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.
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