Some time ago, I refurbished a Beogram 4002 DC platter motor for a client in California. However, even after the motor was reinstalled, the turntable still exhibited noticeable speed variations at 45 RPM. This often indicates a problem with the RPM relay, specifically oxidation. These relays tend to fail at 45 RPM first because most Beograms are typically used at 33 RPM, leaving the 45 RPM contacts unused and prone to oxide buildup. My client opted for a complete restoration of the ‘RPM chain,’ and I recently received the necessary PCBs and RPM adjustment panel.

I began with the main PCB:

My first steps involved replacing all electrolytic capacitors, followed by the installation of a new RPM relay and new RPM trimmers. Here are the original components:

And the updated components:

Afterward, I installed the board and, using an empty, rotating platter, I checked the record detection sensor signal at the collector of transistor TR4:

The signal appeared weak, suggesting that transistor TR4 had experienced a decrease in its gain (Hfe). Here’s a picture of the original TR4, a BC138C transistor, with its 1MOhm biasing resistor behind it:

To address this, I replaced it with a new 2N5089 high-gain transistor (Hfe of approximately 750). Properly biasing this transistor required substituting the 1MOhm resistor with a multi-turn 5MOhm trimmer. I temporarily installed the trimmer on the solder side to fine-tune the collector voltage to the specified 4V:

Next, I positioned it beneath the board, in the original resistor’s location:

After this modification, the sensor signal, measured with the platter empty, showed significant improvement:

The valleys in the signal, aligning with the black ribs on the platter, now approached 0V as outlined in the service manual.

With this, the main PCB restoration was complete:

Next, I focused on the output PCB, which also frequently suffers from relay oxidation. Here’s the original board:

I replaced the relay and the capacitor responsible for delaying relay activation after the needle drops onto the record. As a preventative measure, I added a switch to simplify grounding the system and signal in case of hum issues:

Finally, I replaced the incandescent bulbs that light the RPM panel scales with LED fixtures. This addresses another potential source of RPM fluctuation—heat from the original bulbs. Here are the original bulbs:

And the new LED boards:

With the light shields back in place:

I installed all the components into one of my Beogram 4002 turntables for testing. The 33 RPM LED illuminated:

The red-green LEDs used in these panels provide a realistic, incandescent-like glow and effectively illuminate the red indicator. Beautiful!

Finally, I tested the RPM performance using my BeoloverRPM device:

The BeoloverRPM can record RPM over extended periods. This graph illustrates the results of a 24-hour measurement at 45 RPM:

This level of stability is optimal for DC motors, indicating that this Beogram is ready to operate flawlessly again.