Beomaster 8000: Recapping the Preamplifier and FM Tuner PCBs

I continued the recap of the current Beomaster 8000 restoration project. Yesterday, I did the preamplifier and FM tuner PCBs. Not much spectacular to report, just a bunch of new 105C grade Japanese capacitors replacing the aged and partially cracked 1980s types. Here are a few impressions:

Preamplifier board before:

And after replacement of the capacitors:

And a detail shot:

Tuner PCBs before:

And after. It is important to clean the contacts between the boards. I always coat them also with some DeoxIT D100 to prevent further oxidation down the road. If one does not do this there is a good chance that the tuner may tune out on one or both channels since the signals travel through these connectors. This picture shows the boards after the recap:

And a detail shot:

On to the filter and tone control board, the last PCB that needs new capacitors. Then it will be time to put the Beomaster back together and test the 3D printed latch! Exciting!

Beomaster 8000: Replacing the 10mF Reservoir Caps

After doing the speaker switches of the Beomaster 8000, the logical progression is to replace the main reservoir capacitors for the output stages. These 10000uF capacitors often loose part of their capacitance at this age, which causes ripple in the power supply and limits the responsiveness of the outputs during loud impulses. Since new capacitors tend to be considerably smaller, I use 3D printed adapters (on a Makerbot II) for the new 105C types:

At this stage the Beomaster is typically completely opened up:

This are the original capacitors of the right channel:

And after replacement with the new ones:

And here the left channel:

And after installing the new ones:

After I was done I measured the old capacitors, and found that two of them had very low (~2.4mF) capacitance values, definitely out of spec:

I expected this since their tops look slightly bulged, usually a sign for trouble.

The remaining tasks with this Beomaster are recapping the preamp, filter and tone control and the two FM boards, and then fixing the latch of the control panel cover. I am curious how this will turn out...I just received the 3D printed replacement parts for the maimed latch this Beomaster came with, but I can only try the parts out, after I put the Beomaster back together. We will see soon!

Beomaster 8000: Replacement of Speaker Switches with New Encapsulated Ones

Today I opened up the back of the Beomaster 8000 to replace the speaker switches and then do the big reservoir capacitors for the outputs. Replacement of the speaker switches with modern ones requires the use of adapter plates since the original switches are no longer available. Last year I designed suitable adapter plates that can be laser cut. I made a short video about the entire process. It can be found here. I improved the design in the meantime by thinning the far ends of the plates using laser raster scanning. That ablates the plates to a perfect height and they fit a bit better into the compartments when the heat sink cover is installed. Here is a picture of the new switches with plates in comparison with one of the old switches:

The following pictures are from the exchange procedure:

Old switches from top:

and from bottom. The old PCB style bottom plates are visible. The compartments are designed to fit them. They need to be replaced by the laser cut adapters:

The new switches after soldering them in:

And after seating them in their compartments. A perfect fit! This is Beolove...;-)!

On to the reservoir caps while we are back in there!

Beogram 4002 (5513): First Contact and Test Drive

I recently received a nice condition Beogram 4002 (5513) for some TLC. So I opened it up and hooked it up to my Beosystem 6000 for a test drive. Immediately when I turned on the Beomaster 6000, a loud hum became apparent...I turned off and had a closer look. It turned out that P9 on PCB was inserted 180 degree reversed. That can happen since the 6 pin plug is not polarized, i.e. it can be inserted in both directions. Luckily, this is not damaging, since this plug does not carry any power rails. Here is a picture of the wrong orientation:

According to the circuit diagram the black chassis ground lead needs to be on the right side when observed from the front of the turntable. Like so:

This fixed the hum issue.

Further inspection also revealed a bit of a messy (but inconsequential) soldering job at the chassis GND connector at the back of the Beogram (I really wish people would spend a few minutes watching some of Norman Meir's absolutely excellent soldering tutorials on YouTube before messing with these beautiful vintage units...;-):

So far so good! I am listening to Somethin' Else (Blue Note 1595) on a nice 200g Classic Records audiophile reissue (stereo version) trying out the lovely, nice condition MMC6000 that this Beogram has fitted! Lucky owner!!

Beomaster 8000: Rebuilding the Power Supply Board and an Inspection of the uProcessor PCB

After the display PCB of the Beomaster 8000 was happy again, I focused on getting the basics on a sound footing. This means doing the processor board upgrade and a full recap of the power supply. So I started with the power supply PCB and replaced all electrolytic capacitors with 105C-grade capacitors from main Japanese manufacturers. Here are a few photos:

Power supply PCB extracted before recapping:

After recapping:

And installed:

After this was settled, I looked into the shielded microcontroller compartment to look into the B&O recommended upgrades. This is what I found:

It is obvious that this board came already with the jumper wires installed. These serve to bridge the often problematic vias, which are the main cause of operational inconstancies such as sudden stand-by or turn off of the output stages. Therefore, all I needed to do was to replace the two decoupling capacitors on this board. Here is a picture after putting the new caps in:

Next step is to open up the heat sink cover and replace the speaker switches and the four 10mF output reservoir capacitors...they seem to bulge a bit, a sure sign that they are about to go.

Beomaster 8000: Replacement of Indicator Light Bulbs with LEDs

Today I finished rebuilding the display PCB of the Beomaster 8000. After fixing the displays, what remained was to replace the incandescent light bulbs of the four indicators with red LEDs. When I did that the last time, I made a short video discussing the procedure. When I removed the old bulbs, the leads of two of them broke off very easily. I saw this before. It seems that these bulbs die mainly by losing their corroded leads at the point where they are fed through the glass, instead of burning out their filament. Here are a few pictures:

Original light bulbs:

LED replacements. One needs to use two LEDs and a 47 Ohm current limiting resistor:

The two indicator sets need mirrored LED setups to fit the bulb solder pads:

After installation and removal of resistors R34/36/38/40 (otherwise the LEDs will faintly glow if they are in off condition - see video for a discussion):

And in action (the clipping LEDs are off...):

And with covers replaced:

On to the power supply...

Beomaster 8000: Display Repair (IV) - Display Back in Business

After another 24h test of the assembled displays I put them back on PCB#9 of the Beomaster 8000. Before soldering the displays back in, I also exchanged 9R14 and 9R16 with 3.3k and 1.5k resistors:

This reduces the display voltage and allows to reduce the intensity of the SMD LEDs to the original brightness level with R15. One needs to be careful when adjusting trimmer R15, it should not drop the keyboard strobe below 3.2V. Otherwise the keyboard will start getting erratic. More detail about this procedure is posted here.

After the displays were back in and tested o.k. I started remedying the mess Mr. Amateur created with the current limiting resistors and adjacent jumpers. No idea why he needed to mess with these jumpers, too...but he did a great job destroying the solder pads. I soldered bridging jumpers in that bypass the disaster area altogether. I was able to salvage the pads of two jumpers and replaced the jumpers with new wire.

Here are some pictures before:

And after:

Much prettier now, I'd say...;-). After this surgery, the displays all showed the same intensity again. All good now in display land. While I listened a bit to the radio, I realized that one of the speaker switches is intermittent on the right channel...so these need to be replaced, too. This is a standard restoration task, it seems they are often corroded.