Hello Martin,

Thank you for shipping me the cap kit quickly. Unfortunately same unstable spinning remains after the cap replacement.

As the tangential drive circuit is far from what I can comprehend (AC mixed with DC?), I've tried to isolate the problem by mixing and matching components from another well-functioning BG8002 and found that everything (things on the bottom plate like the tacho sensor, the 7805 regulator, TR2/TR3 etc., and the CPU box, the bipolar cap C1) is good except for the main PCB.

Any advice on what to do next with the main PCB? Many thanks in advance.

I'd appreciate any thoughts from other fellows here as well.

Michael

Did you replace ALL the caps in the kit ?
Is the wow related to the revolution of the platter, as in one burst for every revolution ?

Martin

Yes, all caps as illustrated on the diagram coming with the kit, including those on the bottom plate.

No, not one burst per revolution. It is continuous and dynamic abnormal pitch variation as the music goes.  Sort of apparent that the deck failed to maintain a stable spinning speed.

Looking at the block diagram of BG8000, in the Tangential Drive System area, I suspect the problem probably lies in the Integrator or Drive blocks, as the deck operates well in all keyboard functions except for pitch variation which may rule out the Brake and Settling circuits. But I've got no idea how to do further diagnosis... Please help and thanks.

Michael

Could be as simple as a broken PCB track or a cracked solder joint, that would not be the first time
for this type of board.
Let me get this right;
The two buttons (+ and -) has no effect and/or does not change the digits shown on the display ?

Martin

The + and - buttons work and change the digit display alright, and the pitch variation remains when we hit the buttons.

I've re-soldered all connector pins on the PCB as reminded by your diagram (some of them did show some crack). My impression when I did the cap replacing work is that generally the PCB track looks well . I'll certainly check that out one more time.

Many thanks.

Michael

Sometimes a microscope and/or strong light is needed to spot the fault.
The tracks on this type of board have a sad tendency to develop cracks
where a copper trace meets a solder pad, right at the edge of the solder cone, almost
impossible to spot.

Martin

Hi Martin,

Many thanks for the last reminding above.

With that in mind, I did my last try just before I give up to recover that PCB - to re-solder all those components on the PCB along the Tangential Drive circuit signal path. (Doing that I did find one resistor with one leg "loosely" covered by soder pad - not pushed into the PCB copper hole as it should have been.) And after the re-soldering, guess what, the BG8000 simply turns back to nomal spinning!

I've been trying to identify any failing component for weeks using multi-meter, and later, my scope - only to spot some good square wave generated by the tacho disc sensor. Without being able to catch up with those genius B&O engineer who designed the great stuff more than 2 decades ago, I learned that in fixing such excellent machine one could and need only try to recover basic things like solder crack or aged caps. The design had been so excellent that components on the PCB will be working in very good condition that they will not easily crash or burn themselves like we usually see in average electronic products!

So my salute to Beogram one more time, and also to Martin who's really a treasure here!

Michael

Hi,

Bad solder joints eh... rings a bell or two!! 

All, and I do mean all, Beo gear that have passed into my hands so far had this problem...

I too suspected bad components. Sometimes they are good, sometimes not so good, but the joints are often bad. On my two Beogram CD players, the passive components were still okay, but I realised that changing them (a good thing anyway) also revealed their solder joints were bad in fact, not the caps or resistors themselves!

This is not a B&O problem only of course!

And yes, Martin is our indispensable and always available teacher! 

Jacques