Beomaster 3000-2 (1970) made popping noise

Hi guys, I have a question, I was just listening to my Beomaster 3000 (slide rule model) when it made a popping noise on the left channel. It wasn't very loud, but it was definitely there. I immediately shut it down.

The receiver itself is in quite good condition. Recapped it a few months ago (except the tree big caps) and have been using it ever since.

How should I proceed on finding the defect? I don't want to kill my speakers while hoping it won't happen again.

If necessary, Parts won't be a problem as I have a spare one with a humming transformer but no other problems whatsoever (as far as I know).

Hi rjee, there are several things you could try. I recapped a couple of 3000-2s and found the DIN sockets can cause problems. The silver contacts tarnish and can become loose. It's possible to remove the pins by unsoldering and twisting straight to push back through the socket front. Cleaning (silver dip) and tightening solved the intermittent sound. You can check with headphones first to see if the DIN sockets are to blame. They are rivetted in place so not easy to swap the whole socket.

When you replaced the caps did you check the presets? These can disintegrate at the slightest touch and wiper goes open circuit. The 47k seem worst. Cuases all sorts of odd effects.

The three large capacitors (5000uf smoothing and 3000uF coupling) can also go low resistance when a voltage is applied. They may appear fine on a meter but breakdown above 35-45v. Most common blowing the main fuse at power up when the center one fails. When the output coupling caps fail it upsets the midpoint voltage. This could cause a popping it's on the edge of breaking down. You can check the caps by disconnecting and using voltmeter across the cap fed via a resistor (680R) to a dc supply - if the voltage does not make the supply the cap should be replaced. They should be rated up to 70v. Tell tale elecrolyte around the black rubber end cap / vent is another sign it should be replaced. I would buy new caps rather than swap from your spare as they are likely to suffer the same problems.

Good luck!

Rick