Beogram 4000: Redesigned Drop-In Tracking Sensor Light Bulb Replacement

It was time to replace the tracking sensor light bulb in the Beogram 4000 that I am restoring right now with the SMD LED based replacement light source that recently I developed. I used this occasion for redesigning the part with the aim to incorporate the intensity adjustment trimmer into the light shield of the source to hold it firmly in place. I did not like that the trimmer was only held in place by the leads in my previous design, which resulted in a slightly wobbly appearance when adjusting it. In other words, this part was not yet fully up to Beolover standards!

So I designed a new circuit board which allows to directly solder the trimmer to it. This, however, required the concurrent redesign of the 3D printed housing part to enable the trimmer to protrude from the PCB. Here are some pictures. This shows the original light source.

This Beogram had the optional 100R trimmer installed that is mentioned in the supplement of the service manual. This allows the adjustment of the intensity of the light bulb which is a great feature that much simplifies the adjustment of the tracking feedback circuit sensitivity. 

This shows my redesigned part from the light source side. The LED is powered by 6V as it would in the Beogram 4000:

This shows the part from the other side prepared for insertion into the tracking sensor

The potentiometer protrudes through a opening in the plastic part and looks now fully integrated. Lovely! The negative lead is curled around one of the bolt holes. This makes the ground contact (the Beogram chassis is tied to the system ground). This setup essentially copies the original setup with the 100R potentiometer. The other lead is bent up to be able to go into the 6V rail solder point on the PCB from below:

After the installation I adjusted the tracking sensitivity to the prescribed 4 rounds of the record before the tracking mechanism kicks in after the needle is put into the groove. A few months ago I made a video about the tracking mechanism and the adjustment process:

Beogram 4000: Replacing the Keypad Light Bulbs with LEDs

The next step of my restoration of the Beogram 4000 that is on my bench right now was to replace the light bulbs in the control panel assembly with LEDs. I like to do this to increase the longevity of the unit and to guard against shipping issues. Incandescent light bulbs do not like vibration...Here is a picture of the opened up keypad:

The two bulbs at the top end are the bulbs that illuminate the unique position indicator feature of the Beogram. The vertically implemented bulbs below illuminate the RPM trimmers. I recently developed SMD LED based PCBs that replace the two position indicator bulbs (these parts are available - just send me an email). This shows the boards before installation:

The RPM trimmer bulbs can be replaced with standard red LEDs and current limiting resistors. Here is a picture of the implanted LEDs:

And after starting up the Beogram:

The position indicator LEDs are red-green LEDs tuned to appear with an incandescent sheen. This ensures that there are red photons to properly illuminate the red scale indicator.

This shows the LEDs at work after closing the panel back up. The red indicator is missing, since I did not reinstall the panel since I still need to restore proper functionality of the keypad switches. The unit has some issues with the slow scanning functions, which is an indication that the switches are corroded.

Very beautiful! What a nice design.

While I was in there I also glued the strobe light mirror back on (it often does off at this age):

On to the keypad switches!

 

Beogram 4000: Replacement of Incandescent Light Bulbs in Control Panel with LEDs

The Beogram 4000 that I am restoring right now had three broken incandescent light bulbs in the control panel. There are four bulbs, two for the position indicator and one each to illuminate the RPM trimmers. When I initially turned this deck on, no light came from any of the bulbs. Nonetheless, one of the position indicator bulbs was still o.k., but since the two bulbs that illuminate this indicator are in series, this did not help. At any rate, this is a perfect demonstration how fragile these bulbs are at this age, and that a replacement of them with LEDs is a great way to enhance longevity and reliability, and to make sure the unit survives shipping.

I recently developed dedicated SMD LED based replacement units that drop in for the position indicator bulbs. I assembled two and replaced the bulbs with them. I also replaced the RPM trimmer bulbs with high intensity red through hole LEDs fitted with appropriate 3.3k current limiting resistors. This brought them down to the proper intensity, making for a gentle but clearly visible low power illumination of the trimmer slots. 

Here are some pictures of the process. This picture shows the original light bulbs in place:

This picture shows the SMD LED PCBs that I used to replace the two position indictor bulbs:

and here after installing them and putting in the two red LEDs to replace the trimmer illumination bulbs:

After I was done with this I tested the functions of the keypad, and I had to realize that the deck does not switch to 45 RPM. Pressing the key did turn on the 45 RPM trimmer illumination, but the motor stayed at 33 RPM. This meant that the control system worked fine, but that there was an issue at the executive end of things. I traced the signal and found out that the relay that is responsible for changing the resonance frequency of the drive oscillator seems to have given up its ghost. It will be interesting to find a replacement.

Beogram 4000: Replacing the Light Bulbs in the Control Panel with LEDs

After replacing the reservoir and motor capacitors in the Beogram 4000 that I am fixing up right now, it was time to give the light bulbs in the control panel some attention. I always like to replace all incandescent light bulbs with LEDs to make these units more stable for the long run. There really is no reason to stick with light bulbs except in a few situations where for circuit or vintage looks reasons bulbs are still the preferred solution. In the control panel, LEDs can be used without penalty since there is no direct path of the light to the outside. In this particular unit, one of the bulbs in the position scale was out, which rendered the entire scale dark since the two bulbs that illuminate it are in series. 

I designed a small circuit board to hold two red/green SMD LED assemblies with their current limiting resistors designed to create a light mixture resembling incandescent light. I always use red/green LEDs if vintage scales with red indicators are to be illuminated. The reason is that amber LEDs that often can be used for incandescent bulb replacement do not emit red photons, and without them red items cannot be properly illuminated. 

The two light bulbs that back-illuminate the RPM trimmers were replaced with standard high brightness red LEDs and appropriate current limiting resistors. 

I made a brief video that shows the entire process from removing and opening up the control panel to inserting the LEDs and replacing the assembly back in the Beogram:

Here are a few pictures from the video:

These are the red/green LED assemblies for the scale illumination (Newark 75R0619 with 1.25k for red and 6k for green:)

The RPM trimmers were replaced with this (LEDs: Newark 08R2974 with 3.3k resistors - the photo shows 1k resistors, and that was way too bright):

This shows the LED assemblies installed:

And lit up:

This shows the control panel in operation with the LEDs in place. This looks pretty authentic. We decided to make the RPM trimmers a bit brighter than original to make them visible when the light is on in the room. The original brightness is so low, that one has to practically turn off the lights in the room to be able to see them at all. But this could of course be adjusted by using larger resistors for the LEDs. An identical look to the original very low brightness can also be achieved with low output LEDs (Newark 14N9416) and 220 Ohm resistors:

Beomaster 3000-2 Bulb Replacement

I recently repaired a Beomaster 3000-2, and the stereo indicator light bulb needed replacement. Unfortunately, these bulbs are difficult to come by. So I replaced it with a white SMD LED (LUMEX SML-LX1206UWW-TR 58K2313) that I mounted on a 1/8W 680Ohm current limiting resistor, which just fit perfectly into the plug that held the original light bulb. Bending the leads of the resistor created a reliable contact. Here are some pictures:

After soldering the LED across the 'bend' I cut the turn off, creating an in-series scenario for the resistor and the LED:

And fitted into the socket for the bulb. Proper fit needs a resistor that has the right diameter...you may need to try a few brands:

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Inserted into the Beomaster 3000-2 (I wrapped it onto a couple turns of Scotch tape to prevent accidental short circuits in the. Looks like a real light bulb!