Beomaster 8000: Rebuilding the Output Stages, Cracked PCB, Dead 5V Regulator Capacitor, and a First Spin

Before I start a Beomaster 8000 up the first time, I always rebuild the output stages with new 105C grade capacitors from name brand Japanese manufacturers and new quiescent 25-turn encapsulated current trimmers. This prevents the burnout of the output transistors due to corroded trimmers. And today this proved farsighted, since the right channel trimmer showed a resistance of 25k, which would have fried this output. I guess during shipping this trimmer went from problematic to dangerous.

Here are some pictures of the procedure:

Left channel PCB before rebuilding

And after:

This PCB also had a crack at the back. I bridged the one severed track with a wire to the next solder point:

 Right channel PCB before rebuilding:

And after:

Once the new parts were in, I disconnected all power and signal connectors from the PCBs and then ran them with external power supplies to check if their current intake is within specs...this way one sees immediately where the current goes, and which part of the output is damaged if there is an issue. This Beomaster still had o.k output transistors, and the measured currents were as usual 0.11A on the negative rail, 0.10A on the positive rail, and 0.01A on the control input after adjusting the quiet current trimmers. Perfect values. This means there is everything o.k. under the heat sink cover. Good news, since I do not enjoy replacing output transistors due to the heat sink goo that one needs to apply...;-).

Here is a picture of the right channel run from the external supplies. One can also see the multimeter showing almost 18mV across the emitter resistors, as it should be:

Now it was time to turn the Beomaster on, so I reconnected everything, plugged it in and the stand-by LED came on. Then I pressed a radio preset button - and nothing! Disappointing, but no show stopper: In such a case it is advised to measure the voltages on the u-processor board. And Immediately, the 5V rail showed only 4.2V, an indicator that there is an issue with the 5V supply. The 5V rail usually comes in at about 4.9V when everything is in spec. I immediately suspected 6C35, which is soldered directly onto the 5V regulator. Here are before and after pictures:

This one is often dead due to the higher temperature in this location. And indeed, after replacing the capacitor, which had a nice crack and showed only about 2nF when I measured it after the extraction, the Beomaster came on. And there it was - the way too bright frequency display:

This definitely needs fixing...I hope the PCB of this display was not damaged by our amateur friend.