Beogram 4000: Exchanging the Electrolytic Capacitors, the RPM Relay, and Adjusting the Motor Signal

I marched on with the restoration of the Beogram 4000 that is on my bench right now. After replacing the reservoir and motor capacitors, I went ahead and replaced all electrolytic caps on the main and power supply board with Japanese made 105C grade long lasting units. I also exchanged the RPM relay, since I recently extracted several dead or inconsistent relays of this type from Beogram 4000 and 4002 units. This made me think that these relays should be part of any 'full' restoration to ensure long-term stability. My goal is to get these elegant vintage beauties to a new-like performance and reliability. These pictures show the main PCB in its original state. This is the solder side. There is one Tantalum capacitor in the top left corner that was added post-PCB-design. Even the Danish masters go through a learning curve, I guess...;-):

Here is the component side:

And a detail shot of the RPM relay:

This is a picture of the relay component that I recently developed. It uses a modern encapsulated SMD relay that is broken out with a small PCB that fits precisely to the pinout of the original relay. Hence it can be plugged straight into the original solder pads and no external wiring is necessary. Plug'n Play!

This assembly is available to other enthusiasts. Just send me an email if you are interested.

This shows the PCB after replacing the capacitors and the relay:

This shows the replaced sole cap on the solder side:

On to the power supply board. It has only two Tantalum caps on it (the red dots):

And here with new ones:

After replacing the boards and testing that everything was working properly, I adjusted the motor signal. The AC motor is run by an on-board Wien bridge oscillator whose feedback needs to be adjusted for the right oscillation frequency for 33 and 45 RPM. There is also a potentiometer that controls the amplitude that goes into the power amplifier that finally drives the motor. I recently made  some more detailed posts (link 1, link 2) about the adjustment procedure. Here is a picture that shows how to apply the probes for the measurement:

One needs to be careful to select the right end of the phase capacitor to get the correct amplitude as prescribed in the manual for 33 RPM (6V). Here are the oscilloscope shots after I adjusted the trimmers to spec. This is the 33 RPM trace

and here is the one for 45 (it will usually be a bit lower than 6V and there is no way to independently adjust it - this is analog technology!..;-):

Beautifully clean traces in this unit! Absolutely lovely! This is Beolove!