After addressing the fundamental components, such as the tracking system and platter motor, in the Beogram 4002 (5523) restoration project, I turned my attention to enhancing the electronic control system. This involved replacing electrolytic capacitors, baseline RPM trimmers, and the RPM and output relays. Additionally, I incorporated a grounding switch to connect system and signal grounds, a measure often effective in mitigating ground loop/humming problems.

Here are some noteworthy observations:

This image displays the main PCB prior to the rebuilding process:

A closer view of the RPM relay and trimmer section before restoration:

This image harks back to an era when relays were still manufactured in Germany. However, even a Siemens relay, despite its quality, can succumb to contact corrosion after 40 years. Replacing it with a modern, encapsulated Japanese relay of high quality is a prudent move. Another crucial upgrade for these turntables is substituting the single-turn RPM trimmers with 25x multi-turn units. This modification is essential for achieving accurate RPM calibration. Here, the new relay and the two 33 and 45 trimmers are visible:

These components are strategically positioned so that their trimmer screws are accessible from the opposite side of the PCB, enabling adjustments even when the PCB is installed.

This image showcases the main PCB after the rebuilding process, alongside the replaced parts:

While the visual appeal of the colorful Ta capacitors is undeniable, replacing them with modern, unassuming black aluminum cans is a wise decision. Exchanging the Ta units with modern Japanese 105C grade components is crucial, as the former can potentially overheat and fail catastrophically due to age-related short circuits between their electrodes.

With the main PCB addressed, I shifted my focus to the output board housing the output relay, as depicted in this image of the original board. It features the same Siemens relay found on the main PCB:

This image shows the board after replacing the relay, installing a new delay capacitor, and implementing the ground switch upgrade:

The final stage in overhauling the electronic system involved deoxidizing the contact tabs within the keyboard switches:

These tabs were in their original condition, eliminating the need for removal and straightening. To remove oxidation, I drew 2000 grit sandpaper through the contact areas and subsequently applied DeoxIT D100 using a cardboard strip as an applicator.

With all components restored, it was time for reassembly. I verified the motor RPM and fine-tuned the baseline RPM settings using my recently developed BeoloverRPM device:

After calibrating the 33 and 45 RPM settings, I conducted an RPM stability test. The BeoloverRPM device is capable of logging RPM over extended periods, recording measurements at 10-second intervals. It is sensitive to any sudden deviations, registering them through analysis of the standard deviation of the measurements. The following graph illustrates the RPM performance of this unit over approximately 8 hours:

The results are quite impressive. Minor variations within the 0.05% range are observable, aligning with the ‘wow and flutter’ specifications outlined in the service manual. A gradual, superimposed RPM drift of a similar magnitude is also present, possibly attributed to temperature fluctuations.

Currently lacking a reliable method to quantify the measurement error of the BeoloverRPM device, apart from comparing it to my Beogram 8000 with uProcessor-controlled RPM, I speculate that the actual variations are likely smaller than depicted. This assumption stems from the fact that measurement errors, being independent, would compound the actual variations.

In conclusion, following the test, I connected the turntable to my Beomaster 6000 4-Channel system and treated myself to my latest vinyl acquisition, “Aqualung” by Jethro Tull (Steven Wilson Remix). The audio quality was exceptional, a testament to the meticulous restoration process. This is Beolove in action!