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.

Beomaster 8000: Display Repair (III) - Putting the Displays Back Together

The SMD LEDs in the displays of the Beomaster 8000 survived the 24hrs stress test. So I put the displays back together. To date I always did this by glueing small pieces of transparency foil to the remaining 'stumps' of the red plastic cover, sort of trying to recreate the original situation where these plastic tabs were just melted a bit to seal the covers in place. See this link for more details. 

I did not really like this approach since it made it difficult to get back into the displays if there would be an issue down the road due to the bleeding out superglue under the plastic pieces.

The Amateur's mess with the frequency display inspired me to try a new solution. When he re-assembled the display he used a glue gun to glue the displays back together. When I took this display apart, I was impressed how cleanly the glue came off by giving it a hard peel without doing much damage to the red cover nor the PCB underneath.

I took this page from Mr. Amateur's playbook, but improved it by a more precise application, and by using a black glue stick. This has the nice side effect that any LED light that wants to sneak out from underneath the mask/red cover will also be blocked. I only applied the glue on the sides, and used black tape to mask the front and the back to ensure darkness (the most critical spot is the stand-by LED, since it is glowing when the receiver is off, i.e. any trickling out light is easily visible in a dark room as a halo in front of the display... Anyway, here are a few pictures of the process:

Black tape applied to front of volume display mask:

Clamped display with a strip of black glue applied. A solid strip like this can be peeled off in one piece with some effort (and strong fingernails...;-). This is a pretty strong bond, but completely reversible. I like reversibility, since one never knows what will happen down the road...

Full assembled volume display:

and back in the test fixture to see if all LEDs survived the stress of clamping etc...

Time to put the displays back in...just received the 68 Ohm resistors today to reverse Mr. Amateur's attempt to reduce the intensity of his SMD LEDs. More about this in the near future...

Beomaster 8000: Display Repair (II) - Installation of SMD LEDs and Test

After cleaning up the mess with the frequency display of the Beomaster 8000 that I am restoring right now, I went ahead and opened all displays and scratched off the old LEDs with a carpenter's knife. One needs to be careful when doing this since it is very easy to damage the traces with the knife edge. Here is a picture of the naked boards:

Now it was time to solder the SMD LEDs onto the pads. I am using LUMEX SML-LX0603IW-TR types. When doing this it is very important to remember that the LEDs need to fit under the masks that shape their light into the elongated 'segments' that make up the 7-segment displays. This requires precision soldering and a steady hand to make sure that the small 0603 parts are fully centered on the pads. Otherwise the mask will be obstructed and a gap results between the mask and the PCB that permits light out of the sides of the display. This results in an unwanted 'halo' around the displays that can be seen very well when the Beomaster is operated in a low-light environment.

For soldering I always line up the LEDs in same orientation in rows, so I can pick and place them efficiently:

Here is a picture of the frequency display after installing the LEDs:

And lit:

And here a picture of all of the displays in my test fixture:

Once I solder in the LEDs I usually run them for 24 hrs to make sure that there are no issues. Tomorrow, if this goes well, it will be time to close them up and re-install them on the display PCB.

Beomaster 8000: Display Repair (I) - Cleanup of Botched Frequency Display

Before going further with this Beomaster 8000, I wanted to make sure that the frequency display would be salvageable. So I took the displays out today and had a look:

Display PCB (#9) after removal from the Beomaster:

Displays removed:

Here a picture of the frequency display after I opened it up. A beautifully messed up SMD soldering job! A true expert was at work! (actually, I have to admit this does remind me of my first attempts...;-). Unfortunately, I damaged a couple traces when I cut the glue off that Mr. Amateur used to put the display back together:

My rework station made it an easy job to clean this mess up. I also soldered small copper braid snippets into place where I damaged the traces. So, I am confident that this display can be rebuilt:

Upon further inspection of PCB #9 it became apparent that Mr. Amateur also tampered with the current limiting resistors since he probably noticed that his display was a bit too bright. Here a couple pictures of his work:

Shudder - What a mess!:

He should have practiced a bit before getting into this! I ordered a few proper 68 Ohm resistors from Newark to replace his 100 Ohm values. Soon this will all be back to normal (except a few minor scars...;-).