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Beogram 8002 Repair

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sonavor
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sonavor posted on Sun, Dec 30 2012 12:21 AM

This Beogram 8002 was a recent find. I picked it up as a learning unit because one of my primary, everyday turntables is a Beogram 8002 I bought way back in 1983.  That original 8002 is still working well.  I had a B&O technician look at it about eight years ago and he made some adjustments.  That was before I took on this vintage audio hobby.  When this recent aquisition became available I decided the price was too good for me to pass up.

In the picture you can see the lid assembly is off.  The main spring and lid attachement came apart.  I am going to fix that first.

Electrically, this new 8002 powers on and the turntable starts spinning as soon as it is plugged in.  None of the pushbutton controls work.  So this could be a real troublesome repair.

 


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tournedos
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sonavor:
The electrolytic capacitor I hate replacing the most on these BG8002 units is the one inside the processor housing (C28, 47uF, 10V).  It is in a difficult place to remove and replace.  You have to be very careful.

Seems similar to the cap inside the processor board shieldwork in pizza box Beomasters. They are very dificult to remove because the circuit board with a heavy ground plane conducts all heat away from the soldering spots. I tend to just cut the old cap off, leaving enough stubs on the board to solder the new cap on them. Much easier and helps to avoid circut board damage.

--mika

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sonavor
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sonavor replied on Sun, Feb 17 2013 11:34 PM

chartz:

I don't want to be a pain in the neck, but I had a 8000 behaving like that and there were two problems. A bad solder at the motor connector and a tiny crack on one of the tracks leading there (I can't remember which one, I should have posted here! - hence the value of your work John).

 

Today I plugged the Beogram 8002 in (through my variac and dim bulb tester) and just left the turntable in standby mode for a while (about and hour).  It stayed in that state without any problems...the platter didn't start turning on its own like a couple of weeks ago.  Next I ran it through some commands: Turn, Play, Fast Forward, Reverse and Stop.  Everything seemed to work fine.  No flickering of the dim bulb tester at all.  I left the turntable in standby again for quite a while and observed no odd behavior.  Next, I used the Turn button to start the platter rotating and left it like that for about 20 minutes.  Again, no problems.

Finally, I started getting some minor flickering on the dim bulb tester when I tried to use the Play button again. It only briefly flickers but it does none the less.  So it appears there is still some problem in the drive circuit. Starting from a Stop (standby) position, pressing the Play button should result in the 8002 logic to look for a 33, 12 inch LP, then switch to 45 looking for a 7 inch single.  Part way into the search for a 12 inch, 33 RPM LP, the 8002 stops and returns to Stop. The problem appears to be with the turntable attempting to change speeds. At the beginning of the Play there is sometimes a flickering of the bulb as it starts out at 33 RPM, then again where the 7 inch record should be detected (and speed changed). I can override the auto-Play and use the fast forward button to move the tonearm to the full range of travel. When I am consistently seeing a flickering of the dim bulb tester lamp is on the speed change. So if I just start the turntable with the Turn command, I will see a flicker of the bulb when I push the 45 button. I also hear a slight (and very brief) electronic hum when the speed attempts to change. The coincides with the flicker of the dim bulb lamp. It is like the motor is groaning to change. Maybe it is a problem with the electronic braking?

I have a Beogram 8000 parts unit now.  There are some duplicate parts in that turntable that I should be able to swap out in my 8002.

Jacques, when you refer to the motor connector, are you talking about the PCB1 P4 connector?

-sonavor

 

sonavor
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For anyone that hasn't used a dim bulb tester, here is what mine looked like when I was testing with PCB1 P4 connected a week ago.  Note that my current problem with the bulb flickering during speed changes is much dimmer that what was the case when this picture was taken.


chartz
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chartz replied on Mon, Feb 18 2013 8:19 AM

P4 yes, that's the one. Now can you show a picture of your P4 please?

The groaning or humming at speed change seems normal to me. So the processor sends a reset signal at the speed change attempt? Does the speed detector do anything here?

Jacques

sonavor
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chartz:

P4 yes, that's the one. Now can you show a picture of your P4 please?

The groaning or humming at speed change seems normal to me. So the processor sends a reset signal at the speed change attempt? Does the speed detector do anything here?

 

Sure. Here is a picture of the PCB1 trace side and connectors - P3 and P4. 

After some additional testing I believe the problem is within the drive circuit path and relates directly with the motor drive attempting to increase speed.  When I start the platter turning using the Turn button I will often see a very faint flicker on the dim bulb tester.  By flicker I mean the bulb illuminates briefly then goes off.  As long as the platter keeps turning or returns to Stop, there are no more incidents with the tester bulb.  If I press the 45 button, I also see a faint flicker.  Pressing 33 again doesn't cause any problem. 

When starting from the Stop (standby) position and pressing Play, I also see a flicker on the dim bulb tester. That illumination is usually brighter.  After a few tests of that condition the problem appears to get worse where the flicker gets as bright as in the picture I posted previously of the bulb.  Pressing the fast foreward or reverse buttons don't affect the problem. 


chartz
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chartz replied on Mon, Feb 18 2013 7:28 PM

Can I see a bad solder joint at pin 3 or is it an optical illusion?

Jacques

sonavor
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Here is another picture of the OTR2 and OTR3 portion of the drive circuit that is on the Beogram 8002 chassis. The technical description document for that says OTR2 and OTR3 function as variable resistors in series with the transformer and stator.  I would like to swap out the small board that has OTR2 and OTR3 with the one from my Beogram 8000 parts unit. In my earlier trouble-shooting I found that disconnecting either the wire going to P4-3 or P4-4 will result in the dim bulb not illuminating.  I realize that removing either of those wires prevents the turntable from working at all but when I leave those wires in place and remove diodes D39 and D40 (preventing the down stream path of the P4-3 wire from reaching the brake), the dim bulb still illuminates.  So I think the best candidate to try next is to replace the OTR2 and OTR3 board.  I'm not sure if that is easy or not. I don't see an easy way to remove and replace that small board.


sonavor
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chartz:

Can I see a bad solder joint at pin 3 or is it an optical illusion?

P4-3 ?

chartz
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chartz replied on Mon, Feb 18 2013 7:36 PM

sonavor:

chartz:

Can I see a bad solder joint at pin 3 or is it an optical illusion?

 

P4-3 ?

Yes. What is it, between the two power  transistors? 

 

Jacques

sonavor
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chartz:

sonavor:

chartz:

Can I see a bad solder joint at pin 3 or is it an optical illusion?

 

P4-3 ?

Yes. What is it, between the two power  transistors? 

 

This picture shows P4-3.  It looks okay but I will check it again.


Menahem Yachad
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And adjacent to the tachodisc, the joint above the number 6 engraved on the PCB. Below the ITT 1N400x, there are 4 solder points in a row. Look at the 3rd joint, how the copper wire is soldered onto it.

sonavor
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Menahem Yachad:

And adjacent to the tachodisc, the joint above the number 6 engraved on the PCB. Below the ITT 1N400x, there are 4 solder points in a row. Look at the 3rd joint, how the copper wire is soldered onto it.

You are referring to this part of the picture.  The third solder pad has no wire connected to it.  The Stator 4C1 wires connect to the first, second and fourth pads.


Søren Mexico
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And this one

Collecting Vintage B&O is not a hobby, its a lifestyle.

sonavor
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On that picture the brown wire and the blue wire are where I disconnected the signals (P4-3 and P4-4) to help isolate the problem.  I have verified in re-soldering them that those connections are good. They just aren't pretty.  What I would like to do, if possible, is replace that whole small board (and components) with one from my spare BG8002. 

-sonavor

sonavor
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I suppose the easiest thing to try next is just to rework that OTR2 and OTR3 board - resolder everything and replace all of the components.

-sonavor

sonavor
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I figured out that all I had to do to remove the drive pcb was to slide it out of the plastic clips towards the center of the turntable.  With the small drive pcb removed I replaced it with the drive pcb out of my spare Beogram 8000.  The BG8000 is a non-working turntable that I got as part of a whole 8000 system (none of the 8000 system pieces are in working order).  I plan to use this Beogram 8002 in its place.

With the drive pcb replaced on the chassis, I repeated my operational tests.....same result.  So it would appear that the problem is with the drive circuit  back on PCB1. 


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