Beogram 4000 Restoration Issue

[StanfordBeogram]

I have a Beogram 4000 (Typ. 5215) that I purchased for next to nothing at a local estate sale – my dream turntable! The power capacitors were leaking electrolytic fluid, so I did not even bother to attempt to power it on. I replaced the fuses and all the electrolytic capacitors on the main PCB with either Nichicon aluminium electrolytic capacitors or WIMA film capacitors. The power capacitors, Zener diode, and resistor were also all replaced with a power board I designed (like I did for the 4002/4 series).

The 4000 responds to the “ON” switch. However, the slide transport stops shortly thereafter with the motor still running and the strobe lamp on. I measured the DC voltage of C1 for 12V and C2 for 6V and could not get any voltage readings. I then measured the DC voltage of C3 and read 49.5V. For C4 I had a reading of 27.1V. In addition, none of the RPM indicator lights are lit – and I replaced the old Siemens relay with the new version.

It seems that one of the reed switches connected to C1 and C2 is bad or am I missing something else?

[hcraig244]

What do you measure on the input and output of the bridge rectifier 2D5 ? and have you checked the fuse hiding inside the yellow sleeve from the transformer to 2D5 ?

Craig

[StanfordBeogram]

Hi Craig,

Thank you for your post! I wasn’t even aware that there was another fuse in that section. Upon inspection, it is obvious something got very hot – either the fuse or another component, my (safe) guess being the fuse.

The yellow sleeve for the fuse is burnt and the associated PCB also looks burnt – after replacing the fuse, should I replace the other components near the dark area?

I will check the output of the bridge rectifier 2D5, once I get a new fuse and hear from you. Speaking of which – do you know what the voltage and amperage the fuse should be?

Ian

[hcraig244]

Firstly….is the existing fuse blown? no need to replace it if its good….I would buy a couple because often when you take these out the end cap becomes detatched and the fusewire pulls out of the glass holder, the fuse is 0.4A and sits in approx 14vac circuit.

The high temperature that has discoloured the yellow sleeve is heat generated from the voltage regulator circuit 2D4 (ZF6.8) 2R22 and 2TR6…..the fuse isn’t responsible for generating heat, this discolouration is very common as the regulator circuit does run hot…before you reconnect the fuse check you have the approx 14vac measured between the blue wire connected to the fuse and the blue wire connected to the PCB just above the rectifier…..this will confirm you transformer is giving the required voltage.

Craig

[chartz]

Where did you get that lovely Beo Hub board from?

I did have to replace a reed switch and a blown transistor on mine (TR6 I think?).

[Dillen]

One thing that kills transformers in these Beograms is rush-in current.
This is an issue particularly if the Beogram stood unused for a long time, and definitely if someone put in low-ESR filter capacitors.
The latter can be seen as an almost dead short right at the moment when voltage is applied, which puts a huge stress on the transfformer (and rectifier etc.).
Always bring a long stored Beogram up slowly on the variac for the first time to save the transformer.

Replacing one filter capacitor with two or more paralleled capacitors will only add to the risk of damaging the transformer as the resulting ESR (impedance) would be very low indeed.
The regulator would also be at risk, because of the reservoir capacitor it replenishes.
I wouldn’t recommend it.

Also, I am not sure what you measuring in the two photos with the multimeter.
Looks like the meter is in DC voltage mode while you measure on the fuses (?). And where is the reference (meter ground) connected?

Martin

[hcraig244]

chartz wrote:

Where did you get that lovely Beo Hub board from? I did have to replace a reed switch and a blown transistor on mine (TR6 I think?).

I have also had to replace the reed switch on a couple of these units, usually after i have invertedly grounded the 6vdc circuit…..its happened a couple of times when the carriage slide has moved too far in when i have been testing with the slider switches removed (schoolboy error)…..

[StanfordBeogram]

Hi Craig, Martin, and chartz.

Craig – the fuse did separate completely. I will order a couple of new ones along with a replacement of all the components (aside from the reed switches) of the voltage regulator circuit – might as well have the peace of mind for a few bucks and some time.

Martin – I was measuring the inputs on the fuses – in AC mode. The ground was chassis ground.

Question – if inrush current is problematic on these old Beogram transformers, could one simply install an appropriate thermistor to limit inrush current (and what would the ohms, amperage, etc would the thermistor need to be)? Or would a separate inrush limiter circuit need to be in place? I would love to solve this issue with the installation of a thermistor or new circuit. I found an example – see photo below.

chartz – The Beohub board is one that I designed for (a relatively easy) replacement of the filter power supply capacitors that simply installs in the old section with the chassis screws. I have created one for the 4000, 4002 AC, and 4002/4 models. I may make adjustments on the AC motor models (4000, 4002) given advice and guidance from Martin or others. Here are the boards:

[Dillen]

(Thermistor or current limiter…)
Modifying only to compensate afterwards would make little sense in my opinion.

Sorry to say it, but I would suggest replacing that lot of capacitors with single cans of good general purpose types.
I would fit can-types rather than PCB-mounts, exactly as B&O chose to do it. They have
a much nicer “oompfh” for this combination of motors, relays, solenoid and (at times sensitive to clean voltage) electronics.
This goes for the DC-motor versions as well.

And remember – no low-ESR capacitors in any power supply filtering positions in the classic B&Os.

Also make sure to find a bipolar cap with healthy ripple current specs.
Phasing a motor is hard work for a capacitor.

Mains has no reference inside the Beogram.
Chassis ground has no connection to any mains (it would potentially be lethal).
Mains go through the voltage selector and the fuses to the transformer.
Chassis ground is capacitively coupled to signal/electronics ground. If your deck has a three-prong mains plug, the chassis will be connected to the earth pin of the plug.
This means, that you can’t use chassis ground as reference for anything, really – not
for measuring around in the electronics either. Here you must use signal ground for reference.
For convenience I like to clip the meters negative pin to the common negative point of the large cans in the regulator circuit (after your modification no longer accessible in your Beogram).

Martin

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