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Tuesday, May 23, 2017

Beogram 4004 (5526): Restoration of PCBs and Reservoir Capacitor

After restoring the arm lowering and tracking systems of the Beogram 4004 (5526) that I am restoring right now it was time to rebuild the PCBs and install a new reservoir capacitor. This shows the original main PCB of the deck:
And after replacing all electrolytic capacitors as well as the RPM trimmers and the RPM relay:
This shows the rebuilt RPM section in detail:
I usually replace the original single turn trimmers with modern encapsulated 25 turn units, which greatly enhances the accuracy with which the RPM can be adjusted. The replacement relay is a Beolover design that uses a modern encapsulated SMD relay to replace the original National relay. This shows the original and new relay in comparison:
On to the output PCB with the output relay circuit and (in the case of the 4004) additional circuitry to enable remote control via the Beomaster 2400. This shows the board in original condition:
A detail shot of the relay section:
I usually install a new relay and a switch that allows connecting signal and system grounds together, which usually is a reliable method to quench any hum that may occur when connecting to non-B&O amplifiers that use RCA jacks:
This shows the entire board in restored condition:
The remaining part of the PCB restoration is to replace the original reservoir capacitor with a new one. This shows the original capacitor:
And this shows the replacement, which uses a 3D printed adapter to fit a modern (smaller) capacitor under the original clamp and into the compartment in the metal chassis:
The next step will be to install LED lights into the RPM trimmer scales.

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