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Beolover SyncDrive: DC Platter Motor Replacement for Beogram 4002 and 4004 (Type 551x and 552x)

Late Beogram 4002 and the 4004 (Types 551x and 552x), which have DC platter motors instead of the earlier synchronous AC motors usually suff...

Monday, March 7, 2016

Beogram 4000: Replacing all Electrolytic Capacitors and the RPM Relay

After I rebuilt the arm lowering and tracking mechanisms of the Beogram 4000 that I am currently rebuilding it turned out that the 30V power supply for the solenoid had lost its reservoir capacitance causing a humming and vibrating solenoid, which prevented the arm lowering mechanism from working. So today's task was to rebuild the reservoir and motor capacitors and also replace all electrolytic capacitors on the PCBs with quality Japanese 105C grade units. I started out with the big cans. Here is a picture of the original setup:
Check my Beogram 4000 page for more information about the detailed set-up of the reservoir and motor capacitors and which leads connect where.

Before unsoldering the leads and removing the capacitors I prepared my capacitor assembly for installation:
The 3D printed red part organizes the capacitors and fits snugly into the original capacitors bay. This shows the set-up after installation:
The original mounting strap holds it in place. This assembly is available to other enthusiasts. Just send me an email.
Due to the humming solenoid issue, I measured the main reservoir capacitors. And indeed the two 3000uF cans were completely dead:
All capacitance gone. It is actually rare to find capacitors that are that dead in Beograms. More frequently they just have reduced capacitance. But after seeing this measurement, it was clear what happened to the solenoid: Its power oscillated at 120Hz due to the lack of stabilization.

After this I unbolted the main PCB and flipped it over to have a look:
Then I prepared a replacement RPM relay based on a modern encapsulated Japanese relay:
I recently had the breakout boards professionally manufactured, so this part now looks very professional.
Here it is after installation:
Then I replaced all electrolytic capacitors on the board:
Not to forget the lone capacitor soldered to the solder side of the board. Before:
and after:
The remaining two capacitors (red dots) were on the power supply board:
I replaced those too:
Then it was time to see if the solenoid now behaved better. And it did. On to the keypad and the carriage switches.

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