Beomaster 8000: First Look Inside

It seems the last Beomaster 8000 is now happy, and I put it back together. It went to the living room for a few weeks of testing amongst his friends the Beogram 8000 and the Beocord 9000.
Time to open up the next 8000 in line! This one is very nice on the outside, and the interior is not different. While it was opened up before (slight screwdriver mark on the glass cover - still have to see an 8000 without...it is definitely a good idea to protect this corner with some tape before opening them up...). There is also an about 15 year old cap in there (6C35 to control the 5V ripple after the voltage regulator). But whoever did it put it back together properly...all screws the right sizes, nothing missing, even the small copper damper for the control panel door release is in its proper place.

Otherwise, it is as original as it gets upon visual inspection. Also very clean. Almost no dust! Very nice! Check out this left channel output board: Almost as it were recently put in a cleaning bath:

But, appropriate for the age, two of the red electrolytic caps are cracked, indicating that a full recap is probably a good idea. The output resistors are non-browned, which makes me hopeful that it really still worked as it was advertised on ebay.

The displays are unfortunately pre-solder mask style, as is evident from the whitish epoxy boards:

We will see how the segments are when I turn it on the first time. Experience tells me that this style displays is prone to segment failure. It seems that displays with the greenish epoxy boards may be more stable over time.

Next step: As usual, I will rebuild and test the output stages before the first turn on.

Beomaster 8000: 3D Printed Control Panel Linkage

This is the continuation of an earlier blog entry at http://beolover.blogspot.com/2014/06/beomaster-8000-3d-printed-controls-lid.html

I started reassembling the recently recapped Beomaster 8000. It was time to try out the 3D printed control panel cover linkage that I had printed a few weeks ago after finding that the original linkage had cracked and lost one of its hooks. 

I put in the 3D printed part (Makerbot II, PLA, highest density), and it worked nicely - for a few openings and closings - then it popped out at the damper. This meant that my part had a slightly too wide gap on that end, which would allow the damper arm to come loose. I redesigned the part in Inventor with a 0.2 mm smaller gap, and had it printed again. This time it worked very well. The part clicked in solidly, almost too tight. I lubricated it with Ballistol, which resulted in very smooth operation. 

I made a short YouTube video that gives some more info and shows the part installed and in action:

The STL file for the linkage is posted on my website at beolover.com:(http://beolover.weebly.com/control-panel-cover-linkage.html).

Beomaster 8000: PCB 1 and 2 (Tuner) Recapping

Today was Tuner Day of the current Beomaster 8000 restoration project. The tuner worked basically fine, but there was an intermittency on the right channel, seemingly depending on the moon phase...;-). Tracing the signal with the oscilloscope, revealed immediately that one of the contacts in plug P6 was poor. I pulled the boards apart (they come out together...), and cleaned the contacts with a fiberglass pen and bent them a bit for added contact pressure. Then I added a coat of DeoxIT D100. As usual, this seemed to do the trick. Wiggling the boards did not cause problems in the right channel anymore! Here is a pic of the contacts before cleaning...some black oxide spots are clearly visible where the female headers made contact:

Such black spots come easily off when using a fiberglass pen on them. I forgot to take a picture, but one can achieve as-new looks that way. The DeoxIT further cleans the contacts and provides a protective layer against future oxidation.

While the boards were out, I also recapped them with quality 105C caps. An uneventful procedure. Here is a picture of the boards before the procedure:

And after:

And a detail shot of the region around the IF stage (CA3189E):

Well, almost done!! On to the preamp board (PCB #3)...

Beomaster 8000: Rebuilding the Filter and Tone Controls Board (PCB #4)

Today I took the filter and tone controls PCB of the Beomaster 8000 out and replaced the capacitors. This required unsoldering the signal strength meter leads from the PCB, and unscrewing the plastic panel that holds the switches, buttons and sliders. Here is a pic from the bottom of the PCB before taking it out:

The meter in the lower left corner needs to be unsoldered to be able to remove the PCB from the plastic cover. Five screws hold the PCB to the plastic cover. It is important that these screws do not get tightened too much when re-installing the board. The plastic standoffs can easily crack.

Here is a photo of the meter after unsoldering the leads:

This is a pic of the board after removing it before replacing the capacitors:

And with new caps:

Several of them needed to be tilted to accommodate for the low clearance between the plastic cover and the board. This PCB also had one cracked ceramic capacitor (C207).

I replaced it with a new 10nF type:

After screwing the plastic cover back on (it is a bit difficult to get all the buttons and sliders slotted at the same time - patience helps...;-) I soldered the meter leads back onto the board, and tested the Beomaster...seems all works fine. On to the tuner boards.

Beomaster 8000: Replacing the Speaker Switches

Time for the Beomaster 8000 speaker switches while the heat sink cover is off. Another 'standard rebuilding task'. These switches are corroded in most 8000 units, and when used consistently will fail soon. I often switch between headphone and normal speaker operation, and these switches failed in all three of my personal 8000s after a few dozens switchings. Hence, they must go. Luckily, there are almost identically looking modern encapsulated replacements available. See here for more details on part numbers etc...:

http://beolover.blogspot.com/2011/10/beomaster-8000-speaker-switch-repair.html

I used pretty much the same procedure in the current restoration project, except that I directly drilled holes into the base plates, instead of messing with the Dremel tool...can't beat experience! Here are some pics:

Original switches from bottom:

After I removed the bottom plates from the old switches and drilled holes into them to permit the pins of the new switches to protrude:

After glueing them together. This establishes the original form factor that they fit into their compartments:

After soldering them in:

And in their compartments: Like it never happened...;-)!

The control panel is next! Slightly dicey affair due to the often cracked plastic receptacles for the screws, and the buttons and sliders that need to be refitted in their proper places during re-assembly. I always wish I had four hands to do that!

Beomaster 8000: 3D Printed Controls Lid Linkage

I just received a 3D printed part for the Beomaster 8000 I am currently restoring. When it arrived I pressed "Programming" to access the controls, and the brushed aluminum cover popped open at an alarming speed, indicating that the damper was disconnected. Once opened the Beomaster up, this was confirmed. Sadly the plexiglass link lost its bottom end and therefore lost contact to the damper that prevents the cover from snapping open. Here is a picture of this sad state of affairs:

So I recently drew up this part in Autodesk Inventor, guesstimating the missing bottom end (I didn't have another 8000 open at that point to take measurements of a complete part). Then I had it 3D printed on a Makerbot II using black PLA: Here is the result:

I designed the holes a bit smaller, and then drilled them out with a 9/64 (right, lid) and a 11/64 (left, damper end) bit. The Makerbot has a hard time to get hole dimensions perfect on this size scale, and it is better to drill the material carefully to get a more machined feel for rotating joints like in this case.

I tested the part on the damper and the lid joints, and it seems to click into place fairly well...when I assemble the Beomaster again, we will see if this really worked (I am a bit concerned that it might disconnect from a joint when using the cover in a routine fashion - I will post an update on that).

Anyway,my fun with 3D printing continues!

Beomaster 8000: Replacing the Reservoir Capacitors

Today was the day for the reservoir capacitors of the Beomaster 8000 on my bench. Always a pleasure to replace these big 10000 uF cans! After all it all begins with them! I replaced them with the 105C ECES1JA103EZ Panasonic type. They have almost the same size (35 mm diameter vs. original ones at 40 mm and same 80 mm height) and clock in with a solid ESR of 10-11 mOhm at 100Hz for an unimpeded flow of power. They are also rated for 105C, i.e. promise to last for a while, even if it gets a bit warm back there. Unfortunately, this type was discontinued not too long ago...it is getting difficult to find this form factor...electronics parts continue to get smaller. The 5 mm diameter difference was corrected with a wrap of thin corrugated cardboard. That way they fit snugly in their compartments.

Here are some pictures:

Before:

Pretty dusty back there...(sorry for the slight blur...)

And after replacing them:

Almost sexy!!...if you know what I mean...;-)

And here a detail shot of the left channel:

On to the speaker switches, while the heat sink cover is off...