Beomaster 8000: Beosystem 8000 Mate to the Beogram 8000

Now that I have the Beogram 8000 turntable restored where I can enjoy it I can begin work on the Beogram's receiver. The owner of these two fine components is an original owner of a complete Beosystem 8000 set. I can gladly say I am also in the Beosystem 8000 club although the Beosystem 8000 is actually referenced as the Beolab 8000 by the Bang & Olufsen 1981 catalog. At that time the system consisted of the Beomaster 8000, Beocord 8000, Beogram 8000, Beovox MS 150 and the SC80 cabinet. When the Beogram 8002 and Beocord 9000 came out the B&O catalog called the system the Beosystem 8000.  There are actually two versions of the SC80 cabinet for the components. I have the first generation cabinet. The later cabinet has open ends instead of the closed ends my cabinet has.

I like to refer to the system as the Beosystem 8000 since B&O later reused the name Beolab 8000 for one of its powered speaker towers.

Here is the Beomaster 8000 for this next project. It is a Type 1903 and is one of the later model units.

This Beomaster is in excellent cosmetic shape although there appear to be some missing control buttons on the inner programming panel.

It looks like the button board is loose so the button covers are probably loose inside.
Here are some more pictures of the exterior before I open it up.

Beautiful. Now let's open it up. The control bar pushes down and slides to the left where it can be removed. Underneath the removed bar are the first set of screws to remove to open the receiver to its service position.

The control bar that was removed should have three brass springs to keep the bar in place. It is common for those to be missing on these Beomaster units. They are easy to fall out and get lost by technicians working on the receiver.

This Beomaster has two of the three springs.

The first one is a small spring that is all the way on the left. The other two are wider. There should be two of the spring shown in the next picture.

I have seen requests by other Beomaster 8000 owners looking for these springs so maybe it is something we can look into making a replacement part for.

Here is the Beomaster opened part way into its service position.

The metal box is the microcomputer for the Beomaster. It is the newer box design with the easy opening lid so that is nice. Here is the receiver fully opened up.

Aside from some dust everything looks really good. I have seen some Beomaster 8000 units where the boards are dark from heat. There are no signs of any excessive heat on this unit. All of the boards look great.

The door for the inner program panel is all intact and the door hinge lever is still in one piece. It is common for that lever to be broken. If that had been the case we have a Beolover 3D replacement part available.

Here  is the damping component the door lever connects to. It has damping grease inside that is often deteriorated and leaking out by now. This one appears to still be good but I will check it out more thoroughly later.

The missing button covers were indeed loose inside the board assembly. Once I removed the plastic cover they fell out. The cover has the beginnings of a slight stress fracture. It isn't bad so I will re-enforce it underneath with a flat piece of plastic and some epoxy. Perhaps the stress fracture occurred the same time the button board became loose. It is in the same area.

The Beomaster connector panel for source inputs is in good shape. All of the DIN jacks look good.

When I begin the capacitor replacement I will probably start with the hardest ones. Those are the four big reservoir capacitors for the left and right channel ±55 VDC rails.

Modern 10,000uF power supply capacitors are in a smaller footprint so I will use the Beolover 3D printed adapter for these replacements. The adapter retains the footprint of the reservoir capacitors so they fit exactly as these original capacitors do.

Time to rest up before starting the recap work.

Beomaster 8000: Reservoir Capacitor Replacement

I have all of the Beomaster 8000 restoration parts in hand now. The first step for me is to replace the electrolytic capacitors that are the most difficult to get to. Those are the four 10,000uF reservoir capacitors in the back. It takes the most disassembly to get to them so doing them first will get that out of the way.

Modern electrolytic capacitors of the same capacitance and voltage rating are often smaller in size than when this Beomaster was made (early 1980's). That means finding some filler for the capacitor cavity in the Beomaster chassis where the reservoir capacitors mount. Fortunately Beolover has solved that problem by designing 3D printed capacitor sleeves that allow modern replacement capacitors to be mounted as the original component.

Here is a photo of the four Beomaster 8000 reservoir capacitor assemblies I ordered from Beolover.com. This is my first time using these parts and they are very nice.

Here is the Beomaster 8000 with its original reservoir capacitors. As you can see they cannot easily be disconnected and removed. They must be de-soldered and care must be taken in doing that.

To get my de-soldering gun and soldering iron to the capacitor terminals so I can remove the wires I removed the back plate of the Beomaster chassis.

With the back panel off it makes de-soldering and removal of the capacitors easier as well as allowing some cleaning of built up dust around the big transformer.

Here are the new Beolover replacement capacitors soldered in place.

Finally, here is the Beomaster with the new reservoir capacitors installed and the rear chassis re-assembled.

The next step will be to recap the power supply board followed by the two output amplifier boards. Then I will do a test to make sure the power is functioning.

Beomaster 8000 Output Transistor Replacement

Today I checked out the output stages of my 4th Beomaster 8000. The blown fuse indicated some trouble there. Indeed a visual inspection of the two output amps revealed two darkened R236/7 power resistors, a telltale sign that the output burned out at some point. The right channel seemed to look pristine. I removed the heat sinks with the output transistors.

To make sure I used my multimeter to measure the resistances in the 6 output transistors of both channels.

On the right I measured high resistance values (several 100k) in the emitter-collector circuit, while on the left the resistance was less than 1 Ohm, indicating a full short circuit between the power rails.

Next I rebuilt the left output board with new electrolytic caps and a 11 turn 100Ohm trimmer for the quiet current adjustment (see post http://beolover.blogspot.com/2011/09/output-stages-testrecap.html for details on this procedure). Then I replaced the 6 output transistors (3x TIP141 and 3x TIP146). This is one of the more painful Beomaster 8000 repair procedures since one needs to extract the old transistors and then squeeze the new ones in under the springs with some heat sink compound, which always turns into a mess. I recommend to use vinyl gloves for that. Here are the dead transistors after extraction:

Interesting to see that they were made in Italy...the good old days. The new ones that went in were from Malaysia.
The next step was firing up the left channel with bench power supplies (see again http://beolover.blogspot.com/2011/09/output-stages-testrecap.html for details). By the way, there is no problem with first turning up the +15V supply, and then slowly ramping the ±54 supplies to their max voltage, while watching the current (I usually keep the current limiters on the supplies close to turnoff to make sure that nothing adverse happens during this test)

The currents into the board (at 18mV across R236/7) were a bit higher this time:

+54V ---> 0.15amp
-54V --->0.16 amp
+15V ---> smaller than 0.01amp

Not sure why this difference...at any rate it seems the output is working again properly. After 30min the temperature on the heat sink was just slightly above ambient...like it should be.

Beomaster 8000 Back Together!

After an uneventful recap of the tuner section (boards 1&2) I put everything back together. Here is a pic of the finished boards:

Testing revealed no further issues except the missing display segment...I will take care of that soon. But first I need to practice how to solder SMD LEDs....