Beogram 8000 dead

Hi Guys,

I've had an issue with my BG8000 turning itself off when it's supposed to drop the tonearm. The arm moves into the correct position, you hear the muting relay click and the unit turns itself off. After a few seconds it comes back to life and the tonearm returns to its resting position.

So I decided it needs a recap and a check of all those solder points....

Tonight I got it on the bench and reflowed the solder on all the edge of board connectors and the processor connector.

It's now dead... no standby light and no response to any of the buttons. The only sign of life is the light on the opto assembly is lit up.

Any ideas?

Lee

Hi Lee,

In times like this you have to get back to basics. Start with the power and work your way to operations.
Open up the Beogram into service position. Check the power from the transformer to the rectifier and verify the DC voltages. You have to make sure nothing funny is going on with the power or else the processor won't function. The transformer assembly has a fuse inside it so it is possible that is blown.

I also have to ask if you checked the solder joints you re-soldered under magnification. Those Beogram PCBs have a lot of small solder pads and it would be very easy to have a short between a couple without realizing it.

Double check your recap work.

It would also be good if you can post several detailed pictures of the boards (component and trace sides).

-sonavor

Reading your original post again, since your Beogram opto assembly light illuminates then the transformer fuse must not be blown. Still, check the power supplies especially the +5 VDC to the processor. It sounds like the processor is not functioning now. If you changed the small electrolytic 47uF capacitor inside the processor housing, did you make sure the ground was connected to that correctly? That capacitor is a little tricky to get installed correctly.

-sonavor

So feeling confident after fixing the Beomaster 8000 and having lots of free time due to furlough I thought I’d revisit this Beogram 8000.

I’ve checked all the connectors to the board and reflowed them. When testing for voltages I’m only getting 9v at c24 on the cpu board and around 1v at the cap in the processor can obviously way too low.

And pointers?

Cheers

Lee

Difficult now. It's always easier to find problems with natural causes than to start with something that was already "got at".
You may have introduced one or more new problems, that, combined with the original fault, could make diagnosing more difficult.
Having said that, you may - or may not - have cured the original problem. Difficult to say.
That's why I usually recommend diagnosing and repairs before doing upgrades, blanket replacings or "once overs".

But check your work.
Check if you accidentally connected two pins by flowing them together. 

Martin 

Hi Martin,

I’ve checked every single solder point that I’ve touched and can find no shorts. I’ve cleaned them all with isopropyl and looked under strong magnification. The only caps that I have changed are c27, the one on the regulator board and the two on the back of the main board.. The rest are all original.

Cheers

Lee

Did you make sure to solder the ground/negative side of C28 in the metal box with the microcomputer IC properly?  That board is a little different as it has some solder pads on the component side.

-sonavor

Hi Sonavor,

I haven’t replaced that cap yet. It’s still original and it looks ok from a soldering perspective.

Lee

Looks exploded to me...

And did you introduce the ground connection at C27, - the one that is lost when you take out C27?

Martin

I think that’s just a trick of the light Martin and the way the red wire is soldered on. The cap is definitely not exploded.

And sorry I meant it’s c24 that has been changed. Not the larger c27 with the 3 pins.

I think I’ve found an issue though...

When I worked on this 3yrs ago I connected the shielding for the black wire that runs from the cpu board to the little “bodge board instead of the centre white cable. I’ve now rectified this but could this have blown a transistor?

I am confused. In the photo you show capacitor C28. That is a 47uF, 10V electrolytic capacitor.  C24 and C27 are on the main board.

Anyway, I always change out C28 on a Beogram 8000/8002 restoration. It is key in the +5 VDC power for the microcomputer IC.
I change it when I am changing out the IC socket as it is much easier to get to when the microcomputer IC is out of the way.

If you just change C28 where it is you could just snip the existing leads and solder on to them. I don't like doing that unless I absolutely have to.
It is tight getting a soldering iron tip in there. 

The way the red and blue wires for the tiny board inside the microcomputer box are connected vary.
Here is a Beogram 8000 I restored that had them connected to +5 VDC and ground differently.

 

I’ve not changed c28 yet. Just the middle big cap on the main pcb (which is I believe c24?)

I’ve just had a go at changing c28 in the cpu can (it measured about 36uf) and I’ve managed to damage the negative pad on the top side

I agree - it's not exploded. But it's one I ALWAYS replace so I suggest doing that, though it won't most likely not be the reason for the current problem.

Martin

I’ve managed to change the cap in the cpu can but as expected it hasn’t changed anything.

Is the shielding on this cable supposed to connect to anything?

That wire is attached to the correct place.
Originally it was not soldered to the post on the board like yours is. The wire was attached to a single sleeve that fit onto the post.
Either way it is connected and the wire goes to the Microcomputer box.

I re-read this thread and have to ask if you checked the fuse that is inside the transformer box?

After that I would tackle the Beogram 8000 power supplies.
Check the DC voltages on C24, C27 and C29.  Then the +5 VDC capacitor C28 at the Microcomputer assembly.

-sonavor

The fuse in the transformer box tests fine.

These are the voltages I’m getting.

C24 - 9.29v

C27 - 19.94v

C29 - 21.62v

Cap in cpu box 1.05v

Hi Lee,

Those are a little low I think.
I usually get around 12 VDC for C24, 24 VDC for C27 and -24 VDC for C29.  C28 should have +5 VDC of course.

You are measuring about 3 volts lower on everything.
however, those should be enough for the regulators to produce +5 VDC, +15 VDC and -15 VDC so I don't think that is the problem.

I suggest pulling and testing 0TR1 as it sits between C27 and C28 to regulate the +5 VDC supply line.

-sonavor