Beogram 4002 (5503): New Monolithic Beolover Carriage Position Sensor for AC-Motor Beogram 4002 (Types 550x)

A little more than a year ago I designed a replacement part for the carriage position sensor PCB in DC platter motor Beogram 4002 and 4004 (Types 551x and 552x). This board takes the guesswork out when the carriage position sensor does not work properly. The original design is fairly sensitive to the alignment between the IR diode and the photoresistor, as well as the alignment of the ruler relative ot the sensor, and it can be tedious to get everything properly adjusted.

The Beolover Carriage Position PCB for Beogram 4002 and 4004 (Types 551x/552x) is based on a modern monolithic IR photo-interrupter and circuitry that generates a clean and precise digital output signal for driving 1TR17 on the main PCB.

Sadly, this solution only works in the later DC motor Beograms. The earlier Beogram 4002 with AC platter motor has a much more complicated hard-wired carriage position sensor PCB that is not very easily replaced. But when I recently restored an AC motor Type 5503 Beogram 4002, and it gave me grief with detecting the runout groove reliably, I thought it would be nice to have a solution for these models, too!

Since replacing the entire board is complicated and unnecessary, I designed a replacement for just the sensor part of the board. I designed a board that simply piggybacks onto the main PCB, replacing only the original sensor bulb and photoresistor. This board adapts the same reliable circuit that I used on the DC motor PCB. 

This shows the final version of the Beolover Carriage Position Sensor for Beogram 4002 (Types 550x):

Let's see how it is installed:

This shows the original setup. The photoresistor is in the black housing in front of the 'plexiglass ruler' bolted to the carriage assembly:

After removing the two screws that hold the ruler assembly in place, it can be removed. This reveals the black bulb housing under the ruler.

Here is a view from a different angle (I already had the orange capacitor and white solenoid resistor replaced when I took this photo):

After removal of the bulb cover, the bulb is visible:

The first step for the installation of the new Beolover Carriage Position Sensor for Beogram 4002 (Types 550x) is removing both the photoresistor and the bulb and cleaning the five solder pads indicated below of all solder:

This is best done with a desolder gun since the pads need to be clean and flat so that the Beolover board can be placed onto the original board surface. The board needs to be aligned as shown in the picture below:

This shows it aligned and soldered in place:

When aligned properly, the three round connection vias on the Beolover board are aligned with the respective solder pads where the board connects to power and the base of 1TR17. All that needs to be done at this point is to put a bit of solder inside the vias.

It is a good idea to solder one via first and then adjust the board precisely, while making sure it is fully flat on the original board surface. If it is not flat or misaligned, it may be difficult or impossible to adjust the plastic ruler for proper function of the position sensor.

This shows the plexiglass ruler assembly bolted back into place. 

Adjust the ruler that runs at a constant ~1mm distance from the front-facing part of the sensor during the entire travel of the carriage.

Flipping the switch in front of the sensor activates the on-board LED:

The LED makes it easy to test the proper functioning of the sensor. It should light up whenever a black bar passes between the legs of the sensor.

After installation of the sensor, the Beogram reliably recognized the runout grooves of all records I played. Beautifully!

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...;-)

Beogram 4002 (5513): Installation of Upgrades - Universal Power Supply, SyncDrive and Internal RIAA Pre-Amplifier

I just sold a Beogram 4002 (Type 5513) to a customer in the UK. The restoration of this unit is discussed in this post. The new owner wanted to be able plugging it in in the UK without using a 110-to-220V transformer (Type 5513 Beogram 4002 have a supply preset for 110V). This issue can be addressed by installing a modern 'universal' power supply that can work with any grid voltage between 100V and 240V (read more in detail about this approach here). In addition to this new power supply he also wanted the Beolover SyncDrive and internal RIAA pre-amplifier installed.

I started the work by removing the hood and aluminum panels:

This unit had already received the Beolover Commander remote control before I put it up for sale.

First I focused on upgrading the power supply. This shows the original 'classic' transformer setup in place. The encapsulated transformer sits right next to the cable feedthrough and behind the fuse box. In other 4002 Types the voltage selector sits beneath the fuse box. In the 5513 type the voltage selector is replaced with a dummy plate and the transformer is directly wired for 110V only.

This shows the modern replacement, a Meanwell RS25-24 power supply which can operate on any grid voltage: 

It can supply 25W and has a tunable 24V±~4V output voltage range. 25W is more than enough since all the DC platter motor Beograms are rated 15W. This picture also shows the 3D printed adapter plate that I had to design for bolting it into its proper location, while using the original transformer mounting holes in the enclosure.

This shows the supply with bolted on adapter plate:

I removed the four screws that hold transformer and fuse box in place:

It seems best to cut the secondary wires of the transformer at about 40 mm. This results in long enough leads for connecting the new supply:

I soldered 3mm lugs to the cut off blue secondary wires and to new wires for connecting the new supply to the fuse box:

Then it was time to connect the new input wiring for the MEanwell supply to the fuse box. For this I unsoldered the wires going to the transformer (upper connections in the picture): 

and then I soldered in the new red/black wires. Here you can see them emerging from the fuse compartment:

Then I bolted the fuse box back into place:

The next step was bolting the new wiring to the screw terminals of the supply:

Note that the polarity of either connection is not important: The input wires are AC and the blue output wires connect to the rectifier on the main board that previously turned the secondary AC of the transformer into DC for the electronic circuitry.

At this point I also adjusted the output voltage of the supply to the maximum 28V that are possible with the RS25-24. This is done with the white trimmer on the right of the terminals as far clockwise as it goes. 

After adjusting the length of the input cable a bit at the cable gland in the enclosure feedthrough I was able to bolt the adapter plate to the enclosure bottom while smoothly routing the wiring through the 'channel' that I designed for this purpose into the adapter plate. This shows everything in place together with the sub-platter (there is a ~9 mm gap between supply and platter, enough for comfortable belt mounting:

Next came the installation of the Beolover SyncDrive. The SyncDrive is a synchronous motor driven by a dedicated digital control system. This gives it exceptional log-term RPM stability, similar to the later Beogram 8000/8002. This shows the original DC motor still in place:

The SyncDrive is a 'bolt-in and play' replacement for the original motor, i.e. there is no need for soldering. This shows it in place:

The red wiring harness connects to the RPM-panel jack on the main PCB. For this a small adapter breaks out the necessary connections to the red SyncDrive harness, while the original plug is also plugged into the adapter:

The final task was the installation of the internal Beolover RIAA pre-amplifier. The Beolover RIAA directly replaces the original output PCB of the Beogram, shown here still installed:

The Beolover RIAA is also a plug and play upgrade, i.e. all that needs to be done is unplugging the original board and then plugging in the RIAA board:

Then the keypad can be installed again.

This concluded my upgrade work on this Beogram 4002. I will now play it for a couple days to make sure there are no intermittent issues, and then it will be time to send it to its new owner in the UK!