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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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While I had the parts BG8000 turntable open, I decided to try the transformer from that unit in place of the one I have been using with my 8002.  The startup problem was worse with the BG8000 transformer. 

By worse I mean that with the transformer from the 8002 I can press Play (from the stopped/standby state) and have the tonearm travel all the way to where it reaches a seven inch record. At that point where it needs to switch to 45 RPM, the dim bulb tester flickers and the tonearm returns to the start position. Also, I can press the Turn button and the platter will turn. 

With the transformer from the BG8000, pressing Play or Turn will result in a larger flicker on the dim bulb tester and the platter will only try to start, then immediately stop.

Transformer to PCB1 connector pins P7-5, P7-11, P7-12 and P7-6 are directly involved with the drive circuit.  Of course other transformer pins provide the source for the positive and negative 15 VDC as well as +5 VDC.  The positive and negative 15 VDC are used on the IC3 preamplifier of the drive circuit.  The +5 VDC is used in the brake circuit. From earlier tests, I don't think the brake circuit is causing a problem.

I will recheck the wiring for the power to the drive circuit including the wiring from the transformer (P7) to the drive circuit. I will also start looking at the drive preamplifier section - IC3 (pins 1, 2, 3, 4, 8), TR27, TR28, TR29 and TR30 ...and related components.

sonavor
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sonavor replied on Tue, Feb 19 2013 10:17 PM

I tried a couple of easy tests this afternoon.  A quick thing to try on the driver circuit was to swap out IC3 on PCB1.  It is an LF353N (dual JFET Op Amp).  It was worth a try but didn't fix the problem (or even change the result).  Tonight I am planning on attaching some test leads to the drive circuit so I can monitor the signal on my oscilloscope. 

Another thing I tried today was to pop the metal top off the PCB2 box.  I wanted to see if more air flow would affect the nuisance display problem.  That result was the same as well.  Several minutes after power is applied (plugged in), the extra display segments light up. So I'll replace PCB2 IC2 (SN74247 7-Sement Decoder).

-sonavor

chartz
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chartz replied on Wed, Feb 20 2013 8:11 AM

Mmm... Still holding my breath here!

When you finally find the fault (s) we will be left with an extraordinary lesson John!

A lesson about patience and pugnacity too.

Jacques

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I'm waiting for the lessons everyday, the details, pics and explanations makes this thread even more interesting.

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

Rich
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Rich replied on Wed, Feb 20 2013 5:45 PM

Man, this is a great thread to follow.  Very inspiring.  Almost makes me want to get the 1970s BC5000 out of the attic and try again!

Almost.

I really ought to give that thing to John or Soren....


sonavor
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Rich:

Man, this is a great thread to follow.  Very inspiring.  Almost makes me want to get the 1970s BC5000 out of the attic and try again!

Almost.

I really ought to give that thing to John or Soren....

I have a Beocord 5000 that I bought back in 1977.  It is disassembled in a box waiting for me to get to it.  Unfortunately I have a bunch of projects to get to first. :)

-sonavor

sonavor
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I should add that the Beocord 5000 is a really nice cassette deck.

-sonavor

chartz
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chartz replied on Wed, Feb 20 2013 7:44 PM

sonavor:

I should add that the Beocord 5000 is a really nice cassette deck.

-sonavor

The reason why I've got two working!

 

Jacques

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Rich:
I really ought to give that thing to John or Soren....

I have a BC 5000 pizza box, and is very happy with it, but a BC 47XX will fit nicely to my, still in the workshop, BM 4400.

So, as John already have one, Rich, I'm open for suggestionsBig Smile, with backups like Jacques and John nothing can go wrong, Laughing

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

Rich
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Søren Mexico:

Rich:
I really ought to give that thing to John or Soren....

I have a BC 5000 pizza box, and is very happy with it, but a BC 47XX will fit nicely to my, still in the workshop, BM 4400.

So, as John already have one, Rich, I'm open for suggestionsBig Smile, with backups like Jacques and John nothing can go wrong, Laughing

If you want my Beocord 5000 Type 4716, it's yours.  Send me the McAllen address via PM.

 



Søren Mexico
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Rich:
If you want my Beocord 5000 Type 4716, it's yours.  Send me the McAllen address via PM.

Rich, you have a PM, thank you very much, an interesting project, I will do my very best.

When you have it, please let pay at least packing and shipping costs.

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

chartz
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chartz replied on Thu, Feb 21 2013 3:30 PM

A new thread is in the air!

Jacques

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chartz:

A new thread is in the air!

Oh yes, just got confirmation from Rich, but first I will have to finish the BM 4400, but the last week I was hit with a lot of work, and upon that Montezuma's vengeance.

 

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

sonavor
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sonavor:

Tonight I am planning on attaching some test leads to the drive circuit so I can monitor the signal on my oscilloscope. 

I connected my scope probe 1 to the drive signal between R104 (180 ohms) and P4-4.  I connected my scope probe 2 to R106 (330 ohms) on the side that goes to (c) - which is the transformer pin P7-11.  The pictures here are from the oscilloscope.  The first one is the Beogram 8002 at rest (standby).  The second one is with the platter turning .... after it is settled.


sonavor
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This picture shows what happens when the speed changes from 33 to 45.  I am not able to set up to catch the beginning of the transition from the steady turning to the acceleration but this picture is during the transition.  Notice that the AC voltage from the transformer pin P7-11 (c) dropped to zero volts.  That is when the dim bulb flickers.  The same thing happens when starting from standby mode to play.  Sometimes the speed transition is too severe of a load and the turntable immediately stops.  Sometimes it is just a faint flicker and can continue on to the play position.


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