Beomaster 4400 Type 2419: Personal Project : Main PCB Recap, New Reservoir Capacitors, New Trimmer Resistors

It may look low profile and small but recapping a Beomaster 4400 is quite a big desoldering and soldering task.

I finished replacing all of the electrolytic capacitors and trimmer resistors on the Beomaster 4400 main board. I also installed an arc suppression device like I installed on the previous Beomaster 4400 restoration project. The purpose of that device is to provide extra protection to the Beomaster power switch contacts.

Here is the Beomaster 4400 after the recapping (the before photos are in the previous post)

Here are some closer shots of the inside of the Beomaster 4400 after the recap.

and here is a closer look at the reservoir capacitors and the arc suppression device.

With the main board and chassis completed I can move on to the three FM boards and the preamplifier board.

Beomaster 2400 Type 2902: Recapping the main board and the volume control board

I completed the capacitor replacement on the Beomaster 2400 main board and volume control board. This included replacing the reservoir capacitors and the idle current adjustment trim pots for both channels.

The Beomaster 1900 and 2400 receivers are not my favorite units to replace capacitors on. They are very compact and low profile which make things a little cramped inside. Unlike the large Beomaster 8000 these smaller Bang & Olufsen receivers do not have easy accessible and removable circuit boards for working on.

Here is another picture for the Beomaster 2400 before the main board recapping.

You can see there are a lot of capacitors to change out. About eighty capacitors out of the ninety-nine total I will be replacing.  I can't easily disconnect the main board from the rest of the Beomaster 2400 to remove it for recapping as it has several hard-wired connections to the transformer and power supply.  On a Beomaster 1900 one time I removed everything from the cabinet chassis but that still made maneuvering the board awkward as I had the weight of the still connected transformer to deal with.

Since then I like to disconnect the FM tuner box, reservoir capacitors and heatsinks so I can switch from front and back of the main board while recapping.

I remove a couple of solid wires to the transformer to avoid breaking them while working on the main board.

After that it is a careful and tedious ordeal of desoldering and soldering while switching from the component side of the board to the trace side...back and forth.  This is another picture of the main board after the recapping work was completed.

There was one 10uF, 63VDC capacitor under the metal shield box for the remote control circuit.

I usually replace capacitors with values of 4.7uF and smaller with WIMA MKS capacitors.
An exception is if the WIMA won't fit well as with the two small 4.7uF capacitors on this small B&O adapter board.

This picture shows the two Beomaster 2400 idle current trim pots after I replaced the originals.

When installed back in the cabinet frame the emitter resistors are difficult to attach probes to for making the idle current (or no-load current) adjustment. While I have the main board in service position I like to make sure the leads on the emitter resistors are long enough on the trace side of the board to clip measurement probes to.

This picture shows the +15VDC supply reservoir capacitor after the recap. I used a little bit of Aleene's glue to secure it in place.

The two large 5000uF reservoir capacitors are kind of a pain to change out on these types of Beomaster units. The original capacitor terminals are soldered together as well as all of the connected wires.

In my replacement reservoir capacitor assembly I use small terminal connectors to attach the wires to the capacitors and the two capacitors to each other.

That is a more secure connection and makes future desoldering of the reservoir capacitors easier.

The small volume control board only has six small capacitors to replace.

That leaves one capacitor in the FM tuner box to replace and a few capacitors on the tone control and FM tuning control board. Then the recap work will be complete.

Beogram 4004 Type 5526: Recapping the boards

There are just two boards to replace capacitors on in the Beogram 4004. In addition to the capacitors there are two relays that can eventually fail so I always replace those with a modern sealed relay assembly supplied by Beolover. The relay on the main board is for platter speed selection (33⅓ RPM & 45 RPM).  The relay on the output board is for the phono cartridge muting. There are two trimmer resistors on the main board that I also replace. Those are the platter speed adjustment trimmers. The replacement trimmers are sealed, multi-turn type trimmer resistors.

Here is the before picture of the main board.

Here is the main board after the updates. The 1C10 capacitor was changed from its original 0.33uF value to 10uF. The reason for that is due to the rebuild testing of the DC platter motor. When Beolover rebuilds the motors he tests them for stability using the different 1C10 capacitor values that Bang & Olufsen used in these turntable controllers. On the tests for this rebuilt motor Beolover found the 10uF value to be the best pairing.

Now for the output board. Here is the before shot.

...and the after shot. Note that I added a small switch to the output connector to allow shorting signal  ground to system ground. That shouldn't be necessary when connecting the Beogram 4004 to a Bang & Olufsen amplifier via the DIN plug. However, when connecting to a non-B&O preamplifier there can sometimes be a hum in the signal. The Bang & Olufsen provided adapter cables for DIN to RCA plug type hookups included an external grounding wire for this purpose. The switch makes it convenient to just set the grounding as necessary inside without an extra wire.

There is one reservoir capacitor in the Beogram 4004 cabinet that needs replacing. I replace that capacitor with another Beolover custom part. The Beolover part is designed to mount perfectly in the original clamp.

Here is the new reservoir capacitor installed. It fits perfect and looks great.

Canada Beomaster 8000: Changing the reservoir capacitors and some rust (?)

After an unscheduled little break over the Labor Day holiday it is time to get cracking on these Beomaster 8000 restorations.

This weekend I started on the Beomaster 8000 from Canada, replacing the four 10,000uF reservoir capacitors. These are the reservoirs for the left and right channel ±55V rails.

Starting with the left channel

The solder posts on the replacement capacitors are just a small post and do not provide the nice mounting terminal the original reservoir capacitors had.

To compensate I add a small, flat terminal at each end of the connecting bus-bar.

After that I added mounting terminals to the five wires that connect to the left channel reservoir capacitors. I won't connect those yet because I will need the slack in the wires when I reinstall the left channel output amplifier assembly.

On to the right channel reservoir capacitors.

There is the same issue with the new capacitors and mounting the bus-bar.

Solved the same way.

I went ahead and connected up the five supply wires with their new terminals on the right channel. They won't be in the way for the right channel output amplifier installation later.

I was actually hoping to reinstall the left and right channel output amplifiers after their respective reservoir capacitors were replaced. However, when working on the left channel reservoir capacitors I noticed something odd on the cabinet base that looked like corrosion.

So I took a little detour on my restoration step order.  I went ahead and removed all of the Beomaster 8000 boards from the cabinet so I could fully inspect the inside of the cabinet base.

The corrosion was rather strange. It is only on the left side of the cabinet (when looking at the Beomaster from the front). The areas with the corrosion remove the cabinet black paint when I wipe it with a paper towel.

There is no corrosion on the right side. Just some dust that needs cleaning up.

Back to the left side of the Beomaster cabinet I wiped all of the nooks and crannies that had the rust.

On this type of problem I apply three coats of a rust neutralizer. It will turn the rust black. After twenty-four hours I will check the result and see if any rust has reformed. If it does then I will retreat the areas again. Once the treatment is satisfactory I will be able to paint the inside of the cabinet with black, rust protective paint.

This detour doesn't really hold up progress on this Beomaster project. I can proceed to work on the Beomaster 8000 boards I removed.  I will return to the cabinet in twenty-four hours though to see if it is satisfactory to paint.

Beomaster 4400 (2419): Reservoir Capacitor Replacement and Transistors Remounted

Last night I installed the two new 0C8 & 0C9 10KuF reservoir capacitors. These are the capacitors for the Beomaster ±35V rail voltages.

The replacement capacitors are a little smaller in diameter and length but I found some 105°C Nichicon capacitors that still fit into the Beomaster 4400 mounting bracket.

I reattached the ±35V rail voltage wires using some small terminals.

I added some heat shrink tubing for some added protection.

Here is the completed reinstallation of the reservoir capacitors.

Now I was able to resecure the main (PC5) board in the cabinet. I am using SilPads for the insulators and thermal exchange between the power transistors and the heat sinks.

This Beomaster is now ready for the reinstallation of the small boards.