Beogram 4002 (5503): Replacement of a Loudly Humming Transformer with a Modern Universal Power Supply

Oh well, after playing the lovely Beogram 4002 (Type 5503) that I recently restored I had to realize that the transformer made a pretty loud humming noise, which was quite noticeable during lower volume music passages. Especially, when placing the unit on a wooden sideboard the resonance of the wood amplified the hum to quite annoying levels.

I decided this definitely needed fixing before I could possibly sell this unit. A welcome project since I thought the initial crop of AC motor Beograms also needed a universal power supply upgrade similar to what I recently developed for the later DC motor models. 

Modern monolithic universal power supplies have several advantages over the original transformer/rectifier based setup: They are usually short circuit proof, they do not hum in any audible way and they mostly are designed to run on grid voltages ranging from 100V to 240V, i.e. can be plugged in anywhere on this planet. This feature also makes them brown-out resistant and they will also reliably protect the Beogram circuitry from voltage spikes etc...

The reason why my solution for the DC motor Beograms cannot be used in the AC motor models is these have a more than 3x higher power rating. DC motor Beograms are rated 15W, while the AC motor models are rated 50W. This difference is mainly caused by the AC platter motor, which is a power hog. This explains why the older Beograms get much warmer than the later ones.

It means that the 25W Meanwell supply I utilized for the DC motor Beograms is not powerful enough to run an AC motor model. Further investigation yielded that similar supplies rated for higher output had a too large footprint and would not fit into the space vacated by the transformer.

After a bit of poking around I found a more advanced design made by Traco that combined a small footprint with a 30W output: The TPP 30-D Series, which is a high-quality medical power supply. It is fully encapsulated and the output voltage can be adjusted (a rarity among this type of power block). The specific TPP 30-124-D (24V nominal) type can be adjusted to a maximum output of 26.4V by connecting an external resistor. This was great, but 30W is still not enough for the standard setup of an AC motor Beogram.

However, when combined with the Beolover Efficient 22.8V Power Supply and Main Capacitors for Beogram 4002 (Types 550x) 30W is enough. The Beolover 22.8V supply reduces the power consumption of the AC motor models significantly since it replaces the other power hog of this 1970s design, the linear voltage regulator, with a buck converter that has a high efficiency.

This shows the Transformer Replacement Kit for Beogram 4002 (Types 550x):

It includes the TPP30 supply mounted on the breakout board, the adapter necessary for bolting it to the enclosure bottom, the jumper for connecting it to the fuses assembly, the mounting bolts and a set of fresh fuses.

Let's see how I implanted the Traco TPP 30-124-D supply in this Beogram!

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Safety first: Potentially lethal voltages can be present during the installation of this part. Unplug your Beogram before installation. Ensure that the supply is bolted firmly to the adapter plate, and that the fuse box cover is in place before powering the unit up after installation.

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This shows the original setup:

The first step is unbolting the transformer and the (fake) voltage selector/fuse box housing. This shows the four bolts that need to be removed:

After removing them

the transformer and fuse box assemblies can be 'flipped' out of the enclosure:

The next step is disconnecting the transformer from the fuse box assembly and the rectifier. This shows the fuse box after removal of the fake voltage selector dial:

The grey wires come in from the power plug and the red/yellow wires go to the transformer primary windings:

I unsoldered the red and yellow wires and pulled them out of the fuse box assembly:

Be careful when you try this at home to not melt the plastic fuse box housing with the soldering iron. The next step was unsoldering the wiring from the rectifier (mounted beneath the floating chassis leaf spring next to the transformer):

This shows the unsoldered wires:

and the extracted transformer:

Now it was time to bolt the 3D printed adapter plate to the enclosure. It uses the same bolt holes that were used to hold the transformer in place:

This shows the adapter bolted in:

The next step is soldering the provided wire jumper to the fuse terminals previously connected to the red/yellow wires towards the transformer. This shows the wire jumper inserted from the bottom into the fuse housing:

And on the top side soldered to the fuse terminals. Left

and right:

It is a good idea to leave the fuses in place while doing the soldering. It will keep the fuse terminals in the proper orientation while they get hot.

Once the wires are soldered in, they need to be fed out of the fuse assembly through the 'exit channel' along with the grey power input cable:

Then the fake voltage selector can be stuck back onto the assembly,

which then can be bolted back to the enclosure:

This shows the fuse holder assembly back in place:

The next step is soldering the leads to the in- and outputs of the TPP30 supply's breakout board. First come the leads to the fuses housing assembly. They solder to the terminals "Input 100-240V AC~". Polarity does not matter since these wires carry AC:

Then the red and black wires originally connected to the rectifier output are soldered to the terminals labeled "Output 26.5V DC=". Make sure the red wire is soldered to the "+" labeled terminal and the black to the "-" labeled one:

Now the TPP30 assembly can be turned around and bolted to the adapter with the three provided screws:

Make sure that the in- and output wires are properly fitted into the cutouts on the adapter.

The final step is replacing the original fuses with the new 1.6A fuses provided with the TPP supply. It is easy to remove the original fuses by pushing them out with a suitable screwdriver:

 The new fuses provided with the kit can easily be pushed into the holders with a finger:

The final step is replacing the fuses cover. If it is not in place there will be potentially lethal voltages on the fuse terminals once the Beogram is plugged in. This shows the completed setup in place:

I plugged the Beogram in for a function test, and everything worked very nicely! Absolutely no noise from the supply! Beolovely!

Next I measured how much current the supply draws under the various operational modes of the Beogram.  As expected, the maximum current was drawn under 'play condition', i.e. platter motor running, solenoid engaged and the carriage moving towards the center of the platter. This shows the measurement:

The multimeter is connected between the fuse terminals on one side and set to its 10A range. In this setting it essentially acts as a small current sensing resistor in-between the fuse terminals, and the voltage drop across this resistor is converted into a proportional current reading.

The display shows 0.2 Amps RMS. This corresponds to about 24W power at 120V. In other words, the supply runs at about 80% of its maximum capacity of 30W. 80% is the usual engineering safe margin for reliable long term operation. All good in the power supply department! I should point out again that this new power supply only works in tandem with the Efficient 22.8V Power Supply and Main Capacitors for Beogram 4002 (Types 550x), which significantly reduces the power intake of the Beogram compared to the original setup. Therefore, please do not use the TPP30 supply if your Beogram runs from its original linear voltage regulator based 22.8V rail. It would not be safe and the fairly expensive TPP30 might suffer premature retirement...;-)

Four Beogram 4002 Keypad Restorations

I received 4 keypads recently from various customers. I'm going to restore them using the TangentialLab keypad restoration kit, which is available through the DKaudiolover store. Each keypad had typical signs of wear:

I didn't snap photos of the keypad plate removal process, but it's documented here. Once I had removed the original plate, the next step was to cleanup the frames. Here's what they look like after I scraped off all the glue using a #17 X-acto chisel, then touched up the black paint lines:

Next, I prepared all the replacement back pieces by applying the included adhesive promoter and VHB adhesive:

I completed the restorations by affixing the new keypad plates to the frames. The kit includes some handy alignment parts that make it easier to get it perfect every time:

I then applied the back pieces to each key and the center area:

Restored keypads are a really great finishing touch to any restoration, often returning the Beogram to near its original condition. I'll be returning these to their owners, where they should provide many years of great service.

Beogram 4002 (5513): Replacement of a Dead Transformer with a Modern Universal Power Supply

****Note added in proof: This solution will not work in earlier AC-motor Beograms (Types 550x). The Meanwell power supply used in this post is not powerful enough for those. There is now a dedicated solution available for the earlier Beograms. Please, see here.****

I am making good progress with the Beogram 4002 (Type 5513) from Louisiana. The unit had a short circuited transformer that needed replacement. During my initial inspection of the unit I found blown fuses and that some grey slime had leaked out from the transformer.

I decided to install a Meanwell RS-25-24 universal power supply like I did it recently with a couple of Beograms that I sent to the UK and Australia. Such modern supplies have a few advantages over the original transformers. They run on any input voltage between 100 and 240V and are short circuit protected. They also do not hum much, unlike some of the original transformers that often produce a noticeable 50/60 Hz hum when they are plugged in.

This shows the final result of my efforts:

The Beolover Transformer Replacement Kit for Beogram 4002 and 4004 (Types 551x/552x) is shown ere:

The Meanwell supply is shown flipped over with the adapter plate facing up. The plate allows the supply to be bolted to the same bolt holes that are used to hold the transformer in place. 

The wire harness connects the line-input of the supply to the fuses box. The additional solder lugs are used to connect the blue or blue/green wiring to the Beogram circuit to the Meanwell 24V output. The two screws are used to bolt the supply in place.

The provided 500mA fuses need to be installed in the fuses box of the Beogram. This ensures that the inrush current of the new supply does not overwhelm the fuses. The original 250mA fuses are not strong enough if the supply is plugged into 220/240 outlets.

Let's discuss the installation process:

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Safety first: Potentially lethal voltages can be present during the installation of this part. Unplug your Beogram before installation. Ensure that the terminal cover of the universal power supply and the fuse box cover are in place before powering the unit up after installation.

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This shows the primary wiring of the original transformer. Some cataclysmic event caused grey slime to emanate from the wiring orifice:

I removed the screws that fixed the transformer and the fuses box to the enclosure bottom. This released both components:

I first unsoldered the primary wires of the transformer from the fuse box terminals (be careful to not melt the black fuse box housing with the solder tip). Then I cut off the green and blue secondary wiring at the transformer housing. Next I installed 3 mm solder lugs on the secondary wires so they can be bolted to the output terminals of the new supply:

Make sure that the solder lugs connect to one green and one blue wire each. Both green and blue wires connect to rectifiers, i.e. their polarity is not important. Note that there are Beograms that have only the blue wires. In this case simply connect one lug to each of the blue wire ends.

The next step was soldering the grey wires to the fuse box terminals:

This is how it looks from the bottom side of the fuse box:

Both of the in and out wiring of the box need to be routed thought the 'exit channel' of the box:

Then the bottom cover of the fuse box can be stuck back on:

The next step is bolting the fuse box back to the enclosure:

Now it is time to connect the power supply terminals. The first step is removing the bolts from the two terminals on the left and the two on the right:

Then the wiring can be bolted to the terminals with the solder lugs:

The line-in wiring goes to the terminals labeled L and N.  and the gree/blue wires to the -V and +V labeled ones. The polarity of the wires is not important. Note that the ground connector in the center of the power supply does not need to be connected. The Beogram is a floating design based on galvanic separation via the power supply. 

Important: Make sure that the white trimmer potentiometer next to the terminals is turned all the way clockwise. This increases the output voltage to about 27-28V, which is beneficial for the operation of the arm lowering solenoid. In case you are worried about the performance of these modern supplies with regard to driving the solenoid, please, see here for some measurements that I did when I developed this upgrade.

Once the terminals are connected the new supply can be bolted in. The two small holes in the adapter plate fit to the original mounting holes of the transformer:

Just hold the new supply in place and put in the supplied screws from the bottom:

Then tighten them:

This shows the bolted in supply. Make sure the terminals cover is in place before plugging in the beogram!

This photo shows how the line input wire is routed from the cable gland at the enclosure orifice around the adapter plate to the fuses box. Also note how the green/blue wires go around the floating chassis and transport lock assembly towards the Beogram circuit board and Beolover reservoir capacitor assembly.

After the installation I made sure the terminals of the new supply were covered by the supplied plexiglass cover and that the cover was back in place on the fuses box. Then I plugged the Beogram in and pressed START. The carriage started moving and the arm dropped at the LP set down point! All good again in the power supply department of this Beogram!