Beogram 4004 Type 5526: Restoration work - Part 3

In today's post of the Beogram 4004 restoration work I completed the swapping of the Beogram 4004 RPM indicator lamps with the Beolover LED replacement lamp modules.

I also disassembled the Beogram 4004 keypad so I could clean the contacts.

First the RPM indicator lamps.
The following series of photos show the disassembly of the original RPM indicator lamps.

Now the photos of the installation of the Beolover LED replacement modules for the Beogram 400x RPM indicator lamps.

I have used every version of the Beolover RPM Indicator replacement modules and this version is the best and easiest to install.  Very nice.

Here are the photos of the Beogram 4004 keypad disassembly (to get to and clean the contacts).

The contacts don't look too bad in the photo but a closer shot of the contact points show the contacts to be quite tarnished.

After cleaning the contacts I coated them with some Deoxit and let them dry.

This Beogram 4004 is close to being ready for reassembly.

Beogram 4004 From Canada: Restoring the keypad

The keypad on this Beogram 4004 functions without any issues.  It is still a good idea to take a look at the contacts, clean them with Deoxit and a fiber brush. That will ensure that they continue working properly for many more years.

Another decision has to be made regarding the cosmetic restoration of the Beogram.
Most Beogram 4002 and 4004 turntables have some visible wear on the keypad button surfaces. Oil from human fingers wears away the original coating on the metal buttons over time.

This Beogram 4004 shows some of that type of wear.

The area of the panel where the buttons are is a polished steel plate that has been sprayed with a matte finish that gives it a brushed look. The contrast look of the design is a distinctive and classic look that makes the Beogram 4002 and 4004 turntables so great.

The owner of this Beogram wants that look returned as part of this restoration so I will exchange his keypad with one I had professionally recoated prior to lock downs.

I stripped off the remaining, original matte coating on the button plate then masked off everything else on the panel. I sent the keypad to a paint shop that could spray the button plate with an automotive grade, matte clear coat finish. It is a very tough finish that is used on automobiles so I expect it to last for a very long time in this application.

The keypad came back looking beautiful.

The two horizontal gaps between the button panel and the keypad frame was originally painted black. That needed touching up so I used some matte black paint for that.

Now on to the button contacts.

I began with taking off the Start button contacts first. 

After cleaning the two contact pieces with Deoxit and a fiber brush I reinstalled them and continued with the remaining buttons.

Contacts cleaned and treated, the button panel is ready to be reinstalled in the keypad frame.

The keypad is installed back in the Beogram 4004 and works like new.

I will replace the two lamps in the speed indicator displays next.

Canada Beomaster 8000: Filter & Tone Control Board

The next component for restoration on the Beomaster 8000 from Canada is the filter & tone control board. The audio signal of the selected audio source goes from the preamplifier board to the filter & tone control board where the bass, treble and filter circuitry lives. This board also has the Beomaster volume control which sets the volume level of the receiver output amplifiers according to control signals from the microcomputer board. The microcomputer board also mutes and restores the volume level when the selected source is changed. Another circuit on the filter & tone control board is for the FM signal strength meter.

Here is the board before the restoration work.

The trace side of the board has screws for securing the filter & tone control plastic panel. This board was missing one mounting screw so I will supply one when I reassemble the board.

Here is the board with the control panel removed. The restoration will involve reflowing the solder connections of the board connectors, replacing the electrolytic capacitors, replacing the LF353N opamps and cleaning the bass/treble slider controls.

Here is the board after cleaning, reflowing, recapping and new LF353N devices.

There is an adjustment procedure in the service manual regarding the left and right channel DC offset for the Beomaster 8000 volume control circuit. If the offset voltage is too high it will result in a static or clicking noise in the speakers when the volume is changing (up or down).  The two trimmers on the filter and tone control board are for adjusting out that offset. There are some associated fixed resistors next to the trimmers that can be disconnected as needed to aid in the offset trimming. The board above has two of those resistors (one in each channel) disconnected. Once the Beomaster restoration is complete I will go through the volume DC offset procedure and readjust the trimmers as necessary. I have found they usually do require some sort of adjusting.

Beogram 4004 Type 5526: Keypad Contact Cleaning

My Beogram 4004 project is about ready to wrap up. The dust cover has been polished and the keypad surface was refurbished at Beolover's workshop. After reassembling everything I found that some of the keypad buttons were not responding consistently. That usually means the contacts are dirty so I removed the keypad contact board to take a look.

Sure enough there was quite a bit of oxidation.

The contacts look pretty tarnished but it isn't anything a fiberglass brush can't fix followed by some Deoxit contact treatment.

This looks much better.

The Beogram 4004 controls are now working perfectly again.

Beomaster 8000 Keyboard Restoration/Not Working Buttons

The final step to restore my Beomaster 8000 to its original glory was to fix a keyboard issue. I noticed earlier that the TP2 button only worked intermittently. I thought that this was a problem originating from corroded keyboard contacts since wiggling the button seemed to do the trick once in a while.... Hence, I took the keyboard apart to clean the contacts. While this was an interesting exercise, it turned out that this did not fix the problem. But more about that below. First a few pictures of the keyboard innards:

Removing the retaining washers turned out to be a pain. Since B&O used one-time use washers that need to be destroyed for removal I had to cut them off with a wire cutter:

This photo shows the buttons from below after removing the PCB and a plastic foil:

Here a shot of the PCB before cleaning:

For cleaning the contact pads have to be removed:

These contacts were quite oxidized (or probably rather sulfidized, assuming that the pads are silver coated)

Using a small head Eurotool fiber brush (I am grateful to Gunther at Beoworld.org for this excellent tip!!) I cleaned the contacts:

The above picture shows the PCB after reassembly.

I reinstalled the board using 3 mm external retaining rings from Grainger (113828) and #4 nylon washers. This is shown here:

So far so good. Plugging the keyboard back into the Beomaster and turning it on immediately revealed that this procedure did not fix the problem.

After playing a bit around I realized that the P4 button also not worked whenever TP2 was out. A look at the circuit diagram for the processor board immediately revealed that TP2 and P4 use the same input on the slave processor (it distinguishes between the two buttons via the strobe mechanism that also drives the LEDs of the display in three "phases"). The oscilloscope showed that after pressing the TP2 or P4 buttons the voltage at P81-7 (7th pin on plug 81 that goes to the microcontroller) was higher than on other pins connected to working buttons. This led to the conclusion that the connection between switch and microcontroller must be interrupted whenever the buttons ceased operation.

Hooking up an Ohmmeter between pin 7 and R103 indeed revealed a broken PCB trace, with an intermittent contact depending on the flex of the PCB in the vicinity of P81. I installed a bypass (pink wire in picture):

This seems to have done the trick. TP2 and P4 seem now stable.

After this I finally put the Beomaster back together. Tomorrow, I will swap it with the one I currently use in the living room and the next months will show if this rebuild is stable. At this point all features seem to work correctly. On to the next B&O!