Beomaster 4400 Type 2419: Finding some power grounding problems

In the last post I ended with being successful in playing music through the Beomaster 4400 via an iPod Nano connected to Tape 1. The power on/off switch was not making good "on" contact and I had to help it connect by moving the "Off" switch very slightly.

I had intended on proceeding with some of the other audio source tests before revisiting the power switch but to my surprise the FM tuner was not functioning. Time to go over the Beomaster 4400 wiring again.

I soon discovered that I had a power grounding problem. The +15VDC regulator was no longer putting out +15VDC. It was at +22VDC and the regulator ground did not measure to the same power ground as the rest of the Beomaster 4400 power ground points. The Beomaster grounds should all be connected and also connected to the metal frame.  This Beomaster 4400 was not.

Carefully going through the boards again I discovered two broken traces on the PCB 5 circuit board. Both traces were for power ground and that explains the problem.

I'm not sure when exactly the traces failed but I believe it occurred when I was having the problem with the power on/off switch and when the fault relay was rapidly toggling. After that incident I did not notice the broken traces but I see them now.

These first two pictures are of a broken ground trace at the +15VDC regulator ground connection.

This second broken trace is at the ground connection between the FM3 PCB and the FM2 PCB.
The FM3 PCB gets its power ground from PCB5 via P9-2.  Power ground on the FM3 PCB routes to P5-5 back to PCB5 and over to the FM2 PCB connector P2-2.

The picture below shows the broken trace between those points.

That explains the problem with the FM source.  It doesn't expose the source of the problem though.
I repaired the broken traces but I will need to check out the FM1 and FM2 boards to see if they caused the problem or are the result of a problem somewhere else.

Too much current must have flowed through the broken traces. Perhaps they were already weak from an older problem. Interestingly during my testing of this Beomaster none of the fuses have blown during these power problems.

Here are photos of my repair of the broken traces.

The +15VDC regulator ground lead now measures as connected to the rest of the Beomaster 4400 power grounds again. I also measure continuity between FM2 PCB P2-2 and FM3 PCB P5-5.

As I mentioned earlier, I will have to wring out the FM1 and FM2 boards for any shorts to ground. I will check out FM3 as well just for good measure but it didn't have any signs of burned ground traces.

While I had the Beomaster 4400 front panel loose again I connected up my DMM to check the operation of the power on/off switch using the ohmmeter function. It confirmed what I had been observing when applying actual power on the Beomaster. The "Off" switch always disconnects the switch contacts but pressing a source switch (like Tape 1, Phono, Tape 2 or FM) does not. I can get the switch to make "On" contact by selecting Phono, then slightly press down on the Off button until I see the contacts engage on the ohmmeter. So there is definitely a mechanical issue there. That means removing the power on/off switch again and taking it apart.