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Sunday, June 5, 2016

Beogram 4002 (5513): Rebuilding the PCBs and Restoring the 33 RPM Function

Usually, I first restore the arm lowering and tracking systems in Beogram 4002 turntables. However, in this Beogram 4002 (5513) I first needed to get the control system working and so I elected to do the PCBs first. When I unpacked it a quick check revealed that the platter motor would come on whenever the deck was plugged in. Well, a second look revealed that the seller had plugged the motor into the stand-by LED header that is present on all 5513 circuit boards but rarely used. This puts a few volts towards the motor and it starts spinning when line power is established. Very funny!
After recognizing this I plugged the motor into the correct socket, and now it would not do anything when I started the deck up. However, I was able to switch it to 45 RPM (after start) and the motor would spin. This suggested that the RPM relay had an issue, probably corrosion, preventing it from making contact for the 33 RPM setting.
I decided to simply do my standard 'exchange all electrolytic capacitors and RPM relay and trimmers' procedure and hope for the best. Here are a few pictures of my progress. This shows the main PCB in its original condition:

All the red and blue parts need to be replaced. this shows the 'RPM section' in detail:
I replaced all electrolytic capacitors with new Japanese made 105C grade units and put in one of my plug-in ready relay replacements that are based on encapsulated SMD relays soldered to a custom designed breakout board:

Here is a detail shot of the RPM section:

The trimmers are 25 turn encapsulated units. Only high resolution trimmers like this allow a precise adjustment of the RPM. The original standard single turn trimmers can be very tricky to adjust to get a precise 33.3 RPM setting. My relay assemblies are available to other enthusiasts. Just send me an email, or use the contact form on my blog if you need some.

While I was at it, I also rebuilt the output PCB (#8) with a new grounding relay and a new delay capacitor for the relay activation. This shows the board in its original condition:
And after replacing the parts:
As usual, I also installed a grounding switch (red) that allows to connect signal and system grounds in case there is a hum at the output.

After putting the boards back in, the 33 RPM issue was fixed, i.e. it was indeed the relay that caused the malfunction. On to the arm lowering and tracking mechanisms!


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