Bay Area Beogram 8002: Checking the Forward/Reverse Scanning LDR Devices

I left off the previous post thinking there was a possible problem with one of the Beogram 8002 forward/reverse scanning LDR devices.

In testing the resistance of the two LDR devices with +15 VDC on the light source I saw one LDR measure a lot different from the other.  I figured one of the devices had become faulty.

When I removed the two LDR devices and checked their resistance values again they measured a lot closer to each other.  

Note: Without a calibrated light source my comparison check was to place an LED work light about ten inches directly above an LDR and measure the resistance.  Then, without moving the light and checking the other LDR in the same place I could make the second device measurement. The measured resistance should hopefully be very close on both devices.

The measurements are not identical but they aren't as far off as I suspected.

I decided to go ahead and replace the two devices along with the light source.
Since this Beogram involves some shipping costs I feel that it is safest to go with new components here.

Here are the new scanning components installed.

A new lamp source (LED with 1KΩ resistor) and two LDR devices.

I repeated the adjustment procedure on the two LDR devices again.  This time the two screws that control the light flow to the LDR devices both have working room for future adjustments. Both LDR devices were able to adjust to the desired, neutral voltage level.

Unfortunately there was still a problem. The activation mechanics of the forward scan button did not feel right to me. It didn't return to its original position quickly.

I took the button panel apart again to investigate the mechanics of the spring. 
I also compared a few other button panels from Beogram 8000 and 8002 units.

This photo shows the button side of the panel and where the scanning buttons strike the spring mechanism.  Both buttons share a single spring mechanism is kind of like a teeter-totter (or seesaw).  Pressing a scanning button causes that side of the teeter-totter spring to go down.  The other side will try to go up but is blocked by the back of the button panel. So each button should perform on its own side of the spring mechanism. 

Pressing a button depresses the spring. Releasing the button results in the spring returning to its neutral position.

What I observed in manually operating the spring mechanism is that the portion of the spring with the aperture would not return all the way to neutral when it was released. 

That is why the screw that controls the light source to the LDR had to be opened up so much for the reverse scanning LDR.

The neutral position should have full exposure of the LDR to the light source and the light source control screw positioned so the neutral position LDR voltage measures between 620mV and 700mV.

When a scanning button is partially pressed down, the opening (aperture) in the spring moves in front of the LDR cutting off some of the light.  That results in the resistance value increasing which in turn, causes the voltage level for that LDR to increase.  When the button is fully depressed the LDR is completely cut off from the light source and the maximum voltage across the LDR occurs...which is the fast scan operation.

The following photo shows that the spring mechanism with the apertures for the LDR devices just sits in place, resting on the center pivot point. It can teeter-totter either direction.  That surface of the spring mates to the underside of the button panel.

I have the spring lifted up and away from the panel in this photo to show the pivot point more clearly.
When fully installed the pivot point rests on the plastic base below it.

I removed the spring mechanism completely to adjust it.

After a few iterations of bending the spring (at the pivot point and at the ends) I achieved a much better result of the scanning button action on the spring mechanism.

Both the forward and reverse LDR devices were able to adjust to a good neutral value and more importantly, they return to that neutral position after being engaged.

All of the Beogram 8002 operating functions still work and I am happier with the scanning buttons now.
I will keep an eye on them when I get to the listening tests