Beomaster 1900 (Type 2903): New Arrival

After a long series of Beogram projects I have a change of pace with a nice Beomaster 1900 receiver sent to us for restoration.

The AC plug is missing so no turning the unit on for any type of checks. I will give the unit a quick survey to see if anything major jumps out at me.

Turning it over I can see that it is missing its rubber feet.

Over all it looks great so far. Time to take a peek inside.

Nothing major but I do see that the bass, treble and balance indicator masks have some wear on them.
The bass and balance have bad enough wear to the point that the masks really need replacing. I will try to find replacements or print some of my own. The treble mask is in good enough shape that it could be used as a template to copy from.

Here are the Beomaster indicator lamps. I will get the receiver working again before looking at replacement options for the lamps. LED replacement is an option but some of the lamps are integral to their circuit operation so any replacement there will require more than just an LED and a load resistor.

Next step is to check my 105°C electrolytic capacitor stock to see what I have and what I need to order in recapping this Beomaster.

Beogram 4004 (5526): Restoration of the PCBs and a New Reservoir Capacitor

After rebuilding the arm lowering and tracking systems of the Beogram 4004 (5526) that I am restoring right now it was time to rebuild the electronics. I started with the main PCB:

This shows it in the original condition:

I replaced all the electrolytic capacitors, the RPM relay and the RPM trimmers:

This shows the RPM section in detail before

and after:

The RPM relay was replaced by a SMD relay on a breakout board that I developed a while ago:

The replacement relay board has exactly the same footprint as the original National relay. This part is available to other B&O enthusiasts. Just send an email or use the contact form on the right.

The original RPM trimmers were replaced with modern encapsulated 25 turn trimmers. Since they need to be adjustable from the solder side of the board, they need to have their solder terminals extended that I could install them upside down:

On to the output PCB. The 4004 has a remote control function when connected to a Beomaster 2400. This is the purpose of the additional circuitry on the output board (when compared to a 4002). This shows the board in original condition:

Upon closer inspection I found a burned out tantalum capacitor:

When I removed it it completely broke into small ash pieces:

An impressive demonstration why it is a great idea to replace all electrolytic capacitors at this point in time. I replaced all electrolytic capacitors and installed a new output relay:

This shows the output circuit in detail after the restoration:

The red switch in front of the output board header allows making a connection between signal and system grounds. This is a convenient feature to prevent humming if the Beogram is connected via an RCA adapter that does not have a broken out ground lead.

The final step was to replace the original reservoir capacitor:

They are also frequently out of spec at this point in time. The modern replacement is a bit smaller, and I used a 3D printed adapter to fit it into the same space like the old can:

All good in the capacitor department now! On to replacing the light bulbs in the RPM trimmer panel with LEDs.

Beogram 4002 (5523): Polishing of the In- and Outside of the Hood

After installing the Beolover 4002 Commander MkII remote control and the internal RIAA pre-amplifier board into the Beogram 4002 (5523), the final step was to polish the hood. As usual this hood had the typical scratches on the outside. Unfortunately, and unusually, this one also had a big scratch on the inside:

The inside is much harder to polish since one hits the corners with the polishing block, and it is impossible to polish all the way into corners and to the side panels. Fortunately, the scratch was a bit away from the edges and so I was able to work on it. The key to polishing an inside scratch is to enlarge the polishing area with each step to ensure that the scratches introduced by a polishing step are erased in the next at the fringes of the polished area. This shows the initial planarization step with 320 grit:

After my sequence of 10 polishing steps the hood was shiny again on the inside:

After taking care of the inside, I did the outside. This shows it in the condition as received:

And here the final result after polishing it back to translucency:

The final step was to install new rubber bumpers on this hood. They give it that happy 'thunk' sound when closing it against the wood plinth. Without bumpers the sound is much less dignified...;-). This shows one of the missing bumpers:

I drilled them out with a 2 mm bit: 

Then I installed O-ring snippets with some super glue

and cut them to size using a razor blade and a 3D printed template (~ 1mm keeps the hood horizontal when closed):

This shows the end result:

Beolovely! I will play this unit for a bit longer (I always enjoy restorations that include installation of my RIAA amplifier since it allows me to connect the Beogram to the Phono4 input of my Beomaster 6000!) and then it will be time to ship it back to its owner!

Beogram 4002 (5523): Installation of 4002 Commander MkII Remote Control and Internal RIAA Preamp

I recently finished up the restoration of a Beogram 4002 (5523). My customer decided to add both the Beolover 4002 Commander MkII remote control receiver (it works together with a matched Apple remote) and the internal RIAA pre-amplifier. I developed these two upgrades a while ago. More information about their performance and installation is given on the 4002 Commander page on the blog and in this post about the development of the RIAA amp.  Both boards are available to other enthusiasts. Just send an email or use the contact form on the right. 

This shows the two boards together:

The board at the bottom of the picture is the Commander MkII remote receiver board. The MkII version comes with a repeat function, which uses the CD4 indicator on the keypad cluster as indictor. It is a plug-and-play installation. The board installs into the keyboard header on the main PCB and is bolted into place using one of the screws that holds the PCB down. 

The RIAA amplifier is soldered directly into the output relay solder points. This shows the output board as I rebuilt it with a new relay and grounding switch:

For the installation of the RIAA amp I needed to remove the relay and the switch again to make space for the board and the connectors. This shows the output PCB prepared for the installation together with the RIAA board upside down:

The red 3D printed component serves as spacer to elevate the board above the black in- and output board headers. This shows the board after installation:

The original headers are still accessible, i.e. the Beogram can easily be configured in its original way by plugging the cables into the original headers instead of the white amplifier connectors.

This shows both installed in the Beogram:

Beogram 4004 (5526): Restoration of Arm Lowering and Tracking Systems

As usual, my first step of the restoration of the Beogram 4004 (5526) that recently arrived was to rebuild the arm lowering and tracking systems. This shows the arm lowering mechanism of the unit:

I removed the linkages and the damper for cleaning and lubricating:

This shows the parts spread out:

After reassembly it was time to get to the linkage that connects the damper with the tonearm. This shows the back of the arms:

Removal of the two screws at the bottom of the sensor arm enabled its removal:

I removed the retaining washer and the small spring underneath (careful here - this tiny spring likes to vanish very spontaneously) and removed the linkage:

After lubricating the pivot shaft I put everything back together and adjusted the arms to a parallel alignment:

This concluded the restoration of the arm lowering system. I moved on to the tracking sensor and the pulley that drives the carriage spindle:

I like to replace both since the light bulbs in the tracking sensor often break and most of the pulleys seem to crack at some point, which makes them wobbly and this causes unbeolovely vibrations when the carriage is driven. I removed the tracking sensor light bulb assembly. This shows the Beolover LED replacement assembly in comparison with the original unit. The LED is in the same spot where the bulb filament is located.

Like all Beolover parts featured on this blog, this part is available to other enthusiasts. Just send an email or use the contact form on the right. This is how it looks after installation:

Next was replacing the plastic pulley with one of Nicks awesome precision machined aluminum units:

I'd be happy to put you in touch with Nick if you want to get such a pulley for your own Beogram! I also put in a new belt, and that concluded the restoration of the tracking system. On to the electronics!