Reply To: Beolab Penta 2 running hot, can’t adjust bias

[Glitch]

The transistors and load resistors “look” similar to my working Penta2’s (i.e. no obvious overheating). I wouldn’t mess with them right now.

Probably not the problem, but are you sure you have the trim 100 and 220 trim pots in the correct location?

While you are double checking… check the polarity of the power supply capacitors. I recall that the markings on the original capacitors could be misinterpreted.

The soldering on some of the transistors doesn’t look like I would expect coming from the factory. I would clean-up the flux residue and do a closer inspection. It might be just the camera angle, but the solder from TR32 seems close to the trace.

I would carefully inspect the board connections even if you didn’t touch the connectors. I use either a 7X loupe and a bright light or take a picture with a macro lens and zoom in on the pictures on the computer screen. Even if I don’t find any obvious issues, I usually reflow solder on the board connectors as a precautionary measure.

I had trouble setting the bias on one of my other B&O amps. It turned out to be a bad ground connection to the preamp. The symptoms were similar to what you described where the full range of adjustment on the trim pot wouldn’t get the bias to a proper value.

I am also interested in hearing from others the possible causes for the amp running hot.

Glitch