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! 

Beogram 4000: A Fun Evening with a Smoking Solenoid Resistor

This is another installment of my 'A Fun Evening with...' series...;-). A Beogram 4000 that I restored this summer came back with a non-working arm lowering mechanism and the emission of a 'burnt smell'.

Oh well...I extracted it from the box and put it on the bench and removed the aluminum plates for a closer look.

After I plugged in and pressed ON, the unit started normally, but at the LP set-down point the arm would not lower. Instead the unit gave me a vivid demonstration of 'burnt smell', while a thin plume of smoke rapidly developed on the left side of the PCB that carries the carriage switches.

I quickly pulled the plug and lifted the PCB and found a browned solenoid resistor (7R1) and a blackened board:

I immediately thought the culprit might be the solenoid power transistor (0TR4) that regulates the current through the coil:

This TIP41 is usually a pretty resilient device, but in the case of the solenoid it also sees some pretty significant currents. I extracted it and put it into my transistor tester. And it tested seemingly o.k.:

This threw me a bit off the right track. First, I thought maybe the resistor itself had an issue (unlikely since it is wire wound, and it measured at 9 Ohm), then I suspected the solenoid (but it had its prescribed ~9.5 Ohm, i.e. seemed o.k.). 

I plugged the unit in for another measurement, and now the solenoid immediately activated after I plugged it in. Something had gotten worse. Since the solenoid is directly connected after the rectifier of the 24V rail this now really suggested that the transistor now was a permanent short circuit. 

So I replaced the transistor with a new TIP41C: 

Then I measured the original one again, and now it came up as a voltage divider, supporting my hypothesis:

Another good example to not blindly trust a transistor tester. They test at low currents and this can mean that results are displayed that have nothing to do with the actual situation the device is seeing in its circuit.

After bolting the TIP41C to the enclosure bottom, I plugged the unit in, and the solenoid did not activate anymore. Encouraged, I pressed ON and now everything worked as it should. The carriage went to the LP set-down point and the arm lowered. At that point I decided that I better also replace the solenoid resistor

and the two transistors that drive the TIP, 1TR10 and 1TR11:

I replaced the TR11 with a NTE128 and TR10 with a new BC547B:

The reason to replace these two was that in an earlier 4000 restoration TR10 was out of spec with a too low gain, and I increasingly think that transistors where the gain is critical or that carry a high current may need to be replaced during a full restoration of a Beogram 4000. Life is a learning curve! This is Beolove!