In the previous post, I finished cleaning and deoxidizing the keypad and RPM panel. The keypad is now responsive, but the cueing up and down button is overly sensitive and needs further attention.

The RPM panel re-installation was put on hold because the plastic mounting fixtures were cracked, a common issue with Beogram 4002 turntables. I was fortunate that the cracks weren’t severe and the fixtures were still usable. To repair them, I used acrylic repair fluid while pressing the pieces together. Since this fix alone isn’t durable enough for frequent removal and re-installation, I reinforced it with Dura-Lar strips and epoxy on both sides of each mounting block.

The repaired mounting blocks attach to the aluminum frame with set screws located underneath. It’s important to note that the mounting screw for both the keypad and the RPM indicator panel sits directly below the RPM panel. This means the panel must be removed to access the keypad buttons or phono output board, highlighting the necessity of reinforcing the mounting blocks.

Next, I focused on verifying the voltages and signals from the Beogram’s detectors. The first check was the 4D1 LED and 4IC1 optical sensor, which detect the tangential arm’s position. The sensor reacts to light changes as the arm moves along the acrylic slide.

Following the service manual, I measured the voltage at the collector of the 4IC1 sensor with a transparent section of the slide between the LED and sensor. The voltage should be around 5V, and if not, adjusted using the 1R88 trimmer on the main board.

This adjustment is crucial because the run-out groove detection at the end of a record relies on a correctly set voltage level.

Next, I examined the fixed arm sensor, responsible for detecting the presence of a record and determining if it’s safe to lower the tonearm. The fixed arm has a light source directed at the platter, and an optical sensor reads the reflected light. A consistent, dim light signal, indicating a record is present, allows the stylus to be lowered. Without a record, the platter’s black ribs interrupt the reflected light, creating pulses that prevent the stylus from lowering.

This sensor’s signal needs to function correctly and at the appropriate level.

The sensor is producing pulses exceeding the required 6 volts, ensuring the tonearm won’t lower onto an empty platter.

Before checking the end groove and run-out stop circuit, I wanted to complete some mechanical checks and adjustments to prepare the Beogram for playback. I was pleased to find the platter-to-tonearm height was already at the required 23mm.

The arm lowering limit needed setting to ensure the stylus tip is approximately 1mm from the top of the first platter rib. This safety measure safeguards the cartridge from damage if the record detection circuit fails.

Another mechanical adjustment involved checking the tonearm’s length and parallelism. By running a string tangent to the Beogram arm assembly, I could visually confirm the stylus followed the string’s path.

I had previously confirmed the 7.7mm distance and parallelism between the tonearm and fixed arm when disassembling and cleaning the tonearm assembly earlier in the restoration.

With those steps completed, record playback is getting closer. The remaining tasks include fine-tuning the tracking sensor sensitivity, verifying the run-off stop function, and calibrating the platter speeds.

Adjusting the tracking sensor was relatively smooth, though it involved several iterations to achieve the desired sensitivity where the tangential arm motor moves after the correct number of revolutions.

The run-off stop check on the oscilloscope showed good results. I successfully adjusted trimmers 1R14 and 1R15 on the main board to set the 33⅓ RPM and 45 RPM speeds using the Beolover RPM tool.

These Beograms require a lot of adjustments and checks, but their exceptional design makes them well worth the effort.

Now, it’s time for a break with food and fireworks – away from the Beogram, of course. Afterward, I’ll make a quick adjustment to the keypad cueing button, and then it’s time to relax and enjoy some vinyl.