Beomaster 2400 Type 2902: Reassembly and new display masks

The Beomaster 2400 has been playing music again in my workshop and I haven't even finished reassembling it.  To complete the reassembly I need new display masks for the tone controls (bass, treble and balance position indication).  Those parts are no longer available from Bang & Olufsen so I have to make replacements. I have done that before on the Beomaster 1900.

Here is the Beomaster 2400 with just the new bass display mask remaining to reinstall. The treble and balance indicator masks are already in place.

Interestingly this Beomaster 2400 serial number uses the same display mask pattern as the Beomaster 1900 units. That is interesting because on later serial number Beomaster 2400 units, but the same type: T2902, the mask pattern changed.

Here is the later mask pattern next to the one this Beomaster came with.

The early mask pattern used a clear square to indicate the current control position with vertical lines displayed on either side. The later pattern blacked out everything except the selected position which now has vertical lines. I guess they had a lot of discussion in the design department over which pattern they liked :-).

It is hard to capture the detail of the display masks but I was able to change the speed and sensitivity on the camera to get this close up of the new masks installed.

With the display indicator masks back in place I could reinstall the back plate and tone control deck.

As with a lot of the Beomaster 1900 and 2400 units this one arrived at the shop with missing and broken feet. Luckily that is another part supplied by Martin Olsen and I installed four new feet on this Beomaster.

The Beomaster is now ready for functional testing. I will start that a little later. For now I will leave the receiver playing an FM station as part of my ongoing burn-in testing.

It looks great and sounds great...and I haven't finished cleaning and polishing the cabinet yet.

Canada Beomaster 8000: Rebuilding the displays

I have the new smd LED components installed in the Beomaster 8000 segmented display boards and I am running a burn-in test on them.

It is a little difficult to capture (in a photo) what the rebuilt displays look like without the top lens cover on but the purpose of this test is to make sure all of the segments work. I usually run this burn-in test for twenty-four hours. That gives the new components a decent amount of time to fail if they are going to. I would hate to bundle everything up then have to disassemble the displays again.

To get to this point I removed the display modules from the Beomaster 8000 display board.

There are white and red tabs on the rear of the display board modules that hold the light guide and lens cover in place. Those tabs were originally part of the plastic sub-assemblies and melted down to secure the full display assembly. Since those cannot be removed and reused I have to just cut them off and use a different way to re-assemble the display modules after I rebuild them.

Here is the channel balance display board with the light guide and lens cover removed.

You can see these Bang & Olufsen display modules were very custom and the tiny, smd-like LED components cannot be replaced. We could locate the LEDs that have failed and just change those. However, that would result in a noticeable difference in the red illumination because the new smd LEDs are not exactly the same as the originals. They are very close but not the same. So it is best to change all of them. Another equally good reason to change all of the LEDs is because you can bet that if you only changed the failed LEDs the remaining good ones will likely fail as well. It's definitely better to get everything done while the Beomaster is open.

Here are some pictures from previous Beomaster 8000 display repairs that I use as a reference for this task.

This first picture shows the new smd LED component next to the original B&O LED.

This picture shows identifier markings on the replacement smd LED component for reference.

The next step in the display rebuild after removing the light guide and lens cover is to cut out the original LED component.

I gathered a number of my Bang & Olufsen display modules that I have been wanting to rebuild and hope I can take the opportunity, while I am display repair mode, to get them done as well.

To prepare each display board for the new smd LED components I cut off the small solder pad that the original LED cathode rested on. That makes the gap between the anode and cathode pads better for the new components.

It is important to "tin" the solder pads before mounting the smd LED components. That will ensure a good, reliable connection.

Now for the actual mounting of the new smd LED components.

I have to say that this task is one of the most time consuming restoration tasks and requires a lot of patience to handle the smd LED devices while soldering them in place. The technique I use (and recommend) is to mount the smd LED components just on one lead. The reason is because the LED component must fit just right in the plastic light guide of the display module. There are always several LED components that I have to reposition slightly to correctly function inside the light guide. That also means the soldering process is to first position the smd LED with tweezers, solder one side to secure it, check the fit with the light guide, reposition if necessary and finally, solder in the other side. Quite labor intensive and hard on the eyes.

Here is a fit check of the smd LED in the light guide.

Once all of the new LED components have been fit checked I finish soldering the LEDs to the board.

Here is the completed FM tuner frequency display board.

On to the remaining three modules.

Another tip is to have a reference picture or (even better) a spare display board to use as a reference when mounting the new LED components. This task is very tedious so be disciplined to check the polarity carefully with each LED mounting.  It is also another good reason to only solder one side initially.

Here is the completed LED replacement on the Beomaster 8000 selected source display board.
Note: The glare from my lighting off the no-clean flux residue makes a couple of the solder connects appear shorted.

The volume level display board is next.

Finally the channel balance display board. This board is the easiest to position the smd LED components on because it doesn't have pads where the LED mounts. However, the narrow trace makes soldering in the LED components a little tricky and this board is usually the one to have a connection problem.

Once the twenty-four hour burn-in test is complete I can reassemble the four display components and wrap up the display board. Then it will on to functional testing with this Beomaster.

Beomaster 4400 (2419): 30 Hour 60dB Test

Functional testing update...
Because of the earlier incident with the left channel 5R173 and 5R174 resistor failures I am putting this Beomaster through extra long burn-in testing.

Over the weekend this receiver successfully played continuously for thirty hours at a volume level that produced 60dB to 65dB of sound out of my Beovox S55 speakers (measured from 15 feet away).
The output transistors on the heat sinks measured around 100°F to 120°F at various times during the thirty hour test.

The testing continues.

Beomaster 8000: Display Board Burn-In Test In Progress

I have been enjoying playing music through this latest Beomaster 8000 unit as I check out the work I have done on it so far. This is always a satisfying and enjoyable time in a project. You feel good about the repair and have a real sense of accomplishment.

Now it is time to get the remaining tasks done and that means shutting off the Beomaster for a while and returning the display board to the bench for the segmented display repairs.

To remove the four LED segmented display modules you have to first desolder their connectors from the board in the back.

Then the plastic holder pieces are removed and the display modules taken out.

You can see more detail of the individual modules on the display reference post I made earlier.

I removed the plastic tabs that hold the display modules together and prepared the boards for new SMD LED replacements.

Here are the four boards after I stripped off the old LEDs. I also cut off the small tab trace I mentioned in the primer so the new SMD devices fit better.

This picture shows an original FM frequency display board next to one that is fully prepared for new LEDs.

Here are the FM frequency and source selection display boards fitted with new SMD LED devices.

This task is the most time consuming and tiring task on the Beomaster 8000 but quite rewarding when you put the restored boards in the test jig and fire the new LEDs up for the first time.

All sixty-five light up perfectly.

I will let these run for twenty-four hours before fully reassembling the modules for installation back onto the display board.

24 Hour Update...
I sealed the display modules up and double-checked that all segments still illuminate.

Beogram 8000: Trouble-Shooting Test Phase 1

I made the choice to try switching the Beogram 8000 control panel board first in the trouble-shooting of the intermittent record play interruption. This is the problem where occasionally the Beogram tonearm lifts to the Pause position while playing a record.

This is the easiest thing to check first and I kind of suspect the photo resistor circuit in the control panel on this Beogram anyway. When I made the service manual adjustments earlier in this restoration I noticed the adjustment for the adjustment screws were quite a bit different between the forward (<<) and reverse (>>). The adjustment screws control how much light shines on the photo resistor. The service manual says the normal voltage across those resistors (when forward and reverse are not engaged) is 620mV.

The following picture shows the control panel board removed. The position of the adjustment screws are where they needed to be to get the 620mV measurement. The difference in position of the two screws make me think one of the photo resistors is weaker than the other. Perhaps that is the reason for the fault I am trying to fix.

On the spare control panel board in the background you can see what I expect their positions to be like in relationship to each other.

One annoying thing about this adjustment is that B&O didn't provide good test points to check and adjust these controls without opening up the Beogram. It is easy to open just the control panel so if there were a nice test connector there I could check and make this adjustment after the Beogram is closed up.

The P5 connector pins 3, 4 and 6 are the nodes necessary to measure for this adjustment.
So I decided to add a test connector that I can access with just the control panel open. I also decided to do this test with one of my spare Beogram 8000 control panel boards.

I used a female connector for the end so I could leave the test connector attached. The picture above shows the test connector with the male test plug attached.

The test connector works great!  The Beogram 8000 is all closed up except for the control panel and I can easily use the test connector to make the adjustments.

I discovered that I will have to remove the test connector in this first attempt as the 24 gauge wires are too big and interfere with closing up the control panel all the way. If I want to have a "leave in" test connector I will have to go to a 30 gauge wire.

For now though it is time to return to the record play testing of this Beogram to see if the control panel was the problem. I am using the spare control panel board with the test connector and adjusted to the voltages specified by the service manual. On this spare board both adjustment screws are pretty symmetrical so that is a good sign that both photo-resistors are a pretty good match.

I am now on the last side of the second record play test. Only about eighteen more uninterrupted record plays (36 sides) to go for me to say the problem is fixed.

Beogram 8002: Taking the restored turntable for a spin

The last bit of repair on this Beogram 8002 is to fix the problems with the dust cover lid assembly. Meanwhile I started playing records on the Beogram as a test drive (or burn-in test). This is always the best part of the restoration.

I set up the Beogram 8002 in my office so I could listen to it play for the next couple of days. One of my kids is a trumpet player so I find myself listening to a lot of music by trumpet players. This picture is the Beogram playing Freddie Hubbard's First Light  LP. My copy has a very slight warp in it but the Beogram had no problems tracking it.

Once the listening tests are over and the dust cover assembly is re-attached this Beogram will be returning home.