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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...

Wednesday, November 23, 2016

Beogram 8002: Replacing the Motor Phase Capacitor

Today I finished up the recap of the Beogram 8002 that I am restoring right now. The motor phase capacitor is hidden away in the transformer block:
This large can is a unipolar 27uF capacitor. It can be replaced with two modern back to back 47uF bipolar caps. I designed a 3D printed fixture to hold them neatly in place:
This assembly is available to other enthusiasts. Just send me a message via the contact form to the right.
After this was settled I went on to replace the two remaining power supply capacitors that are directly soldered to the small PCB that uses the enclosure as heat sink:
I soldered two new capacitors in
and that concludes the electrolytic capacitor renewal of this Beogram 8002.



Sunday, November 20, 2016

Beomaster 8000: Input Selector Trouble - Tuner Audio Mixed with Phono or TP1 Inputs

*************************Achtung: There is a follow up to this post. **********************

Oh well...I ran the Beomaster 8000 that I finished up recently for some time in my Beosystem 8000 setup and all was well, but then it developed a strange issue: When switching from FM tuner to Phono the phono signal was audible, but the tuner signal was still there in full strength. So instead of switching from one input source to another the Beomaster decided to mix them together instead! So back to the bench it went!

After I opened it up I discovered that I could provoke the issue by wiggling P82 on the uprocessor board. P82 transmits the microcontroller's wishes to the input switches on the preamp board. So this made immediately sense: The FM input did not get turned off when opening up the Tape 1 or Phono inputs due to an intermittent connection (the audio input switches on the preamp board are basically gates that open and close depending on high/low control signals from the processor).

First I thought it was a plug issue, and I cleaned the contacts a second time and bent the header bins a bit to give everything a bit more mechanical intimacy, but the problem persisted. So I came to the conclusion that the issue must be something more serious, like cracked traces or bad solder joints. This photo shows the original condition of the P82 header from the solder side:





















Close optical inspection did not reveal anything abnormal, but I was able to demonstrate that at least Pin 1 had an issue since I was able to 'disconnect' it from the component it is connected with by flexing the board a bit. So I put in a magnet wire jumper and put the board back in. After firing the Beomaster up, well, no change...o.k. I took the board back out and this time I jumpered all five solder points to their next neighbors:





















Magnet wire is really very helpful for this type of fix, since the polyurethane coating burns off when heated with the solder iron. This allows to make safe wire connections in tight spaces.

After this fix, the problem seemed to be gone. So I put the Beomaster back together...let's see if it is stable now! I usually test these babies for a few weeks until I send them back to their owners. There are just too many components and interconnections that can develop problems, and often they are intermittent. The only way to make reasonably sure that the experience on the customer end is a happy one is to give them a good testing under normal operation conditions. But I sure hope that this was the last post about this particular Beomaster 8000...;-)!

Beogram 4002 (5513): Restoration of the DC Motor - Oil Infusion of Bearings, and Repair of a Broken Off Brush and a Disconnected Sensing Coil

I recently received a package from the Netherlands containing the DC motor from a Beogram 4002 (5513). This motor tested 'dead' after I took it out of the box, so I opened it up. What I found was a broken off commutator spring, which was taped on with 'electrical tape'
No surprise that it would not turn in this condition...Further inspection yielded that also one of the sensing coils had a broken off lead (when everything is o.k. the coils have about 22 Ohms resistance between the contact terminals):
This disabled the feedback mechanism of the motor, i.e. even with intact brushes it would have spun at about 100 RPM instead of 33.33. 

This shows the motor completely disassembled with bearings taken out:
I set out to repair the damage. Luckily I was able to solder the broken brush
back together:
Then I tacked the broken off part of the coil lead back on:
The next step was to do the oil infusion of the oilite bearings. This shows the bearings the moment I put them under vacuum:
The bubbles indicate escaping air from the porous brass material, which at that moment is also replenished with motor oil. After 24 hrs the bubbling had stopped
indicating that the bearings were full with oil again. Then I put the motor back together:
and gave it a 20 hrs test with my BeoloverRPM device. The picture shows my recently redesigned enclosure, which is more practical to use and also more easily 3D printed:
This is the 20 hrs RPM performance graph that I obtained:
Most of this curve is pretty much within spec (±0.05%), but a few spikes that go to about ±0.1% are visible. Unfortunately, this seems to be pretty standard for many of the DC motors in the 551x/552x type series. It may even be an issue with the analog motor control system itself (which comes in many component variations indicating that B&O themselves were experimenting with getting these motors to run more stable). I am still working on figuring this out, which is tricky due to the intermittent nature of the phenomenon. The good news is that these variations are very small. Research shows that most people can identify pitch variations starting at about 0.7%, i.e. this is well below the detectable threshold, and therefore this Beogram will be able to deliver a satisfying listening experience once this rebuilt motor is back on the job.






Saturday, November 19, 2016

Beogram 8002: A First Look and Restoration of the PCB

Another Beogram 8002 arrived on my bench for some TLC. This one came in a disassembled state:

The hood was removed and of course the aluminum panels are detached (as usual). Under the hood, it was original
except that someone had removed the relay/DIN7 output board:
Luckily, a while ago I was able to buy a 8002 for parts, and its output board will go in here.

As usual the first step of any of my Beogram 8002/8000 restorations is to replace the electrolytic capacitors on the PCB with quality Japanese 105C grade units, and to reflow all the solder points of the board headers. Bad solder joints on this board are the main reason for operational headaches of the Beogram 8000/8002 series. Especially the connector for the transformer often has intermittent pins, causing the platter to randomly stop and other issues. I took the board out
and went to work. The most tricky part of this operation is the sole electrolytic capacitor in the 'inner sanctum', the microcontroller EMI can. It is located right next to the processor chip and serves to decouple its power supply from the rest of the Beogram:
It can be a bit tricky to remove without burning the jumper wires to the small add-on board that sits on top of the capacitor. The important thing to realize about this capacitor is that its main solder connection to ground is on the component side of the board, i.e. one has to do a bit of 'microsurgery' to unsolder it. Having three hands would be helpful here...;-). This shows the board after removal of the capacitor. The small solder pad on the left is the ground connection:
And here after installation of the new capacitor:
Once I forgot to solder the ground connection...an interesting experience...;-)

Here is an impression of the rebuilt board:
And a detail shot of the reservoir caps:
After replacing the board and plugging everything back together the Beogram showed first signs of life. Two issues were immediately apparent: It did not recognize that there was no record on the platter, and then there seems to be a missing display segment:
Interesting topics for the next few posts about this Beogram 8002! 


Beogram 4002 (5501): Installation of New Aluminum Pulley for the Carriage Servo

A few weeks ago I finished up the restoration of a Beogram 4002 (5501). The only item missing was a new aluminum pulley for the carriage servo. As usual this unit had a cracked pulley that was wobbling quite a bit, and that caused some noise and vibration when the carriage was driven fast like during start or stop. Absolutely not beolovely!

Unfortunately, the normal pulley design that Nick provides for my restorations of these Beograms does not work in the early 5501 types since they have a unique end groove detection mechanism requiring a pulley with four holes that act as optical chopper to detect the speed of the carriage. If it gets fast, and the end groove switch is activated the STOP sequence is activated and the arms travel to the home position. 

I already replaced the light bulb of this mechanism with a LED based fixture, and now I was finally able to add the proper pulley. Nick just sent me a few redesigned pulleys for the 5501 type. Here is an impression of the new pulley together with the original cracked one:
This shows it installed together with my LED based illumination setup:
And since it looks so beautiful (at least in the eyes of the Beolover...;-), here is a photo of the setup in action:
And after playing a few records with the new pulley, I am happy to report that it works very well. The holes are in the right position and they have the proper diameter to be able to trigger the end groove detection mechanism. So this baby may be close to go on its trip home back to the UK! But I will still play it a bit more to make sure that there are no intermittent issues left before it goes on its long trip.

This is what is playing right now:
And an impression from the inside of this lovely gatefold cover:
My Gabor Szabo and Chico Hamilton collection is growing rapidly. This is just amazing stuff. Cannot get enough! Must go buy more shelves for more records!...;-)





Thursday, November 17, 2016

Beomaster 8000: Repair of a Damaged In DIN7 Phono Jack That Had Lost All Four Panel Mount Tabs

One of the weak spots in Beomaster 8000s are the phono jacks in the input box under the control panel. The plastic of these jacks becomes brittle over the years, and all it takes to break out the plastic tabs that hold the jack above the input box panel is a firm push to get the DIN7 plug from a Beogram into the jack. And then the jack is inside the connector box, and the cable probably not even connected. And this is how this sorry outcome looks like:
Usually, only the top (outside) tabs break off, and there is a fix for this with two 3D printed inserts that replace these tabs. A detailed report on this repair and a video is posted here. This shows the tabs that I installed in this Beomaster:
These tab replacements are available to other enthusiasts via the Beolover Shapeways store. By the way, they also repair the jack on Beocord 8000 and 9000 units. They are also often broken out.

Unfortunately, this Beomaster's DIN7 jack posed a new challenge: It's inside tabs that hold it below the panel (so one can pull the plug without dislodging the jack) were also gone.

Since the original jacks are impossible to find these days, and even replacements from donor units are very hard to come by, I had no other recourse than trying fixing this with yet more 3D printed parts!

But first I needed to repair several disconnected leads, which probably were a casualty of a previous repair attempt. Several jumpers were broken off:
Luckily, while repairing the contact box of another Beomaster 8000 I made an extensive sketch of all the wire connections in this box, and so I was able to restore the connections without trouble:
After this I designed the replacement tab for the right side of the jack. Since it is pretty much impossible to print flexible precision parts on this size scale, I resorted to a two-pronged approach, where I first designed a static tab without spring force that would be glued onto one of the sides of the jack. This would allow to insert the jack diagonally into the cutout together with the outside tab replacements. Then, once seated, the plan was to glue another static tab into the other side of the jack from the inside of the box.

Alright, that was the plan...and here is the execution:

This shows the right side tab:
It fits into the side 'cavity' of the jack that is shown here:
This shows the part seated (with a dab of epoxy underneath):
I clamped it for an hour until I could be sure that the epoxy was fully hardened:
Then I inserted the jack together with the top tabs:
The next step was to design a tab for the other (left) side of the jack that I could get into the 'cavity' from the inside of the connector box:
I made it considerably longer than the other one. This gave me enough 'meat' to handle it on the inside and guide it into the space between jack and panel. I put some double sided tape on the contact surface and then inserted it into the space:
The part fits very snugly, and my hope is that the double sided tape will hold it in place reliably once pressed in. This will allow extracting the jack again if necessary in the future, in case there are further repairs necessary etc...I always thrive to make my repairs and updates 'reversible' in case a better solution comes along in the future.

The tight fit required me to use tongue and groove pliers adjusted to fit the task:
And this is how it looked after the repair was completed:
Almost like new! Beolovely! I gave this assembly a bunch of plug-in and -outs with a tight fitting DIN7 cable, and it seems to hold up nicely. But I will recommend to my customer to hold the jack down while pulling out the plug. Looks like we are getting close to buttoning this baby up and giving her a first spin!










Wednesday, November 16, 2016

Beomaster 8000: Step Seven - Replacement of the Speaker Switches with Modern Encapsulated Units and Laser Cut Adapter Plates

The final 'standard restoration task' for a Beomaster 8000 is to replace the speaker switches. My own personal statistics are that in about 50% of all Beomaster 8000s these switches will go bad in the near future if they are used regularly, like for headphone listening etc...They are usually corroded on the inside and frequently when a Beomaster is used again after a long period of storage, they break after a few uses and then the outputs are no longer connected to the speaker jacks. This shows the speaker switches flipped out of their 'compartments' for accessing the solder points:

Note the brown PCB-like base plates that hold the contacts...this switch style has long gone out of fashion in favor of fully encapsulated modern designs that are capable of millions of switchings before they need to be replaced. Unfortunately, these modern switches do not have this base board anymore, and hence they do not fit into the compartments under the heatsink cover. I designed laser-cut adapter plates that mimic the original base plates while snugly fitting the footprint of the modern switches:
This shows them after soldering them in:
And situated in their compartments:
All good now in switch land!

Unfortunately, when I gave this Beomaster a subsequent testing of all functions, I realized that the phono jack in the contact box was broken out and also disconnected. Very beo-unlovely! The next post will report about my repair process of these DIN7 jacks.