Bay Area Beogram 8002: Service Manual Adjustments and Record Play Test

On the remaining service manual adjustments I need the platter motor connector disconnected for a couple of them...The tracking force adjustment and the tracking sensor adjustment.

For the tracking force adjustment an MMC phono cartridge must be installed on the tonearm.
I also like to set the sliding tracking force knob to 1 gram.

The tonearm can then be moved over the platter (that isn't turning because the platter motor connector is disconnected).  With a tracking force scale on the platter I can measure the tracking force of the cartridge when it is lowered onto a record. In this case I should measure 1 gram on the scale.
In cases where a selected 1 gram on the tracking force slider doesn't result in a 1 gram measurement on the scale, the tonearm counterweight must be adjusted.

The Beogram 8002 tonearm counterweight mounts on the back of the tonearm assembly and is secured with a single screw.  To make an adjustment the tonearm counterweight screw is loosened and slid forward or backwards depending on whether increasing or decreasing the tracking force.

It often takes a couple of iterations to make the adjustment but it should end up measuring 1 gram on the scale.

The counterweight is secured and the next adjustment with the platter motor still disconnected is the record tracking sensor.

When the Beogram 8002 is in Play mode and the tangential arm assembly is moved towards the record platter you should see a glow from the tracking sensor lamp as shown in the picture below.

For the adjustment of the tracking sensor there is a small adjustment screw to the side of the sensor housing.

The adjustment procedure for this sensor is to place the tonearm (with a phono cartridge) onto a record.  There was originally a Bang & Olufsen test record 3621001.  Track 5 is what the service manual says to use.  I do have a couple of Bang & Olufsen test records 3621003 but I don't know if they are similar.
So my technique is to use a couple of vintage records I own to test out the record tracking sensor.

The actual adjustment is to manually rotate the platter (with a record) by hand and observe that the Beogram servo motor begins to advance the spindle within 2 ± 1 revolutions.  After that the spindle should advance on every revolution.

Here is a photo of the tonearm lowered onto my test record for the adjustment.

My final adjustment is for the forward and reverse scanning LDR devices.
They function fine but I need to see where they measure in relation to what the service manual recommends.

The service manual calls for 620mVDC on each LDR (after the Beogram has been playing for about 5 minutes).  I like to set the value at around 650mVDC.

The two LDR devices in this Beogram 8002 were just over 700mVDC.  That value still works but I adjusted the two adjustment screws to get 650mVDC on each LDR.

Once those adjustments were completed I ran through a number of Beogram 8002 functional tests.
Everything worked perfectly including the Pause function where the tonearm returns to the stop location and pressing Play returns the tonearm to the spot where Pause was pressed.  

Normally I would continue on and start reinstalling the turntable components back in the Beogram 8002 cabinet to start some listening tests.

However, I am not entirely happy with those scanning LDR devices.  I was able to adjust them to the values I wanted but the two LDR devices are quite different from each other in their settings.

You can see in this photo what one LDR adjustment screw is way higher than the other.

The two LDR devices are not expected to be identical to each other but they should be closer to each other than this.  The higher adjustment screw feels like it is at its limit.

Opening up the scanning LDR and lamp compartment I discovered that I was correct. One of the LDR adjustment screws was at its limit.  It could not be adjusted any more.

I don't like this type of situation.  While the LDR is in a good working position there is no room for any future adjustments as the sensor lamp starts to lose intensity.

Looking inside at the LDR devices and the lamp I can see that the lamp does appear to function okay.
 

The way the scanning sensors work is the lamp illuminates each LDR through two separate, metal apertures that move with the scanning pushbutton action.  Pressing a scan button on the Beogram 8002 control panel closes the aperture on the respective LDR.  That changes the resistance of the LDR and calls for more voltage on that direction of the servo motor (that drives the tangential arm assembly).

When neither of the scanning buttons are pressed the LDR devices are in their neutral state which should be in that 620mVDC to 700mVDC range.  The two large, black screws adjust how much light from the lamp strikes the LDR in that neutral state.

As a test I opened up the other LDR adjustment screw so that both LDR devices will get the maximum amount of light from the lamp.

I put the LDR and lamp assembly cover back on and applied a +15 VDC test voltage to the lamp.
With both scanning buttons in their neutral position I measured the resistance on each LDR.
One measured around 16kΩ and the other around 43kΩ.  Quite a difference!

As I said, the two LDR devices are not expected to measure identically but in this case one is way different from the other.  The LDR measuring 43kΩ in the test is the one that had to be adjusted to its travel limit during the adjustment procedure.

My next step then is to look through my parts bin for some spare LDR devices that I know I have.
I will have to test a few to find a good pair that are closer to each other.

I think I will also replace the sensor lamp.  I don't believe it is a problem yet but if I replace one or both LDR devices then I think I should also install a new lamp.

Beogram From North Carolina: Speed Control and Braking Working Again

The speed control and braking problem described in the previous post about this Beogram 8002 is fixed now.  It turned out to be an easy repair that was made easier to diagnose since I have the luxury of owning quite a few spare, fully functional boards for the Beogram 8002.  It is one of my favorite Beogram turntables and I have several that I use for my own use. 

So instead of diving into a search for a bad sensor, my first trouble-shooting step was to swap the Beogram 8002 control boards.  This would quickly tell me if the problem was a sensor or a board problem.

It was a board problem.  The swapped board worked perfectly. 
That meant the problem was either a bad connection or a failed component on the circuit board.
Before pulling parts it is always a good idea to carefully inspect the boards first.
Sure enough...I found a wire that came loose.  Looking up the wire's function made sense why it was causing the problem I experienced.  The wire was for the Beogram platter speed control.  It doesn't get more obvious than that.

This picture shows the speed sensor wire (the red dots in the photo) fitted properly again.

This excerpt from the Beogram 8002 schematic shows the wire function.

For a reference, here is speed sensor 0PE2

Hooking the Beogram 8002 components back up and checking the Play test again results in the speed control and braking functions doing their job.

The Beogram 8002 speed indicator now displays the full speed values (down to two digits) that it measures during operation of the platter.

Starting with Standby mode followed by 33.33 RPM and 45.00 RPM here are some photos.

Now I think all of the electrical functions of this Beogram 8002 are working correctly.
I will do some measurements tomorrow to verify that thinking but for now I am going to stop and enjoy the feeling of solving the problem :-).

Beogram From North Carolina: Reassembly and some early functional tests

Now that the capacitors have been replaced with new ones in this Beogram 8002 I can start reassembling components and try some functional tests.

One problem that I noted at the start of the project was that the output PCB (with the phono muting relay) has a broken wire. A lot of the wiring on this board looks kind of sloppy.

The other side of the little PCB has the relay. 

I removed all of the wiring, cleaned the pads and changed out the muting relay.

That's better.

Next is the removal of the tangential arm assembly for cleaning and lubrication.

The Beogram 8002 tangential arm assembly is similar to the Beogram 400x series design where two rails guide the arm assembly which is driven by a long threaded spindle.

Removal of the arm assembly from the two rails and the spindle begins by disconnecting the pulley that drives the spindle.

To do that the position sensor assembly (0PE1) is removed.

Once the pulley is removed the two rails and the spindle can be removed.

Here are the two rails and the spindle.  

Note that the spindle has a small threaded bushing on it with slots that fit onto a holder.

The black plastic holder fits over the rear rail (shaft).
Also note that the rear rail has rubber bushings on each end.  Those are for Beogram 8002 units that use a 60 Hz line voltage. 

After some cleaning of the parts I applied some new lubricants and reassembled the components.

For the two ends of the spindle that mount onto the Beogram 8002 frame I used a little bit of grease. In this case I used some Tri-Flow Red Grease.

For lubricating the spindle itself I used the same mixture of oil and grease that I use on Beogram 400x turntables. That is a mixture of dark gray Rocol MTS 2000 grease with Esso Nuto H44/H32 oil.  A good synthetic oil can also be used.  Just don't apply too much oil.

On the two rails the tangential arm rides on I applied some Molykote DX (white) paste like I apply to the rails on a Beogram 400x turntable.

I finished assembly of the tangential arm assembly by attaching the tonearm counterweight and the drive pulley. 

The tonearm counterweight on this Beogram was missing its set screw when it arrived so the counterweight was loose. I had a spare set screw to reattach it.

Now I focused back on the Beogram 8002 circuit boards.
On the microcomputer board I reinstalled the microcomputer IC with a new socket.  NOTE: Making sure to be properly protected against static electricity while handling the IC.

On the main board I installed a fuse for the +5 VDC power supply and I reflowed all of solder joints for board connectors.

The Beogram 8002 components are ready to be connected and a quick functional test.
I always leave off the platter drive connector to begin with.  That way I am using less power on the initial power on test and can check that the microcomputer board is working.

Plugging the Beogram 8002 power cord in results in the Standby indicator dot illuminating on the display.  So far so good.  I disconnected power, plugged in the platter drive connector and continued testing.

Pressing play results in the Beogram 8002 tonearm searching for a record and finding a set down point.
I will dive into more detailed power supply measurements next time but this initial check tells me that the Beogram is fairly close to working.

The record sensor is working properly as well as all of the tangential arm assembly controls.

I am seeing a problem though ... with the platter speed and braking.  In fact it appears that there is no braking and no speed regulation going on at the moment.

That could be an issue with the speed sensor for the platter but I will know more when I connect up some test equipment.