Beomaster 8000: Display Board (part 2)

I completed installing the new SMD LEDs in the remaining three Beomaster 8000 display modules. It was pretty much the same as with the first display module except a lot more LEDs to solder. The job is quite tiring on the eyes.

If you are looking at refurbishing your own display modules I can tell you that the best method I have found is to solder one side of the SMD LED first, then check the fit of the display light guide. Last year I tried using an SMD work station that has a hot air gun and a board heater along with SMD solder paste. Unfortunately the solder pads on these display board are too wide and the hot air gun would blow the SMD LEDs out of alignment (but still on the solder pad).

The result was a lot of rework by hand so it is better to just do the LED soldering manually to begin with. One side first, a fit check and finally the other side. Tedious for sure but the displays work the first time this way.

I started with the largest display module, the FM channel display and worked my way down to the volume level display. Here is the FM channel display  beginning its testing.

Here are all four displays powered up on the test jig.

I will let them burn-in for twenty-four hours before I seal up the modules for re-installation on the Beomaster display board.

Once the displays are back on the display board it will be time to reassemble all of the refurbished boards in the Beomaster 8000 chassis and try this restored receiver out.

Beomaster 8000: Display Board (part 1)

The last remaining board to work on is the display board. I guess I saved the easiest board to remove for the end. It only has two capacitors to replace so it should also be the easiest board to work on. However, the digital displays on this board often begin to have faulty LED segments after thirty five years. On the capacitor replacement we replace all of the electrolytic capacitors regardless if one still measures in spec. The reason for that is we know they can and likely will fail. The same reasoning goes for these displays.

Here is the display board for this Beomaster prior to the restoration.

I removed the four segmented display modules as those are the components with the LEDs that eventually start to fail.

There are also four incandescent bulbs (Clipping, Filters, Mono, Manual tuning) that will get replaced with Beolover LED replacement modules.

Here are the two electrolytic capacitors replaced (a 10uF and a 4.7uF).

Here are the before and after pictures of the incandescent lamp replacement.

Note that four 220Ω resistors (R34, R36, R38 and R40) are removed from the board.

The most time consuming task on this whole Beomaster 8000 project is the replacement of the LED displays. Since several Bang & Olufsen components from this early eighties time period use this type of display I made a test jig for bench testing them.

I always check whether any segments have started to fail or not.  It turns out all of the display segments are still functioning on this Beomaster.

Very nice and a key design element to these Beomaster units. However, we would really like to insure that this Beomaster doesn't have to come back to the shop in a year or two if these old display segments finally start to give out.

Changing out the original LEDs with modern SMD LEDs is a tedious task and I need to get back in the mode of working them so I will start with the smallest display module first...the channel balance display.

Here is that display with the red lens cover removed. You can see the tiny LED components in the display guide slots. Lining up the replacements in those slots is important.

Here is a further breakdown of the channel balance display. The display guide is now removed to better reveal the original LED components.

Those LED components are quite a challenge for eyes as old as mine. It's a good thing I have plenty of magnifying tools to help me.

Here is a closer look at the original LED component compared to its modern replacement.

For more detail on these displays you can check out an earlier Beolover Blog of a Beomaster 8000 project I did last year.

I soldered in three of the eleven new LEDs then did a quick test to check the work. So far so good.

After completing the replacement of the other eight LEDs on this lamp module I put it back on the jig for an overnight burn-in test.

The light guide fits perfectly over the new LEDs.

...and here is the lens cover snapped back on. After the burn-in test I will seal this module up better.

Three more display modules to go.

Beomaster 6000 (2702) restoration: electronic switch and motor operation board

The Beomaster 6000 quad contains 2 important boards with a whole range of micro switches that are activated by the steel "tongues" on the front panel. They are not the touch-sensitive controls (like on the Bemaster 1900 than came out a little bit later), but pure mechanical contacts with a tiny air-gap of 0,5 mm. Therefore everything needs to be carefully aligned, cleaned and checked if you want to avoid that the user needs to push hard on the key-panel to activate a control. 

So, these 2 boards are recapped, contacts cleaned and all glass bulbs replaced (12V - 30mA plug in type, but with wires pulled out). Again a fiber pen and Deoxit GOLD was used for the contacts.

Cleaning the contact bridges

When resoldering the contact bridges it is important that they are fully pressed in the board to get the required 0,5 mm air gap.

All contacts cleaned !

Time now to turn the board and replace all the glass bulbs

The same thing for the smaller motor operation board. Just cleaning of contacts. No recapping or glass bulb replacement.

Shiny and bright ! Up to the next phase...!

Bemaster 6000 (2702) restoration: the FM preset board

Restoring equipment also requires cleaning. After 40+ years, some units collect dust, a lot of dust as you could see already in one of my first posts "a look inside". The FM preset board was no different. A lot of dust but also corroded trimmer contacts. These trimmers are open types and the board sits just under the front key pannel where you have a lot of "gaps" where dust can penetrate. 

One needs to desolder the 3 trimmer contacts to be able to remove and open them. After desoldering they slide out of the main black plastic holder.

Once you get them out, it is easy to disassemble them. A small retainer clip on the back needs to be removed and then everything "falls apart".

Time to remove the old grease and clean up the carbon and slider contacts. I used a fiber pen and Deoxit GOLD cleaning & coating.

After reassembling I continued with the remaining 4 and cleaned them the same way.

The only thing left now was to solder them back on the board. Important is to make sure they are all pressed completely against the board for perfect alignment before soldering.

Looks good to me ! 

Beomaster 6000 (2702) restoration: ultrasonic receiver and tone amplifier

Another PCB where everything is very tight and space is limited: "PCB 14, remote control receiver". Luckily not that many capacitors but also a few trimmers that I wanted to replace. And there I found again something interesting: the trimmers only had 2 legs ! The slider contact that typically sits in the middle, was here one of the two outer contacts. Never seen this before. So I had to modify the multi turn trimmers that I wanted to use. Not a big issue however.

The added advantage of using this type of multi turn trimmer on this PCB is that it is now reachable from the top and does allow setting without removing the PCB. This was not the case with the original trimmers.

Recapping the tone amplifier was pretty straight forward. All easy reachable capacitors. As you can see, this board is still attached tot the potentiometers (the string of coloured wires).  I did not want to unsolder all those wires unnecessarily . 

Beomaster 6000 (2702) restoration: recapping level amplifier with SQ decoder and pre-amplifier

When restoring vintage audio equipment it is good practice to replace all electrolyte and tantalum capacitors. Today the level and pre-amplifier PCB's are done as well as the small PCB for the SQ decoder that plugs into the level amplifier. This was done to allow further upgrade to new quadrophonic (de)coding systems. There was no standard yet in the mid seventies and in fact there really never came a standard! During those days about a dozen systems existed. Some for records, some specific for tape: SQ, CD-4 (used in the Beogram 6000), QS, DY, EV, UD-4, Quad-8, Q4 (the very first - invented in the fifties), etc. None was really successful and all where abandoned a decade or so later.

Today we would probably call this quadro systems: 4.0 surround sound !

Anyhow, back to the recapping. When replacing capacitors it is obvious that the value and voltage rating is crucial and need to match. Sometimes two or more capacitors need to be combined (in series or parallel) to match the old one. It is common in speaker crossovers for example to see odd values that are no longer industry standard.

But dealing with recapping of PCB's in this Beomaster 6000 quad poses another challenge: box size ! On the pre and level amplifier there are more than 60 capacitors and mostly tantalum. They where chosen for the small size compared to the aluminium electrolytes for the same values (today electrolytes are a lot smaller than back in those days). But even today, when replacing those tiny tantalum's, it is often impossible to go for electrolytes because they simply don't fit in the space. The WIMA MKS foil capacitors are the best choice for me. But even then, one needs to be very careful what type is chosen. Don't go to high in max voltage rating, check the different box sizes between the different PCM measures (2,5 or 5mm distance between the leads). Some are square, some are rectangle. Many of the MKS (polyester film types) that I had in stock did not fit. 

This is for example the level amplifier before recapping

And after recapping

And the SQ decoder that fits in the black plug in the above PCB

The pre-amplifier was even more challenging

Only a few boards left now for recapping. But that is for a next post...

Beomaster 8000: Microcomputer Board

Time for the Beomaster 8000 microcomputer board work.
Here is the board removed from the Beomaster.

The components I am interested in are inside the metal shielding box. This board has improved for the better from earlier serial number Beomaster 8000 units. The original metal boxes were soldered shut and a real pain to open up. It was very easy for the circuit board to get damaged when de-soldering and opening up the box. I have seen several units with copper pads torn from the board. This newer shield box has snap on lids for the top and bottom sides. Very easy and much appreciated.

There are just two capacitors that will be replaced as part of the Beomaster recapping effort. A 1uF tantalum and a 22uF electrolytic. You can see on the 22uF electrolytic and some other nearby components that this board has some solder point vias where both the underside (trace side) and component side must be soldered.

Part of this restoration is to reflow solder for the vias and board connectors.

Another update on this microcomputer board will be to change out the crystal oscillators for the two processor chips. The reason for this is that we have seen some cases where those components begin to fail so we go ahead and change them now. Here is a previous Beolover Beomaster 8000 restoration where we first encountered problems with the oscillators. Better to be safe than sorry.

Changing the crystal oscillators means changing four ceramic capacitors (two for each oscillator). The capacitance of those capacitors is defined by the crystal oscillator device. The new replacement 2MHz oscillators call for two 18pF capacitors so that is what I am using.

This picture shows the original oscillator components that will be replaced. Per the information on the earlier Beolover post I shorted the oscillator leads and removed the two microcomputer ICs (wearing proper anti-static protection of course).  Having the microcomputer ICs out of the way is a safety step to avoid any damage to the chips.

And here are the replaced components. The new crystal oscillators are much smaller. The original components were secured by some double-sided tape. I removed the old tape and used some Aleene's Tacky Glue.

Here is the completed microcomputer board before putting the shield box lids back on.
Note that the oscillator leads were again shorted together for the reinstallation of the microcomputer chips in their sockets.

Now it is on to the Beomaster 8000 display board.