By popular request (really, I got quite a few emails about this!...;-), I finally completed my Beogram DC motor restoration video! It demon...
Wednesday, November 29, 2017
Beogram 4000: Restoration of the PCBs
After restoring the control cluster of the Beogram 4000 that is currently on my bench I did the PCBs. This shows the main PCB in its original condition:
I usually replace all electrolytic capacitors with new 105C grade Japanese units, put in a new RPM relay and I install new 25 turn encapsulated trimmers for the RPM adjustment. This enables a much more precise RPM adjustment compared to what is possible with the original single turn trimmers. The capacitors need to be replaced since often they dry out/start leaking and that is a recipe for operational trouble. This shows the RPM section in detail in original condition:
and with new components:
This shows the RPM trimmers from the solder side. Their adjustment screws poke through the holes that were used to adjust the original trimmers. This way one can adjust the RPM when the turntable is running:
This shows the entire PCB rebuilt together with the replaced parts:
There is one more PCB, the power supply:
It has only two electrolytic capacitors (the two red dots). To get to their solder points the PCB ends to be lifted up and that usually requires to unsolder the leads that go to the primary winding. They include an in-line mounted fuse that is protected by a yellow plastic tube. It is visible in the back of the PCB in the above picture. When I unsoldered the leads from their PCB terminals, one of the fuse mounts came loose:
Upon further inspection it became clear that the metal ends of the fuse had separated from the glass tubes:
So after replacing the two capacitors, I installed a new fuse into the mounting 'cups' that I bent a bit to ensure tight fit:
Then I soldered the fuse back into the primary line and enclosed it with a length of shrink tubing
And this is how it looks now after bolting the board back in:
On to rebuilding the reservoir and motor capacitors, and the AC platter motor itself....