Beogram 8000: Final Steps

I was kind of lucky I suppose in finding the intermittent pause culprit on the first suspect. However it was the most likely when reviewing the problem. Even though the behavior was intermittent it lined up with a problem Beolover had on a Beogram 8002 project earlier. After replacing the Beogram 8000 original control panel board with one of my spares -

the result has been over twenty error-free record plays.

Returning to the original control panel board to look at repair options I examined the LDR (photoresistor) devices for the forward and reverse controls.

Visually examining them and testing their resistance with different light sources didn't reveal any problems. These devices can become unreliable over time and exhibit the intermittent behavior I experienced so I decided to apply the repair Beolover did on the Beogram 8002.

I ordered the same LED from Newark and some GL5549 LDR devices from a couple of different sources. Replacing the original lamp with an LED requires a load resistor so I used the 1K ohm value Beolover had set his to.

Using the same parts I was hoping the fix would just be a quick install, test and go operation. Unfortunately I found that these GL5549 LDR devices vary in performance by quite a bit. It took quite a while to find a pair of these new LDRs to match and be around 20K ohms when in place on the board.

After finally finding a couple of acceptable LDR devices to try I mounted them with some temporary glue to secure them in their respective mounting slots.

I prepared the control panel board for re-installing into the Beogram. That included adding my little LDR test connector. This time I used 30 gage hook-up wire so the test connector can be left in the control panel. I matched the wire colors to what the Beogram 8000 colors are for the LDR measurements. That makes it easier to remember later if I have to retest the LDR voltages.

The connector is also a female connector so I don't have to worry about anything shorting by it when I leave it in the Beogram.

Testing the reworked control panel board with the new LDRs was interesting. I ended up having to re-adjust the position of one of the LDR devices. That is why I use glue that isn't permanent. Eventually I was able to get the forward and reverse LDRs adjusted within the 600mV - 700mV range necessary for successful operation. The service manual originally asked for 620mV but later updated that value to 650mV. I talked to another Bang & Olufsen technician who told me a solid value between 600mV and 700mV is sufficient.

As you can see in the picture above, the adjustment for a working forward and reverse operation resulted, again, in quite an imbalance in the adjustment screws of the control panel board. The voltages are stable though so I am going to run another play test with this board just to see what happens.

For this project though I am inclined to go with the replacement control panel board that I ran the twenty successful record plays with. The forward and reverse LDR controls are closely matched on that board and I feel will be more of a sure thing. This replacement repair is looking good but I will feel better about it if I can do a long term test with it.

There is one more issue that cropped up during the play testing of this Beogram 8000. Another intermittent problem but one that was easily recognized. A couple of times after a record completed play I noticed that the phono mute did not occur. That means the Beogram phono mute relay is acting up. This picture shows where the muting relay is located. It is easy to get to but does require opening up the Beogram case again. Oh well.

I hadn't planned on replacing this relay but since it has come up I asked the owner if he would like the phono grounding switch to be added. This is a convenience option that Beolover has been doing on Beogram 400x and 800x turntables. The added switch gives a user the option of setting the turntable up as it is originally or shorting the phono signal ground to the Beogram chassis ground.

This is a nice feature for Beogram owners that use the turntable with a non-B&O amplifier. I pair a lot of my Beogram units with my Yamaha C2a, C2x and C-70 preamplifiers. Those pre-amps support two turntable inputs but require using RCA jacks. When I add the DIN to RCA converter I get a hum in the phono signal unless I attach an extra grounding wire on the adapter to the amplifier chassis ground lug. With this switch added to the Beogram I can short the phono signal grounds to the chassis ground in the Beogram and not need the extra grounding wire on the cable adapter.

It's doesn't seem like a big deal but it is nice to have options so we are adding the switch to this Beogram.

First I need to removed the faulty muting relay.

This muting relay is different than the one in the Beogram 8002 turntable where Beolover was able to replace it with a new Omron sealed relay device. That relay pin layout is not a match for this Beogram 8000 output signal board. My only option here is to take a newer output relay from one of my later model Beogram 8000 spares.

If I didn't have a spare I would have removed the clear plastic cover and tried to clean the relay contacts. That still might not have solved the problem if it is in the relay coil.

I installed the new muting relay and then attached the grounding switch.

I used some hot glue in the gap between the output board case and the switch case. This helps secure the switch.

Now it is back to the record play testing again. Success of these tests will result in this Beogram being packed up to return home.