By popular request (really, I got quite a few emails about this!...;-), I finally completed my Beogram DC motor restoration video! It demon...
Thursday, May 5, 2016
Beogram 4002 (5524): Rebuilding the Main and Output PCBs
I recently received the main and output (#8) PCBs of a Beogram 4002 (5524) as well as the DC motor for restoration from a customer in the UK. The parts came with the indication that the platter RPM is fluctuating and that the arm would not lower at the 30 cm set-down point when the deck is started.
I started out by giving the PCBs my standard treatment, i.e. I replaced the electrolytic capacitors and put in a new encapsulated modern relay and I replaced the single turn trimmers that are used to tune the RPM with modern 25 turn units. Only with such potentiometers it is possible to adjust the RPM precisely (check out my BeoloverRPM device that makes this very simple).
Here are a few impressions of my 'process': This shows the main PCB before restoration. The red and blue components are the capacitors that need to be replaced.
This shows the 'RPM section' in original condition:
And after replacing the parts:
This shows the RPM trimmers from the solder side of the PCB:
I install them in a way that RPM increase corresponds to a CW turn, which is more practical than the original CCW setting of the single turn trimmers.
The replacement relay assembly is available to other B&O enthusiasts. Just send me an email or use the contact form. In my experience it is essential to replace the relay and the trimmers if a solid RPM performance is desired.
This shows PCB#8 that controls the output relay before rebuild:
This shows the rebuilt PCB:
As usual, I added a switch that allows tying signal and system grounds together, which can be useful to combat hum if a DIN5 to RCA adapter without ground breakout is used.
On to rebuilding the motor with freshly oil infused brass bearings.