Beogram 4002 (Type 550x): New Main Capacitor Array with Integrated Efficient 22.8V Power Supply

Immediately after offering the new Beolover Efficient 24V Power Supply and Main Capacitors for Beogram 4000 component, I received inquiries about whether this part could also be used in AC platter motor Beogram 4002s (i.e. Types 550x).

The earlier AC-motor 4002s have a fairly similar setup when it comes to their main power supply. But there are minor differences: The rail voltage is only ~22.8V instead of 24V, and they do not splurge on a continuously powered standby mode like the Beogram 4000. But they also waste a similar amount of energy during operation due to the fact that the 45V transformer voltage is regulated down to the specified 22.8V with a Zener stabilized power transistor. This results in a nearly 50% energy loss in the 22.8V rail in the transistor.

In my design for the Beogram 4000 I replaced this setup with a modern buck converter-based design that has a DC-DC conversion efficiency in the 90-95% range. This causes the Beogram 4000 to run much cooler due to the reduced heat load. I provided a basic analysis and explanation of this setup in my original post about this design.

While the voltage difference is not really an issue, unfortunately, the different turn-on method in the 4002s without stand-by prevents the direct use of the Beogram 4000 board in the 4002s. Therefore, I designed a dedicated board for 4002s that also directly replaces the main capacitors and the voltage regulator setup. This is how the new board looks (it is available for purchase at the Beolover Store):

The many round capacitors are high-quality 105C rated Panasonic electrolytic capacitor arrays that provide the new power supply with appropriate reservoirs and couple the motor to the Wien oscillator amplifier. The row of small 'boxes' on the left is an array of Samsung X7R type ceramic capacitors that add up to the 150uF of the non-polar original electrolytic motor phase capacitor. Ceramic capacitors are much better for this application since they are inherently non-polar and they can take AC current much more easily than electrolytic capacitors. The circuit on the far end of the board is the buck converter based 22.8V power supply.

It replaces is this original setup:

The two larger capacitors on the right (0C1/2) are the in parallel connected reservoirs for feeding the voltage regulator whose transistor (0TR1) is bolted directly to the chassis right of the motor. The reason that this transistor is not on the main PCB is its significant heat dissipation that needs to be sinked efficiently. A significant part of the energy going into the Beogram is leaving it as heat at this front corner. That is the main reason that this area gets pretty hot after playing a couple records. Motor and transistor pretty much divide maybe 40% of the total heat load of the deck between them. The rest is mostly dissipated from the transformer, the solenoid (when the arm is down), the Zener that controls the regulating transistor, the incandescent light bulbs and the electronics.

The other two capacitor cans are to couple power into the motor (0C3) and to shift the motor phase by about 90% for the second winding (0C4).

This is a snippet from the circuit diagram showing the setup of the original power supply:

The buck converter that is integrated on the board basically replaces the 0TR1 transistor eliminating most of its power dissipation.

Replacing this setup with the new Beolover board is straight forward. Simply remove the capacitors and then unsolder all the wires from them and the transistor:

The transistor can/should be left in place.

Then solder the wires that were connected to the transistor to the respectively labeled pads at the bottom end of the board:

Then connect the four wires from the motor according to their color:

Here a shot from a bit further away:

Then solder the red and black wires from the rectifier:

A detail photo:

Next are the wires that go towards the PCBs: The green wire goes to the pad next to the motor wires, and the two orange and black wires to the pads on the right of the rectifier wires:

And that is it: This shows the board fully connected and bolted in:

And with the main board replaced:

Beolovely!

Like for the Beogram 4000 setup, I also measured the temperatures and currents before and after. This is what I got (33RPM, 13.2V motor voltage, arm up and carriage at rest):

Similar to the results for the Beogram 4000, a significant drop in temperatures occurred: The motor temperature dropped from 47C to 38.4C, while the temperature at the transformer went down from 38C to 34.8C. As a consequence the deck does not feel unusually warm anymore to the touch.