4004 dust cover prior to beginning the work. It is hard to capture the true severity of the scratches in a photo but you can see there are scratches on the dust cover. I have seen much worse but these are still worth polishing out.

Here is the dust cover and all of the polishing tools laid out on my fabrication table.

This picture shows what to expect after the first wet sanding step. In this case I started out with 600 grit wet sandpaper because there are not any real deep scratches on the dust cover.

After going through 600 grit to 2500 grit sanding steps I reached the 3000 grit sanding step. That is the halfway point in my progression.

Here is the dust cover after the final sanding step of a 12000 grit Micro-Mesh pad.

It is starting to look good again but you can see it is a little hazy by looking at the sanding tool packaging text under the dust cover.

After a buffing polishing step using an eccentric orbiting pad on my power drill the dust cover clarity really comes back.

Here are two pictures of the polished dust cover similar to the two I posted of the dust cover before starting the work. The scratches seen earlier are gone.

This dust cover looks like it is ready to be re-installed on the Beogram.

Saturday, September 2, 2017

Beogram 8000: New Arrival From The Motor City

A new Beogram 8000 project arrived yesterday. It is a restoration project and sounds like it has the typical problems this type of Beogram usually develops after almost forty years.

The turntable doesn't function correctly, the aluminum deck trim and tonearm compartment lids all have deteriorated attachment material (double-sided tape).  These are all things that can be remedied with new capacitors, solder re-flow, cleaning, lubricating and new mounting tape.

Here are pictures of the turntable before I start the work.

The first thing was quite a surprise. This Beogram arrived packed pretty well...styro-foam all around and tightly bubble-wrapped. However, it was not double-boxed and most importantly, the floating suspension was not locked down. The MMC-20CL cartridge was left mounted on the tonearm and the stylus guard was not attached. Very, very fortunately nothing appears to be damaged from the trip. A congratulations and thanks can go out to the delivery guys for their handling on this one.

The aluminum deck panel is loose like almost every Beogram 8000 still in their original state. The mounting tape is all deteriorated now. That old tape residue will be cleaned off and new 3M automotive double-sided tape will replace it.

The same problem exists with the bottom deck panel in the tonearm compartment.

Under the sub-platter I discovered the mount for the tachometer sensor guard had come loose. The locking washer/clip was loose inside the Beogram case.

Here is the Beogram case with the turntable floating chassis removed. On these restorations I prefer to remove everything to work on the individual assemblies separately rather than work on everything together and still attached. I believe there is less risk of accidentally damaging other components that might get in the way.

Here are the electronic components after they have been removed. The boards will get new electrolytic capacitors and all key solder joints will be re-flowed. I will also change out the IC socket for the processor with a new and better one.

One component I always want to protect is the dust cover assembly. By removing it I get it out of the way and makes it way easier to work on the tangential arm transport.

A word of warning - The Beogram 8000 and 8002 dust covers are a little tricky to remove. I use plastic pry tools like you find for working on cell phones.

The back of the Beogram dust cover attaches by a long plastic lip and a few plastic tabs. Many times there are broken and missing tabs because someone has yanked the cover off instead of carefully maneuvering the back of the cover to clear the tabs and lip.

The picture above and the next picture show the metal tab with the two hooks that mount the dust cover lid to the main Beogram cabinet. This must be the first thing detached when removing the dust cover assembly.

This last picture shows the tonearm compartment lid and deteriorated mounting tape. It will also be cleaned and new 3M automotive tape applied.

Now that the Beogram has been disassembled for restoration the real work can begin. I didn't find anything in the disassembly that is unexpected for this type of turntable. All of the original parts are there and intact so I am anticipating a straight forward restoration project without any weird surprises ( but then I almost always say that).