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

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

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

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?).

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

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:

(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