Beogram 4002 (5513): Installation of a Modern Universal Voltage Power Supply

In recent months I received a few customer requests regarding fully restored Beogram 4002/4004 that I often have for sale. They wanted to know what it would take running US 110V models in Europe or Australia on 220V or 240V (unfortunately, most Beograms offered to me are 110V US models due to geographic constraints). My answer used to be: Get a small 50W 220V-to-110V transformer. Off course, the drawback with this approach is that there is an additional little box somewhere in the setup. Not very Beolovely!

So I set out to find a more elegant solution: The replacement of the internal transformer with a modern universal AC/DC power supply. These supplies are called 'universal' since they can take any grid voltage from 100V to 240V, i.e. they can be plugged in in any country around the globe. Another added benefit of such supplies is that they do not hum. The original transformers occasionally start making a 50/60Hz hum when the encasing resin gets old and shrinks a bit. When that happens the windings are not held firmly in place anymore and so they can start mechanically oscillating in the magnetic field generated by the 50/60Hz AC current. 

Voltage considerations: Modern off-the shelf supplies mostly put out 5, 12, 24, or 48V. The main power rail of the Beogram has a stabilized 21V. But the arm lowering solenoid is powered directly from the voltage coming out of the rectifier/main capacitor before the 21V regulator to give it a bit more voltage. This non-stabilized voltage is usually around 30V and depends on grid fluctuations since the transformer has a fixed conversion ratio, i.e. if the grid voltage goes down a bit, the voltage at the rectifier follows proportionally. This means they gave this setup a bit of 'headroom' so the Beogram would still work properly when everybody turns on their AC on a hot summer day. 

Another important factor for this project was that the footprint of the new supply would need to fit into the space of the transformer. 

With these constrains in mind I finally settled on the Meanwell RS25-24 supply as a promising candidate. Meanwell is an established supplier of power supplies. I have used them in the past for projects and also use them for my 3D printers. I think they have a high reliability.

Their RS25-24 supply is an enclosed type, i.e. is very safe to work with. It can supply 25W (the DC-motor Type 551x/552x Beograms are rated 15W, i.e. it has plenty of overhead for this task). The output voltage is 24V, but it is adjustable over a certain range, i.e. a higher voltage is possible. When I received it, this was the first thing I checked:

It turned out that the maximum voltage was 28V. This is a stabilized voltage, i.e. this will not change, regardless what comes out of the outlet in your wall. For a test, I connected the supply directly to the main reservoir capacitor of the Beogram (The Beogram was of course unplugged at this point!...;-) and pressed START. The Beogram happily came alive, found the LP setdown point and the solenoid solidly activated. It was hard to push back with my finger, very similar to using the original power supply. So it seemed the Meanwell supply was able to run the Beogram!

I started working on replacing the transformer. This shows transformer and fuse box still in place:

Fuse box and transformer are held down by two screws each:

I removed the screws and then I was able to lift both up:

The fuse box contains a dummy voltage selector that only serves as a vessel for routing the gray line cable to one side of the two fuses and the red/yellow wiring to the transformer after the fuses:

This shows the fuses-side of the assembly:

You can see how the wiring is soldered to the two fuse holders. I think they used two fuses since this design is a carry over from the real voltage selector used in earlier models, and for voltage selectors two fuses are needed to cover all the winding connection permutations properly (voltage selectors for transformers are a fascinating topic by itself, I could write a full blog post about it!...;-).

Mechanically the RS25 is pretty similar to the transformer

In fact, the mounting holes are identically spaced by 55 mm and both are holes for 3 mm bolts (albeit the Meanwell has threaded M3 holes, while the transformer uses self-tapping screws!). Maybe there is a standard for power supply mounting hole spacing depending on supply size! Unfortunately, this supply cannot be bolted in directly since it has a slightly different footprint that interferes with the power cable and the enclosure itself were the mounting holes used directly.

For this reason I designed a 3D printed adapter plate that allows placing the supply in the proper location while providing a 'channel' for the power cable to run under it and be out of the way:

The supply bolts on with two socket head M3x10 bolts:

I used a ~110mm long double stranded wire to make the connection from line-in to fuse box 

and cut the blue transformer output wiring at a suitable length so the other end of the wiring would fit perfectly to the output terminals of the supply:

I fitted two 3 mm solder lugs to the blue wires and secured them with some shrink tubing:

Here you can see the wires bolted to the supply terminals:

You may wonder at this point, why is the Beolover connecting wiring formerly conducting an AC voltage to the rectifier on the main PCB to the DC output of the new supply!? I could have of course done a clumsy soldered connection between the DC output of the supply and the output of the rectifier on the main PCB, since the rectifier is not necessary anymore for this setup. But why make something messy, if I can simply use the existing wiring harness which makes this a nice and clean install? A rectifier can naturally take DC, too. In fact it allows connecting the blue wires in either polarity to the supply since it will happily convert a negative voltage into a positive one, like it did it 50/60 times a second with the original AC input. The only slight drawback is that the current flows though two diodes in the rectifier, i.e. it will be lowered by about 2x 0.6V and the board only gets around 27V instead of 28V. But it seems 27V still works very solidly (see below), so this is not really a concern for this setup.

The next step was soldering the red/black line-in wiring to the fuse terminals. For this I stuck them through the holes that previously accommodated the red/yellow input wiring of the transformer

and then soldered the leads to the fuse terminals:

This shows everything placed for a preliminary fit:

I had to adjust the length of line-in wiring inside the enclosure since it now runs through that 'channel' in my adapter piece. This is easily done: Just pull out the cable gland by squeezing it with suitable pliers 

Here you see it pulled out:

And inserted back with the cable length adjusted:

Then I bolted everything in:

And tested whether the carriage would still have enough room to move completely beyond the end switch (ES) that turns it around when it sweeps an empty platter:

This experiment showed all good in the carriage movement department. I think I will move the Meanwell supply over to the left a couple mm more in my 'production' version of this setup. There is still a bit of room on the terminals side of the supply. Just in case...

An interesting item to look at after this conversion is the solenoid voltage behavior during engagement. This shows the voltage measured at the collector of 1IC4 (the pnp Darlington that drives the solenoid) with the original transformer setup:

This pretty much matches the schematic curve shown in the 5513 circuit diagram. When the solenoid activates the voltage starts out at ~30V and then caves to ~20V within ~20ms as the main capacitor depletes. Then the electronic limiting circuit kicks in and the voltage drops to ~2V for protecting the solenoid coil. 2V are apparently enough to keep the solenoid safely engaged against the return spring while the record is playing.

This shows the same measurement with the Meanwell supply installed:

The voltage starts out at about 26V and then also drops to 20V like in the original setup as current is drawn from the capacitor. In both cases the supplies are not able to fully provide the inrush current to the solenoid (~4 Amps), i.e. the main capacitor is essential for providing electrons for the brief moment while the solenoid engages. I think this is a very solid result for the RS-25 supply indicating that it is a good replacement for the original transformer setup.

In summary, I think this setup is ready for prime time and it can safely be implanted into single voltage DC motor Beograms to make them 'global players' (pun intended!...;-).

Note that this will not work for earlier AC motor models, since they require more power due to their wasteful (but great!...;-) synchronous AC platter motors. The AC motor Types (550x) are generally rated 50W, i.e. the RS25 series of supplies would not be powerful enough. Even though I am wondering if they might do the trick if the energy saving Beolover Efficient 22.8V Power Supply and Main Capacitors for Beogram 4002 (Types 550x) would be installed along with it.

Another interesting experiment for a lazy Sunday afternoon!...;-)