Not necessarily. P83-1 supplies +5VDC from the Microcomputer board to a couple of other boards (Filter & Tone Control and Preamp).  P83-2 is ground so you would have just supplied ground so no problem there.

There is another 10/192 analog switch on the Filter & Tone Control board (PCB4) that is responsible for engaging or bypassing the filters (tone controls). Investigate the connections related to that. The control line for that switch goes from the Microprocessor board through the Display board and over to the Filter & Tone Control board where it arrives on connector P30-1.  So there is a connection between the Microcomputer and Display board to check at P75-1. Then the cable from the Display board P71-3 to the Filter & Tone Control board P30-1.

Connections and solder joints can be a real nightmare on the Beomaster 8000. 

-sonavor

So I’ve reflowed all the connectors on the CPU board. The filters are working fine again so small victory. But I’m still getting the issue with the sound becoming very quiet and distorted in PH, TP1 and Radio. TP2 never has any problems.

If I tap the unit lightly the sound goes back to normal so I’m thinking that could be a dry joint but could it also be a component?

And ideas on which connector or components could cause this issue? I’ve changed the switching IC on the preamp board so I don’t think it’s that.

Thanks again

Lee

Where on the board are you tapping?

To recap...
On yours we resolved that your BM8000 model has the B&O change between TP1 and TP2, right?
So TP2 gets switched in via the AD 10/192 analog switch. Is that the switch you swapped (with a spare you have)?
Both left and right channels are switched by one AD 10/192 analog switch.
The other sources get switched by two AD 10/278 analog switches (one switch per channel). The selection there gets routed to the single AD 10/192 switch (which has TP2).

From your decscription though I would tend to agree that it behaves like a connection issue. But it has to be at some point where the three affected sources have been combined. Maybe somewhere between AD 10/278 IC and the AD 10/192 IC. Anything before the AD 10/278 switch point would likely just affect one channel. Anything after AD 10/192 would also affect TP2.

-sonavor

Hi Sonavor and thanks again for your help.

Yes mine is the later version

And that is the chip I swapped.

It doesn’t seem to matter where I tap... I’ve really tried to narrow it down with the tap trick but the issue is so sensitive even a light tap fixes it for a few seconds.

Sometimes tapping on the CPU board fixes it and sometimes tapping on the preamp board fixes it.

I’m beginning to think it’s a faulty ribbon cable?

I’m going to fully disassemble the beast and have it all laid out on the bench to see if I can narrow it down further.

Thanks again

Lee

Hi Lee,

Have you ever changed out the Op-amps on the Beomaster 8000 preamplifier board?
If not you might try swapping 4IC5 with 4IC7...or better would be to change out 4IC5 with a new Op-amp.
4IC7 is for the source pre-out to the Tape 1 (Tape 2 in your case) record out ... so it isn't being used in the problem you are seeing.
I confess that I don't believe an Op-amp problem would be solved by tapping on the board but 4IC5 is in the signal path of the audio sources you are having issue with between the AD 10/278 switches and the AD 10/192.  
The only cable I can come up with that would relate to your symptoms would be the cable that goes from the Microcomputer board to the Preamplifier board 4P14 connector. That is the one that selects the audio source on the analog switches. However, it seems a little odd that a problem selecting the audio source would turn into the problem you are seeing. Still worth checking I think.

-sonavor

Hi Sonavor,

I changed all the OPAMPs a while back now so I don’t think it’s those.

I’ve invested in a new oscilloscope to do some testing to find out what the issues are. I’m just concerned about connecting the thing up as I don’t have an isolation transformer. Any advice on floating voltages and where I should attach the probes to ground etc.

Many thanks

Lee

Hi Lee,

I connect my scope probe using the 10X attenuation most of the time. I connect the scope probe ground to a ground point in the Beomaster 8000.
Just be careful to set up your probes with the Beomaster unplugged to avoid the risk of shorting something. Once your measurement probes are in place you can plug in the Beomaster and turn it on.

For your reference here is a youtube video that covers scope probes. The guy in the video is kind of a character but he covers the topic pretty well.

-sonavor

Just to follow up on this. Replacing the CPU sockets cured the issue. I’m still not sure how it caused the problem but hey ho. I think the preamp was being instructed to play the radio on top of the other inputs (apart from TP2).