Beogram 4004 (5526): Replacing the Light Bulbs of the RPM Control Panel with LED Assemblies

A crucial step to make 400x Beograms 'fit for the future' is to replace their incandescent light bulbs with LEDs, which tend to last for a very long time. This helps preventing future breakdowns and trips to Beolover's bench. The RPM control panel of the Beogram 4004 contains two bulbs that provide the scale illumination. This shows the removed panel of the 4004 that I am currently restoring:

The first step is removing the bulb covers:

Then the bulbs can be unsoldered:

And replaced with the LED assemblies. This shows the assemblies pre-installation:

and after install:

They are designed to be 'drop-in', i.e. just connect like the original bulbs. The final steps are putting the covers back on

and trying them out:

The 'natural' incandescent-like glow is a result of using carefully tuned red/green LEDs on the assemblies. On to the DC motor!

Beogram 4004 (5526): Replacing the Light Bulbs in the RPM Trimmer Panel with LED Assemblies

The two remaining light bulbs to be replaced in the Beogram 4004 (5526) that I am restoring right now were in the RPM trimmer panel. It is a good idea to replace these bulbs with LED assemblies since they can influence the RPM stability of the platter motor due to their radiated heat that can change the resistance of the RPM trimmers in some cases.

This shows the RPM trimmer panel after taking it out:

I removed the bulb covers

and extracted the bulbs:

This shows the LED assemblies:

I installed them:

and put the covers back on:

This shows the 33 RPM scale illuminated by the LEDs:

The LED assembly combines red and green LEDs to achieve a 'natural incandescent' look, while providing red photons for properly illuminating the scale hand.

Beogram 4004 (5526): Replacement of Incandescent Bulbs in RPM Trimmer Panel with LEDs

Before the DC motor in a Beogram 4004 (5526) can be restored and tested it is a good idea to rebuild the DC motor control section of the main PCB and replace the incandescent bulbs in the RPM trimmer panel. The RPM stability of the platter drive system depends on all of these components. This shows the RPM trimmer panel as removed from the Beogram:

I removed the covers

and unsoldered the light bulbs:

Then I installed the LED replacement assemblies:

They are drop-in replacements for the light bulbs and include all necessary parts allowing running the LEDs from the 24V supply of the Beogram:

The covers fit like before:

This shows the 33 RPM LED in action:

The LEDs look very similar to an incandescent light bulb. This is the result of using red and green LEDs that are carefully tuned to resemble the emission spectrum of an incandescent light bulb.

Beogram 4002 (5513): Replacement of RPM Trimmer Panel Bulbs with LED Assemblies

After rebuilding the electronics of the Beogram 4002 (5513) that I am currently restoring it was time to replace the light bulbs in the RPM trimmer panel with LED assemblies. LEDs not only last much longer than incandescent bulbs, they also generate far less heat, which is beneficial for the RPM stability of the DC motor that drives the platter. This shows the RPM control panel removed:

To get to the light bulbs their covers need to be removed:

After unsoldering their leads they can be removed together with their aluminum clips:

The replacement LED assemblies

are drop-in and can directly be soldered into the same place:

These parts are available to other B&O enthusiasts. Just send an email or use the contact form on the right if you are interested in getting them.

Once this was done I replaced the covers and tested the panel:

The authentic 'incandescent look' of these LED implants is a result of using carefully intensity tuned red/green LEDs that can mimic the emission spectrum of a low emission light bulb. Now everything is in place to test the DC platter motor after its restoration, which will be next.

Beogram 4004 (5526): Replacement of Bulbs in RPM Trimmer Panel and Installation of New White Background Strips

After restoring the electronics of the Beogram 4004 (5526) that I am working on right now it was time to replace the light bulbs in the RPM adjustment panels with LEDs. This is not only good for the longterm stability of the unit, but it also helps alleviating potential RPM stability issues. The light bulbs heat up the trimmers in the panel and that can cause abrupt RPM changes while listening. LEDs run much cooler, and this eliminates this issue. This shows the panel removed from the Beogram:

The first step is to remove the bulb covers:

Then I unsoldered the bulbs and removed them:

Now it was time to solder in the replacement LED assemblies:

They are direct drop-in replacements that run on the same voltage as the bulbs. They are available to other enthusiasts, just send me an email or use the contact form on the right.

After replacing the covers

I fired the LEDs up for the first time. Unfortunately, this showed that I was not done yet, since it turned out that the white background strips behind the RPM indicators were wavy, which created a wavy illumination pattern:

This happens maybe in about 10% of the Beograms...not sure why some have it and others not. I had a look by opening up the RPM panel. This requires cutting the 4 locking washers that hold it down. One has to destroy them to get them to release the part:

You can see the wavy edges on both white strips. I removed them

and implemented cut to size replacements fashioned from white electrical tape:

Then I reassembled the panel. This required replacing the locking washers with new ones. I also use nylon washers that I put underneath:

After installing the RPM panel, the scales looked pristine again:

Beolovely! On to restoring the motor!

Beogram 4002 (5523): Replacement of the RPM Trimmer Light Bulbs with LEDs

After rebuilding the PCBs of the Beogram 4002 (5523) that I am restoring right now, it was time to replace the light bulbs that illuminate the RPM trimmers with LEDs. This is not only important to ensure long term stability of the Beogram, but also to improve the RPM consistency of the DC motor. The RPM trimmers are part of the DC motor feedback circuit that holds the RPM constant. Since incandescent bulbs emit heat the trimmers heat up during play, which can result in RPM changes. The much colder running replacement LEDs alleviate this issue.

This shows the extracted RPM panel from the back:

Removal of the covers reveals the bulbs:

After unsoldering the leads the bulbs can be pulled out and the LED boards inserted:

This shows the LED boards. They are drop-in replacements for the light bulbs:

These boards are available to other enthusiasts. Just send an email or use the contact form to the right.

The covers fit back onto the LED boards:

The LEDs illuminate the RPM trimmer indicators with a natural incandescent-like sheen while letting the indicator appear red. This is achieved by using red-green LEDs that are tuned to emit light similar to the spectrum emitted by a light bulb:

Beogram 4004 (5526): Installation of LED Light Sources into the RPM Trimmer Panel

After rebuilding the PCBs, the final step of the restoration of the electronics of a Beogram 4004 (5526) is replacing the incandescent light bulbs in the RPM trimmer panel with LEDs. This reduces the heat load on the RPM trimmers, which improves their stability over time. This is recommended since thermal changes can affect the RPM stability of the platter motor. Here is a photo of the panel taken out:

After removal of the two covers the bulbs can be accessed:

This shows the bulbs replaced with the LED based assemblies:

They are direct drop in replacements with the proper resistors installed to make the LEDs compatible to the 24V that are used to drive the bulbs:

The covers install exactly like before:

And this shows the 33 RPM LEDs in action:

They achieve a warm incandescent glow due to mixing red and green LED light in the right proportions to yield a color temperature similar to an incandescent bulb, while ensuring that red light is present to properly illuminate the red indicator.